Divergent Synthesis of Cyclopropane-Containing Fragments and Lead-Like Compounds for Drug Discovery

Home , Cyclopropane, Dicarbonate

A Thesis submitted by

Stephen John Chawner

In partial fulfilment of the requirement for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

Imperial College London

South Kensington London

SW7 2AZ

United Kingdom 2017

I confirm that the work presented within this document is my own. Clear acknowledgement has been made when referring to the work of others, or where help has been received.

The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the licence terms of this work.

Acknowledgements

Firstly, I would like to thank Imperial College London and Eli Lilly whose combined generosity through a CASE award made my PhD financially possible.

I would like to thank my academic supervisor Dr James Bull for providing me with the opportunity to undertake a PhD in his group. I am grateful for the chemistry knowledge that he has shared, his encouragement to present at conferences and the freedom to follow new project ideas.

In addition to funding, the CASE award provided me with the opportunity to collaborate with Dr Manuel Cases-Thomas at Erl Wood. Manuel was a constant source of enthusiasm throughout my PhD and has been a joy to work with.

I would like to thank all the Bull, Armstrong and Bures groups, past and present, with whom I have had the pleasure to work alongside in the Heilbron lab. In particular, I would like to thank Dr Tom Boultwood for his early and valuable training on glovebox usage, Dr Owen Davis for the countless discussions on the applications and benefits of cyclopropanes and oxetanes within medicinal chemistry, and Dr Dominic Affron for sharing his extensive theoretical and practical chemistry knowledge, as well as his experiences with Swern reactions. In addition, I would like to thank Owen, Dom, Ethan, Rosie and Sahra for reading through sections of this thesis and providing valuable feedback.

Thank you to all the scientists with whom I worked with whilst on my industrial placement at Erl Wood; you made my time there a fantastic experience. In addition, I would particularly like to thank the Eli Lilly HPLC and crystallography teams whose efforts are very much appreciated.

I am grateful to the NMR staff at Imperial College London as well as the mass spectrometry staff at both Imperial College London and the EPSRC mass spectrometry centre.

I would like to thank Lisa for being supportive over the last few years and putting up with all the chemistry talk.

I want to thank my late grandparents James and Joan, for helping me along the scientific path from an early age. Finally, I wish to express my utmost gratitude to my parents, John and Ann, for all their love and encouragement throughout the years. Their support helped give me the strength to overcome the challenges that stood between where I was and where I wanted to be.

Abstract

The cyclopropane ring is key to a large number of medicinally-relevant compounds that possess a broad spectrum of biological activities. This thesis details the preparation of novel bifunctional cyclopropanes through a divergent functionalisation approach utilising two readily accessible cyclopropyl-scaffolds (Figure 1). The cyclopropanes generated sampled new areas of chemical space whilst being suitable 3-dimensional fragments and lead-like compounds for drug discovery.

A) B) CO2Et CO2Et EtO2C Cyclopropanation SPh A N 2 SPh SPh Bifunctional B cyclopropyl scaffolds

Figure 1: A) General concept for a bifunctional cyclopropyl-scaffold able to undergo divergent functionalisation on functional handles A and B. B) Synthesis of bifunctional cyclopropyl-scaffolds

A novel CoII-catalysed cyclopropanation generates two diastereoisomeric bifunctional cyclopropyl-scaffolds from commercially available reagents in an excellent yield and can be conducted on multi-gram scales. Asymmetric cyclopropanation has been explored with max ee = 73%. Divergent functionalisation of the ester was explored, utilising hydrolysis, reduction and amidation reactions to create a variety of functionalised cyclopropyl sulfides. The sulfide synthetic handle was oxidised to give the corresponding sulfoxides or sulfone selectively. Sulfoxide–magnesium exchange was explored and the cyclopropyl-organometallic species generated was trapped with a variety of electrophiles to create a diverse range of cyclopropane-containing products. The cyclopropyl-organometallic species was also utilised in Negishi cross-coupling, proving to be a versatile method to attach an aromatic or heteroaromatic directly onto the cyclopropane ring.

CO2Et Electrophile CO2Et CO2Et RMgX E Ph S MgX CO Et O (Het)aryl-X 2

(Het)aryl

Scheme 1: Divergent functionalisation of the trans-substituted cyclopropyl-scaffold via sulfoxide–magnesium exchange followed by either electrophilic trapping or cross-coupling. The same methodology has been used to functionalise the cis-substituted cyclopropyl scaffold too.

Table of Contents a) Glossary of Abbreviations, Acronyms and Symbols ...... 9 b) Stereochemical Notation ...... 13

1. Introduction ...... 14 1.1. Overview of the Drug Discovery Process ...... 14 1.2. Attrition in Drug Discovery ...... 15 1.3. Introduction to Chemical Space as a Tool for Medicinal Chemists ...... 18 1.4. Molecular properties for Drug-Like Compounds ...... 19

1.4.1. Molecular weight (MW) ...... 20 1.4.2. Lipophilicity ...... 21 1.4.3. Polar Surface Area (PSA) ...... 22 1.4.4. Fsp3 ...... 22 1.4.5. Aromatic Ring Count ...... 23 1.4.6. Undesirable Functional Groups ...... 23 1.5. Physicochemical Guidelines for Drug-Like Compounds ...... 23 1.6. Compound Library Construction Approaches ...... 25 1.6.1. Combinatorial Chemistry ...... 25 1.6.2. Lead-Oriented Synthesis (LOS) ...... 27 1.6.3. Fragment-Based Drug Discovery (FBDD) ...... 29 1.7. Cyclopropanes within Drug Discovery ...... 34 1.8. Common Methods to Synthesise Functionalised Cyclopropanes ...... 37 1.8.1. Michael-Initiated Ring Closure (MIRC) ...... 37 1.8.2. Simmons-Smith Cyclopropanation ...... 41 1.8.3. Diazo Compound-Derived Carbene Insertion into an Alkene ...... 44 1.8.4. Cross-Coupling of a Pre-Functionalised Cyclopropyl-Species ..... 53 1.9. Project Aims ...... 55 2. Results and Discussion ...... 58 2.1. Transition Metal-Catalysed Cyclopropanation of Phenyl Vinyl Sulfide with Ethyl Diazoacetate ...... 58 2.1.1. Bomb Calorimetry of PVS, EDA and Product Cyclopropanes ...... 59 2.1.2. CuI-Catalysed Cyclopropanation of PVS with EDA ...... 61

2.1.3. CoII-Catalysed Cyclopropanation of PVS with EDA ...... 77 2.1.3.1. CoII-Catalysed Cyclopropanation Optimisation ...... 76 2.1.3.2. Purification of Large-Scale Cyclopropanation Reactions ..... 82 2.1.3.3. Open-Flask CoII-Catalysed Cyclopropanation ...... 93 2.1.3.4. Cyclopropanation of Alternative Reagents ...... 97 2.1.3.5. Conclusions ...... 101 2.1.4. Asymmetric Transition Metal-Catalysed Cyclopropanation ...... 102 2.1.4.1. Asymmetric CuI-Catalysed Cyclopropanation of PVS with EDA ...... 106 2.1.4.2. Asymmetric CoII-Catalysed Cyclopropanation of PVS with EDA ...... 110 2.1.4.3. Isolation and Characterisation of Single Enantiomers ...... 121 2.1.4.4. Conclusions ...... 123 2.2. Scaffold Functionalisation: Ester Derivatisation ...... 125 2.2.1. Hydrolysis ...... 125 2.2.2. Amidation ...... 127 2.2.3. Reduction to an Alcohol ...... 130 2.2.4. Transesterification ...... 132 2.2.5. Conclusions ...... 133 2.3. Scaffold Functionalisation: Sulfide Derivatisation ...... 134 2.3.1. Oxidation ...... 134 2.3.2. Sulfoxide–Magnesium Exchange, Electrophilic Trap Protocol ... 136 2.3.2.1. Reaction Optimisation ...... 146 2.3.2.2. Stability Investigations into Cyclopropyl-MgCl Intermediate ...... 151 2.3.2.3. Electrophile Scope for trans-Cyclopropyl Scaffold ...... 154 2.3.2.4. Electrophile Scope for cis-Cyclopropyl Scaffold ...... 157 2.3.3. Sulfoxide–magnesium exchange, Negishi cross-coupling protocol ...... 159 2.3.4. Conclusions ...... 162 2.4. Sequential Scaffold Functionalisation using Both Synthetic Vectors . 163

2.4.1. Sequential Scaffold Functionalisation: Amidation and Oxidation ...... 163 2.4.2. Sequential Scaffold Functionalisation: Sulfoxide–Magnesium Exchange, Negishi Cross-Coupling and Amidation ...... 164 2.4.3. Sequential Scaffold Functionalisation: Sulfoxide–Magnesium Exchange, Negishi Cross-Coupling and Reduction ...... 165 2.4.4. Conclusions ...... 166 2.5. Physicochemical Property Analysis ...... 167 2.5.1. Synthesised Cyclopropane-Containing Compounds ...... 168 2.5.2. Virtual Cyclopropane-Containing Compounds ...... 173 2.5.3. Conclusions ...... 177 3. Conclusions and Future Work ...... 178 3.1. Conclusions ...... 178 3.2. Future Work: Biological Screening ...... 181 3.3. Future Work: Asymmetric Cyclopropanation ...... 181 3.4. Future Work: Recovery of CoII Catalyst ...... 186 3.5. Future Work: Expansion of the Cyclopropyl Scaffold Derivatisation Methodology ...... 186 4. Experimental ...... 189 4.1. General Experimental Considerations ...... 189 4.2. Experimental Details and Characterisation Data ...... 191 4.3. Chiral HPLC Data for Enantiopure Cyclopropanes (1S,2R)-15, (1R,2S)-15, (1S,2S)-16 and (1R,2R)-16 ...... 259 5. References ...... 261 6. Appendices ...... 274 6.1. Appendix 1 – Divergent Synthesis of Cyclopropane-Containing Lead-Like Compounds, Fragments and Building Blocks through a Cobalt Catalyzed Cyclopropanation of Phenyl Vinyl Sulfide, S. J. Chawner, M. Cases-Thomas, J. A. Bull, 2017, 34, 5015-5024...... 274

a) Glossary of Abbreviations, Acronyms and Symbols

2-MeTHF 2-methyl tetrahydrofuran [�] specific rotation measured at 20 °C using irradiation with a wavelength equal to the sodium D-line (589 nm) D reflux µmol micromole(s) µM micromolar µW microwave irradiation ® Trademark registered with the USPTO ™ Trademark nmax infrared absorption maximum Å angstrom Ac acetyl group ADMET absorption, distribution, metabolism, excretion, toxicology AlogP atomic logP APCI atmospheric pressure chemical ionisation aq aqueous Ar aromatic ASAP atmospheric solids analysis probe Atm atmosphere(s) Boc t-butyloxycarbonyl BOX bisoxazoline Bn benzyl Bu butyl Bz benzoyl cat catalyst Cb N,N-diisopropylcarbamoyl clogP compound logP CI chemical ionisation COSY homonuclear correlation spectroscopy d doublet Da Dalton

dba dibenzylideneacetone DEPT-135 distortionless enhancement of polarisation transfer DIBAL diisobutylaluminium hydride DIPEA N,N-diisopropylethylamine DMF N,N-dimethylformamide DMSO dimethyl sulfoxide dr diastereomeric ratio E generic trapped electrophile

EC50 half maximal effective concentration ee enantiomeric excess EDA ethyl diazoacetate EI electron impact ionisation equiv equivalent(s) ES electrospray ionisation Et ethyl EWG electron-withdrawing group FBDD fragment-based drug discovery Fsp3 The fraction of carbons in a molecule possessing sp3-hybridisation FTMS Fourier transform mass spectrometry gem geminal h hour(s) HATU 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo [4,5-b]pyridinium 3-oxid hexafluorophosphate

HBA hydrogen bond acceptor

HBD hydrogen bond donor hERG human ether-a-go-go-related gene

HMPA hexamethylphosphoramide

HPLC high performance liquid chromatography

HRMS high resolution mass spectrometry

HTS high throughput screening

Hz Hertz

IR infrared i iso

IC50 half maximal inhibitory concentration

IP intellectual property

J coupling constant

Ki inhibitory constant

L ligand

LCMS liquid chromatography–mass spectrometry

LDA lithium diisopropylamide

LiTMP lithium 2,2,6,6-tetramethylpiperidine

LOS lead-oriented synthesis m multiplet m meta

M molar or generic transition metal

MALDI matrix-assisted laser desorption/ionisation

Me methyl min minute(s) mmol millimole(s) mM millimolar mp melting point

MS molecular sieves

MW molecular weight

NCS N-chloro succinimide nm nanometre nM nanomolar NMI N-methylimidazole

NMR nuclear magnetic resonance NSI nanospray ionisation o ortho p para Ph phenyl pKaH acidity constant of the corresponding conjugate acid PMI principal moment of inertia ppm part(s) per million Pr propyl PSA polar surface area PyBOX pyridine-bisoxazoline PVS phenyl vinyl sulfide py pyridine quat quaternary carbon R generic alkyl group R&D research and development

Rf retention factor

RL comparatively large R group RM generic organometallic species

RS comparatively small R group rt room temperature (approximately 22 °C) s singlet or second(s) SFC supercritical fluid chromatography SOMO singularly-occupied molecular orbital t triplet t1/2 half-life t-BDA tert-butyl diazoacetate TBME tert-butyl methyl ether t, tert tertiary THF tetrahydrofuran TLC thin layer chromatography ToF time-of-flight

b) Stereochemical Notation

Throughout this thesis, representations of stereochemistry are consistent with the convention proposed by Maehr,1 in which solid and broken bold lines are used to denote relative configuration, and solid and broken wedges represent absolute configuration (Figure 2). Where relative configuration is depicted the compound has been prepared as a racemate, whereas when absolute configuration is shown a compound is enantioenriched or has been prepared as a single enantiomer.

relative absolute configuration configuration Figure 2: Depiction of relative and absolute configuration used within this thesis

When representing absolute stereochemistry, broken wedges are used with the convention of the narrow end of the wedge originating from the stereogenic centre, with the wedge widening with increasing distance from the stereogenic centre (Figure 3).

CO Et 2 H H = EtO2C SO Ph SO2Ph 2 Figure 3: The use of wedges to illustrate absolute stereochemistry

1. Introduction 1.1. Overview of the Drug Discovery Process The drug discovery process is the route by which potential new medicines are discovered and developed. The process begins with identification of the biological target, followed by hit identification and optimisation, preclinical (in vitro) trials, clinical (in vivo) trials and finally drug launch. Producing a marketable drug from an initial hit often takes 10–15 years at a cost estimated around US$2.6 billion per successful compound.2 Figure 4 shows the 10 stages of drug discovery and development, from identification of the biological target through to a successful drug reaching the market.

Target Hit Lead Lead Preclinical identification identification identification optimisation trials

Phase I Phase II Phase III Submission Market

Figure 4: The 10 stages of drug discovery and development

Target identification – Identification and validation of the biological target and its drugability. Hit identification – Identification of compounds that bind to the biological target and which act as the starting points for optimisation. Lead generation – Focusses the ‘hits’ to one or a small number of lead compounds. Lead optimisation – Optimises the ‘lead’ compound(s) to generate a drug-like compound which displays desirable properties and physiological behaviours.

Preclinical trials – May vary depending on the compound, but generally compounds undergo pharmacodynamic, pharmacokinetic and ADMET testing. Typically, both in vitro and in vivo testing will also be undertaken. These tests allow dosage estimation and compound formulation optimisation, in addition to predicting drug-related toxicity. Phase I – A small-scale trial in human volunteers who are generally healthy. Results give information on dosage, pharmacokinetic parameters and toxicology in humans. Phase II – A small/medium-scale trial in human volunteers to determine drug efficacy and side-effects. Phase III – A large-scale trial aimed at confirming drug safety and efficacy in large patient populations. Submission – Submission to regulatory review prior to the drug reaching the market. Marketing – Matters including advertising and product packaging are addressed to maximise sales, with the aim of achieving profit to cover the costs of the total drug discovery and development process, and to keep the company viable.

1.2. Attrition in Drug Discovery The continued existence of the drug discovery industry in its current form is under very real threat.3,4 This is a result of key patent expirations, legal entanglements and declining patient confidence over concerns in transparency and integrity all resulting in ever-diminishing revenues, combined with increasing regulatory requirements and low research and development efficiency which are increasing drug development costs.3,4

The low R&D efficiency observed stems from the large number of compounds that enter drug development for only one to emerge as a drug. Attrition is the term used for this decline in the number of compounds during progression through the drug discovery process. Attrition is extremely costly to pharmaceutical companies as vast amounts of time and resources are expended on compounds that are not going to result in a marketable drug at the end of the process.5 Figure 5 shows the attrition rates for various drug discovery and development stages, according to data obtained from a recent review of pharmaceutical R&D productivity by Paul and co-workers.5

The stages with the highest levels of attrition are the preclinical trials and clinical trial phases I, II and III with 31%, 46%, 66% and 30% attrition rates respectively.

100 90 80 66 70 60 46 50 40 31 30 25 30 20 15 20 9

Phase attrition rate (%) rate attrition Phase 10 0

Figure 5: Attrition rates for the stages of drug discovery and development

The same review showed the cost per work in progress for each phase, which is illustrated in Figure 6. It is clear to see that phase III clinical trials are by far the most expensive per work in progress, followed by phase II clinical trials. From a financial perspective, the stages that are the most expensive per work in progress should possess the lowest attrition rates. To achieve this, the reasons for late-stage attrition need to be identified and rectified at an earlier stage in the drug discovery process.

160 150

140

120

100

($ million) ($ 40 40 40 15 20 10 1 2.5 5 0 Cost per work in progress per phase phase per progress in work per Cost

Figure 6: The cost per work in progress per phase for the stages of drug discovery and drug development

Combining the data from Figures 5 and 6 generates Figure 7, which shows the phase cost (uncapitalised) per launch for each phase of the drug discovery and development process.

250 235

200 185 146 150 128

100 62 49 44 50 24

0 Phase cost per launch ($ million) million) ($ launch per cost Phase

Figure 7: The phase costs (uncapitalised) per launch for the phases of drug discovery and development

Figure 7 shows that the four most expensive stages of drug discovery per launch are phase III clinical trials, phase II clinical trials, lead optimisation and phase I clinical trials. The major reasons for the three phases of clinical trials being so expensive are the high cost per work in progress and the high attrition rates, whereas the primary reason for lead optimisation being an expensive phase overall is the large number of compounds required to generate the optimised molecule. This shows that the drug discovery process would obtain enormous financial benefits from earlier optimisation practices which reduce attrition during late-stage clinical trials.

Kola and Landis identified the most prominent causes of attrition during 1991 and 2000, and that the impact of these factors has changed over that time period.4 In 1991 the largest causes of attrition were poor pharmacokinetic behaviour, insufficient bioavailability and insufficient efficacy. By 2000, poor pharmacokinetic behaviour and insufficient bioavailability accounted for less than 10%, with the major contributors now being toxicological and clinical safety issues and a lack of efficacy. More recently, an analysis of combined data on the attrition of drug candidates from AstraZeneca, Eli Lilly and Company, GlaxoSmithKline and Pfizer determined the major reasons for

attrition during both halves of the 2000–2010 decade.3 Between 2000–2005 the most significant causes were non-clinical toxicity (40%), clinical safety (13%), rationalisation of company portfolio (13%) and efficacy (11%). Rationalisation of company portfolio could occur if the disease area no longer appears commercially viable or a mechanism being shown to have efficacy or safety issues. Between 2006–2010 the primary causes were very similar, being non-clinical toxicity (40%), rationalisation of company portfolio (32%), and clinical safety (8%). This further indicates that the current lead causes of attrition in the drug discovery industry are non-clinical toxicology, clinical safety and efficacy. By separating the data into the corresponding drug discovery phases it was found that non-clinical toxicology was most prominent in preclinical trial attrition, clinical safety issues were most prominent in phase I attrition and a lack of efficacy was most prominent in phase II attrition. There were not enough data points in this publication to obtain statistically relevant information on attrition in phase III.

In an effort to reduce attrition within drug discovery the causes of non-clinical toxicity were investigated. To do this, correlations between toxicological success and compound physicochemical properties were studied. To illustrate and understand the effects of various physicochemical properties, the concept of chemical space can be employed.

1.3. Introduction to Chemical Space as a Tool for Medicinal Chemists Chemical space is a multi-dimensional concept that serves medicinal chemists as a kind of map to illustrate the distribution of molecules and their properties.6,7 Each different molecule possesses a variety of molecular properties (e.g. molecular weight, lipophilicity, number of hydrogen bond donors, number of hydrogen bond acceptors, Fsp3) which are termed molecular descriptors. To visualise a compound’s location in chemical space, it’s molecular descriptors are quantified, assigned a dimension and plotted on the resulting multi-dimensional graph, generating a data point unique to that molecule, called its property space. Due to the difficulty in expressing a graph with > 2 dimensions, chemical space representations are often simplified to 2 dimensional plots illustrating lipophilicity vs. molecular weight, with other molecular descriptors sometimes being displayed alongside. The multi-dimensional chemical space can

also be mapped into two-dimensional plot space through dimensionality reduction techniques such as principal component analysis (PCA)8 and self-organising maps (SOM)9.

Not all chemical space is useful to medicinal chemists.6 Out of the vast possibilities, only a small proportion of chemical space can provide medicinally-relevant molecules.6 By plotting the property space data points for known successful biologically active molecules, the regions of medicinally-relevant chemical space can be uncovered, and in doing so desirable molecular properties can be determined.6 Likewise, the property space data points for compounds that have failed to pass successfully through drug development can be plotted, aiming to correlate the value of a particular molecular property with the observed drug developmental failure.6 This could identify medicinally-undesirable regions of chemical space and therefore medicinally-undesirable molecular properties, which should be avoided to improve compound success rates within the pharmaceutical industry. Through such investigations, a wide number of physicochemical properties have been implicated in toxicology-induced attrition.

1.4. Molecular Properties for Drug-Like Compounds Small molecule drugs exert their biological action by binding to specific functionality of the target in such a manner as to modulate biochemical processes to elicit the desired physiological response. The magnitude and specificity of binding depends on the complementarity between the drug molecule and its target in terms of shape, chemical functionality and polarity. Shape complementarity maximises the interactions that can be achieved between the drug and the desired biological target. The incorporation of complementary chemical functionality offers directional and specific modes of binding, achievable through the formation of hydrogen bonds and p-p stacking interactions between the drug and the biological target. Binding potency can also be enhanced through non-directional interactions such as polarity-based hydrophobic attraction and Van der Waals interactions, though over-reliance on these can be detrimental to binding selectivity.

Whilst developing a drug to possess key interactions that produce both potency and selectivity, the overall properties of the molecule must not be overlooked. The physicochemical properties of a molecule can have a drastic effect on the probability of successful passage through drug development, with the following physicochemical properties being implicated in toxicology-induced attrition.

1.4.1. Molecular Weight (MW)

Excessive MW is widely regarded as one of the most significant causes of off-target toxicity within drug discovery. An excessive MW has also been associated with high plasma protein binding, which reduces the amount of compound available to elicit the 10 desired pharmacological response. Similarly, on average as MW increases, so does 10 the amount of compound binding to brain tissue. The effect of MW on hERG inhibition has also been investigated, through the analysis of 35200 molecules screened in a hERG inhibition assay.10 Inhibition of the hERG potassium ion channel has the possibility of QT prolongation which can result in fatal cardiac arrhythmia. It was found 10 that hERG inhibition steadily increased as MW increased.

In addition, on average as the MW of a compound increases, it’s biological solubility decreases.10,11,12,13,14 For an orally administered drug, a lower solubility reduces the amount of drug available to permeate the gastrointestinal membrane and enter systemic circulation. Excessive MW also has a detrimental effect on cell membrane 10 permeation. CNS penetration is also significantly reduced by increasing MW, with an analysis of 3059 diverse molecules clearly demonstrating that molecules with

MW < 300 Da on average having a 220´ higher brain/blood ratio than compounds with 10 MW > 700 Da.

With such significant problems associated with compounds that possess excessive

MW there must be an explanation as to why so many compounds fall into this known region of chemical space. Such an over-representation of high MW compounds in both drug discovery screening collections and the drug development process is largely due to a drive towards increased potency.15 One of the easiest ways potency can be gained is by increasing the number of non-specific interactions made between the

compound and the biological target. This is frequently achieved through the addition of lipophilic groups, and was termed molecular obesity by Hann in a review on the matter.15 This produces the desired potency increase whilst concomitantly increasing

MW and lipophilicity.

1.4.2. Lipophilicity Lipophilicity refers to the ability of a compound to dissolve in non-polar media, and is often measured by logP, which is the logarithm of the partition coefficient of the compound between water and n-octanol. Several computational methods exist for estimating lipophilicity values for organic compounds.16 Among these, the clogP and AlogP methods are the most widely used.16 These refer to compound logP (calculated using experimental values for smaller compounds and modelling using regression techniques) and atomic logP (addition of individual atomic logP contributions),16 respectively. The use of logP should only be used for compounds that are neutral at physiological pH. For compounds that contain ionisable functionalities that are likely to be charged at physiological pH, the term logD should be used where the aqueous phase is adjusted to a specific pH through the addition of a buffer.

Excessive lipophilicity has a major impact on the behaviour of compounds in the body, being linked to decreased biological solubility, increased plasma protein binding, increased brain protein binding and increased cytochrome P450 enzyme inhibition.10 Many of these issues are a result of non-specific interactions with undesired biological species. This is because logP (or logD) essentially represents the key events of molecular desolvation from aqueous phases to cell membranes and protein binding sites, which are generally hydrophobic in nature.17 A compound that possesses a high logP (or logD) may readily pass through cell membranes due to a low energy penalty to remove waters of hydration from the compound, hydrophobic interactions between the compound and the aqueous environment, and lipophilic interactions between the compound and the lipophilic cell membrane, but it may also bind to a variety of protein binding sites through the same non-specific driving forces. Analysis of 2133 drugs and reference compounds from the Cerep Bioprint database has shown that biological promiscuity increased dramatically as compound clogP exceeded 3.17 Further

evidence came from a study of 245 preclinical Pfizer compounds which also showed that compounds with increased lipophilicity had a greater chance of toxicity due to off-target binding.18,19 Another set of proteins that are routinely screened are the cytochrome P450 isozymes, as they play a critical role in drug metabolism. Inhibition of these enzymes can lead to potentially dangerous drug-drug interactions. A screen of 7098 compounds against a subset of P450 isozymes showed on average, compounds possessing a clogP > 5 exhibited an almost 8-fold greater promiscuity than compounds possessing a clogP » 0.19

1.4.3. Polar Surface Area (PSA) The polar surface area of a compound is the surface area in Å2 that is occupied by atoms of polar functionality. The importance of PSA in drug discovery has been highlighted by the analysis of in vivo studies involving 245 Pfizer preclinical compounds.18 It showed the effect lipophilicity and PSA can have on the probability of a toxicological outcome, which gave rise to the Pfizer 3/75 rule.18 On average, compounds with a higher PSA were found to be less likely to result in a toxicological event. Desirable PSA ranges do however vary with the biological target. A PSA of generally less than 60–70 Å2 is appropriate for CNS-active compounds due to higher PSA-possessing compounds struggling to permeate the blood-brain barrier.20

1.4.4. Fsp3 The term Fsp3 is the number of sp3 hybridised carbon atoms/total number of carbon atoms in a molecule. It is frequently used as a measure of molecular complexity and indicative of a molecule’s 3-dimensionality.21 Low Fsp3 has been linked to promiscuity.19 Increasing Fsp3 was also found to result in a significant increase in solubility.21 On average, as compounds progress from the discovery phases to final drugs, their average Fsp3 increases by 31%.21 This illustrates that compounds with a higher Fsp3 are more successful in drug development, and that ‘hits’ emerging from drug discovery possess an Fsp3 that is, on average, significantly below optimal for further progression.21

1.4.5. Aromatic Ring Count The number of aromatic rings that a compound possesses has been linked to the success of that compound in the drug development process.22 A review of the impact of aromatic ring count on a variety of parameters including serum albumin binding and hERG inhibition showed that the fewer aromatic rings a drug candidate possessed, the more likely it was to successfully progress through future stages of development.22

1.4.6. Undesirable Functional Groups Over time a growing number of functional groups have been recognised as being of concern within medicinal chemistry, unless such functionality is required by the compound’s mode of action. One such class are functionalities that are highly electrophilic, due to the potential for reactivity with biological nucleophiles such as DNA or proteins, or undergo hydrolysis by water to yield undesired products. Other medicinally-undesirable classes are functionalities that are known toxicophores, are redox-active, strongly coordinate metal ions, are aggregators or frequently generate false positives in screening.23,24

These physicochemical properties have a significant effect on how likely a compound is to proceed through future drug development stages. The next section details how these studies have resulted in the development of physicochemical guidelines for use within drug discovery and development.

1.5. Physicochemical Guidelines for Drug-Like Compounds Despite numerous physicochemical property values/ranges for small molecule drugs being linked to an increased probability of toxicological failure, data suggests that these warnings may not have been heeded yet. Various recent analyses (published between 2013 and 2015) of small molecules in drug discovery libraries revealed that they contained large proportions of compounds that deviated from such advice.3,25,26 For example, the issue of excessive compound size and lipophilicity is currently a widespread topic within the drug discovery industry.15,17,27 This is because whilst excessive size and lipophilicity are linked to several negative effects, adding lipophilic groups onto a compound is generally linked to increased potency and cell

permeability.15,28 This results in the drive towards increased potency yielding excessively large and lipophilic compounds. This appears to be a growing issue, with the size of oral drug compounds having increased dramatically over the last 40 years.17,27

This implies that a greater awareness is required towards the effect of physicochemical properties on the probability of drug development success. To this end, it would be beneficial to drug discovery efforts for knowledge on the subject to be compiled and made easily accessible, to be used to reduce toxicology-based attrition.

In 1997 Lipinski and co-workers published a “Rule of 5” for drug discovery that offered guidelines for physicochemical properties that could improve the probability of oral bioavailability.11 The guidelines were based on a study that compared the physicochemical properties of two libraries of compounds; one contained the > 50,000 drugs and pharmacologically-active compounds present in the World Drug Index (WDI), and the other was a subset the WDI that had progressed to Phase II clinical trials. The differences in the data sets resulted in the following guidelines being developed to direct compounds towards oral bioavailability, by stating that poor absorption or permeation are more likely when:

MW > 500 Da clogP > 5 HBD > 5 HBA > 10 The “Rule of 5” guide has been widely used to analyse existing compounds as well as guide ongoing drug discovery projects towards compounds that are statistically more likely to be successful. Whilst hugely successful, the “Rule of 5” has a number of limitations and exceptions. The “Rule of 5” was designed for orally administered drugs, and so is not applicable for compounds administered through alternative means (e.g. intravenously, inhalation). Also, many successful drugs possess physicochemical properties that lie outside the “Rule of 5” area.29

The “Rule of 5” guidelines were aimed at compounds that were of small molecule drug-like size: approximately 400–500 Da. As a result, the idea was particularly applicable towards the screening of compound libraries that produced ‘hits’ of small molecule drug-like size. However, there are prominent compound library construction approaches that acknowledge the benefits of screening smaller compounds, namely Lead-Oriented Synthesis (LOS) and Fragment-Based Drug Discovery (FBDD). These approaches generate compounds that are smaller than typical drug-like compounds, and so the “Rule of 5” is not applicable for the hits produced by these techniques.

1.6. Compound Library Construction Approaches Once a biological target has been identified and validated as being druggable, the next step is to identify compounds that bind to the biological target and elicit the desired biological response. These initial compounds are termed ‘hits’ and are frequently identified using high throughput screening (HTS). HTS is a drug discovery technique that obtains ‘hits’ through the automated assaying of a large compound library in an in vitro assay, and is commonly defined as achieving a screening rate of greater than 10,000 compounds per week.30,31,32,33 Such high screening rates are commonly facilitated by the use of 96-, 384- and 1536-well plates.30,31,32,33 The following sections detail some key approaches used to generate libraries of compounds for use in biological screening.

1.6.1. Combinatorial Chemistry Combinatorial chemistry can be defined as the systematic and repetitive connection of various building blocks through covalent bonds to generate a large library of diverse molecules.34 Initially, this approach generated huge ‘random’ libraries which primarily comprised of large and complex compounds, akin to small molecule drugs or natural products (Figure 8).31 The physicochemical properties of such resulting compounds were frequently undesirable due to overloaded molecular complexity.31 As a result, there has been a clear trend towards the generation of smaller libraries containing more focussed “drug-like” subsets.31

Whilst not exclusive to libraries resulting from combinatorial chemistry, the sampling of compounds comparable in size to small molecule drugs generates an issue in drug discovery. Utilising compounds of drug-like size and complexity results in an enormous amount of potential chemical space, with estimations ranging 1033–1063 potential drug-like compounds.35,36 This means that large libraries (often around 106) are required, but even then only a tiny percentage of drug-like chemical space is being sampled.

An advantage of using such compounds is that ‘hits’ can be identified with relatively insensitive equipment.37 Due to their size and complexity, there are usually many ways in which the compounds can interact with the biological target, resulting in ‘hits’ frequently possessing µM potency which are easily detectible. These hits, whilst moderately potent, often bind inefficiently to the biological target. To measure and compare binding efficiency, the metric ligand efficiency was developed.38,39 Ligand efficiency was defined as the average binding energy per non-hydrogen atom.37,38,39

Drug-like compounds

Biological target

Biochemical assay hit identification

Compound optimisation

Figure 8: Screening of small molecule drug-like compounds against a biological target

1.6.2. Lead-Oriented Synthesis (LOS) The amount of potential chemical space available to a library of compounds increases dramatically as the size and complexity of the compounds within that library increases, and it has been estimated40 that for every heavy atom added the number of biologically-relevant potential structures increases by a factor of 10. Such a relationship means that an assay that utilises smaller, less complex compounds requires a smaller compound library to sample a given fraction of chemical space. An alternative way to view it is that for a set library size, the smaller the compounds are in the library, the larger the fraction of chemical space the library samples. With this principle in mind, lead-oriented synthesis utilises compounds that are smaller and less complex than drug-like compounds, with a MW generally 200–350 Da (14–26 heavy atoms).40 These molecules are termed lead-like compounds.40 Using the previously mentioned heavy atom estimation,40 there are approximately 107 fewer potential biologically-relevant molecules with a mass ~300 Da (lead-like) than ~400 Da (drug-like). Lead-like compounds therefore sample chemical space more efficiently than drug-like compounds.

Lead-oriented synthesis (LOS) generates libraries of lead-like compounds which are then screened against a biological target to obtain ‘hits’ which elicit the desired physiological response (Figure 9). Typical optimisation within drug development observes a relationship whereby an increase in MW generally produces a concomitant increase in lipophilicity, as illustrated by the diagonal arrow in Figure 10. Therefore, a region of lead-like chemical space was defined by Churcher and co-workers, which was located such that compounds within it were predisposed to generate molecules within desirable drug-like chemical space through typical optimisation (Figure 10).40 In addition to this, Churcher and co-workers developed guidelines which stated that lead-like compounds should ideally possess:40

• 14 ≤ heavy atoms ≤ 26 (MW = 200–350 Da) • –1 ≤ clogP ≤ 3 • Chemically reactive, electrophilic or redox active groups removed • Favour molecules with lower degree of aromatic character • Favour molecules with more 3-dimensional shape

These guidelines help ensure that the lead-like compounds entering biological screening possess desirable molecular properties to maximise the probability of successful drug development.

Lead-like compounds

Biological target

Biochemical assay hit identification

Compound optimisation

Figure 9: Drug discovery through screening of lead-like compounds against a biological target

Limits of "Lipinski Rule of 5" chemical space 5

4 Optimal drug-like space

2 clogP optimisation 1 typical 0 Lead-like space −1 0 100 200 300 400 500 Molecular weight (Da) Figure 10: The regions of desirable lead-like and drug-like chemical space as defined by Churcher and co-workers40

Hits found through screening lead-like compounds are likely to be less potent but possess greater ligand efficiency than hits obtained from screening drug-like compounds. The lower potency of leads from LOS means that more sensitive detecting equipment may be required. A current challenge for LOS is the limited methodology to synthesise small, polar compounds, particularly ones which possess a variety of functionalities for use as either potential pharmacophores or for further derivatisation.40

1.6.3. Fragment-Based Drug Discovery (FBDD)

Fragment-based drug discovery uses low MW compounds (MW = 150–300 Da, < 20 heavy atoms) called fragments to probe for binding interactions with a biological target (Figure 11). Due to their low molecular weight, fragments sample chemical space even more efficiently than lead-like compounds. Calculations into the size of fragment chemical space have been conducted by the Reymond group.41,42 Through systematically and computationally enumerating all possible molecules containing up to 17 heavy atoms, just over 16.6 ´ 1010 possibilities were calculated. Whilst this number may appear very large, it is a miniscule fraction of the 1033–1063 estimated possible drug-like compounds.35,36 Fragments possess a size that benefits from being small enough that a library can sample chemical space efficiently, whilst being large enough to contain enough molecular complexity to form complementary, specific interactions with a biological target. Given that an increase in MW generally produces a concomitant increase in lipophilicity during drug development, fragment-like chemical space is located so that compounds within it are predisposed to generate molecules that lie within desirable lead-like and drug-like chemical space through typical optimisation (Figure 12).

The smaller size of fragments (relative to lead-like and drug-like compounds) means that they are generally able to form fewer interactions with the biological target, leading to lower binding affinities. Millimolar or high micromolar affinity is common and therefore higher assay sensitivity is required for FBDD.23 Fragment binding is usually detected through X-ray crystallography, surface plasmon resonance and NMR spectroscopy techniques. Despite their relatively weak binding potencies, ligand

efficiencies of fragment hits are generally higher than those of lead-like or drug-like compound hits.

Fragments

Biological target

Biochemical assay hit identification

+ +

Compound optimisation

Figure 11: Screening fragments against a biological target and optimisation of the ‘hits’

Limits of "Lipinski Rule of 5" chemical space 5

4 Optimal drug-like space

2 clogP 1 optimisation typical 0 Lead-like space −1 Fragment space 0 100 200 300 400 500 Molecular weight (Da) Figure 12: Typical regions of chemical space for fragment, lead-like and drug-like compounds as defined by Churcher and co-workers40

A current challenge for FBDD is the difficulty to synthesise small, polar fragments that also possess novelty and a variety of functionalities for potential pharmacophoric

activity or further elaboration. The limited methodology available which grants access to these compounds restricts FBDD.23,43

Fragment ‘hits’ can be optimised by growing one hit in a logical manner, or fragment linking can be utilised if two or more hits have been found to bind in proximal sites of the biological target.

To help ensure that fragment ‘hits’ possessed suitable physicochemical properties to be optimised into a desirable drug-like compound, in 2003 Astex developed physicochemical property guidelines for fragments.44 These guidelines stated that fragments should ideally possess:

• MW ≤ 300 Da • clogP ≤ 3 • HBD ≤ 3 • HBA ≤ 3 • Number of rotatable bonds ≤ 3 • Polar surface area (PSA) ≤ 60 Å2

This was elaborated 13 years later when Astex published an updated guide to fragment properties, based on the physicochemical properties of the Astex collection:23

• 140 ≤ MW ≤ 230 Da • 0 ≤ clogP ≤ 2 • 0 ≤ freely rotatable bonds ≤ 3 • 0 ≤ number of chiral centres ≤ 2 • Synthetic tractability. 50–100 mg and ≤ 4 synthetic steps from commercially available reagents • 3-Dimensional shape • Multiple synthetically accessible vectors for 3-dimensional fragment growth

This latter publication highlighted some current challenges in the design and synthesis of fragments.23 The first was that it is often difficult to synthesise and isolate fragments

that possess high aqueous solubility and polar functionality, which are desirable characteristics for fragments. There are also insufficient synthetic methods compatible with multiple heteroatoms and polar hydrogen-bonding functionality. Finally, it was noted that there is also a lack of methods that allow the incorporation of 3-dimensional architecture.23 These conclusions indicate that there needs to be significant methodology development aimed at synthesising small, polar, 3-dimensional compounds suitable for FBDD. The conclusions drawn by Astex employees echoed those from Goldberg and co-workers at AstraZeneca, highlighting that the challenges for FBDD are widely recognised and the solutions widely sought.25

Over the past 20 years FBDD has grown from a niche area of research to a main drug discovery approach and an important alternative to combinatorial techniques.45 Still being a relatively young approach, it is extremely encouraging that 2011 and 2016 have seen the first FDA approvals for drugs discovered through FBDD. The first was PLX4720, named Zemurafenib (Zelboraf®), a selective inhibitor of oncogenic B-Raf kinase which displays potent antimelanoma activity (Figure 13).46 PLX4720 inhibits V600E V600E B-Raf with an IC50 of 13 nM, with B-Raf being the most frequent oncogenic protein kinase mutation known. In phase I clinical trials, a remarkable 81% response rate in metastatic melanoma was observed.47 This example exemplifies how rapidly FBDD can enable a program, with the drug taking just six years to reach approval. The second drug was ABT-199, named Venetoclax (Venclexta™), a first-in-class BCL-2-selective inhibitor (Figure 13).48 The BCL-2 protein was the first identified major apoptotic regulator and plays a key role in tumorigenesis and chemoresistance.49 The apoptotic process is controlled by the dynamic binding interactions of proapoptotic and prosurvival proteins, and shifting the balance towards the latter is a known mechanism by which cancer cells undermine the normal apoptosis mechanism and gain a survival advantage.48,49 Proteins in the B cell CLL/lymphoma 2 family are key regulators of the apoptotic process, with the BCL-2, BCL-XL and BCL-W proteins being examples of prosurvival proteins.48,49 A previous compound which ABT-199 was based upon,

Navitoclax, selectively inhibited both BCL-2 and BCL-XL, however despite showing clinical efficacy in some BCL-2-dependent haematological cancers, the on-target

BCL-XL inhibition induced thrombocytopenia (low blood platelet count) which

drastically limited its use.48 ABT-199 on the other hand is highly selective, with a

Ki < 0.010 nM for BCL-2, a Ki = 48 nM for BCL-XL and a Ki = 245 nM for BCL-W. ABT-199 inhibits the growth of BCL-2-dependent tumours in vivo whilst having a 48 negligible effect on BCL-XL proteins, sparing human platelets. Venclexta™ was granted breakthrough therapy designation, priority review, accelerated approval and orphan drug designation.50

1st approved fragment-based drug 2nd approved fragment-based drug Zemurafenib (Zelboraf®) Venetoclax (Venclexta™)

F H N N Cl O O O O O N S F H NH N N S NO H N O 2 O Cl N NH

Figure 13: Structures for the 1st (Zelborafâ)46 and 2nd (Venclextaä) approved fragment-based drugs

The work described in this thesis was focussed on developing a synthetic strategy and methods that would allow ready access to a wide variety of structurally-related compounds for use within medicinal chemistry. Of critical importance would be the ability of this methodology to produce compounds with a variety of characteristics deemed desirable to medicinal chemistry, in an effort to reduce attrition within the drug discovery industry. These characteristics were: • Possession of 3-dimensional structure • Sample new areas of chemical space • Possession of desirable physicochemical properties • Synthetic tractability • A broad variety of functionality, including polar atoms and functionality capable of hydrogen-bonding • Utilise reliable, predictable, and high yielding reactions with broad substrate scopes

In order to achieve these objectives we aimed to utilise a cyclic scaffold which could be directly functionalised to create a diverse library of structurally-related compounds. The scaffold should possess multiple bond vectors that predisposes derivatives towards 3-dimensionality upon functionalisation. The cyclopropane ring has the potential to satisfy these criteria due to it being a low MW, conformationally rigid framework which may be built upon in multiple directions to give 3-dimensional derivatives. Furthermore, the cyclopropane ring is prevalent in medicinally-relevant, biologically active molecules, which will be the topic of the next section.

1.7. Cyclopropanes within Drug Discovery The cyclopropane ring is frequently found within natural products and pharmaceutical compounds,51 and is the 10th most commonly observed ring in small molecule drugs.52 These medicinally-relevant cyclopropane-containing compounds possess a wide range of biological activities, and are important in the treatment of a variety of diseases including asthma (Singulair),53,54 HIV (Efavirenz),55 diabetes (Saxagliptin),56 depression (Tranylcypromine)57 and cancer (Trametinib)58 to name a few (Figure 14).

Cl OH H2N O N O O HN F3C S H NEt2 Cl O O HO N O H

Singulair Milnacipran Efavirenz Tasimelteon Asthma Fibromyalgia HIV Insomnia

S OH O N N O H NH 2 O O N O N NH F HO N H N N H HN N N OH HO H2N C N N I F O F Ticagrelor Saxagliptin (±)Tranylcypromine Trametinib Heart attack/stroke Diabetes Depression Cancer Figure 14: Structures of some medicinally-important cyclopropane containing compounds. References: Milnacipran59, Tasimelteon60 and Ticagrelor.61

The cyclopropane ring provides a rigid framework for the 3-dimensional arrangement of substituents, allowing access to architecturally complex molecules. In addition to this, cyclopropane rings have found widespread use within medicinal chemistry as bioisosteres for a variety of functionalities.

Cyclopropane rings have been incorporated as replacements for alkyl chains such as methyl,62 ethyl,63 gem-dimethyl64 and iso-propyl65 groups to protect metabolically labile positions. An example of this was produced by Meanwell and co-workers, where incorporation of a cyclopropane ring increased the metabolic stability of the compound in human liver microsomes (HLM) by over a factor of 5 whilst retaining potency (Figure 15A).65

The cyclopropane ring can also act as an alkene bioisostere,66 to remove alkene-derived metabolic susceptibility whilst retaining conformational rigidity and similar bond vectors. Further bioisosteric potential has been demonstrated by using a cyclopropane ring to replace a phenyl ring, notably used to great effect in the development of Trametinib to reduce lipophilicity and aromatic ring count whilst simultaneously increasing potency (Figure 15B).67a Another relevant example is the use of a 1,1-disubstituted cyclopropane ring as a bioisostere for an ortho-substituted phenyl ring, giving a significant increase in potency (Figure 15C).67b

A) R 1 Metabolic stability O N R1 HLM t1/2 (min) EC50 (HEp-2) (µM) clogP N N i-Pr 7.4 0.004 2.21 N t-Bu 4.0 0.003 2.61 N c-Pr 39 0.010 1.72 c-Bu 4.6 0.016 2.28

O N O O N O H H N N N N

N N Cl Br O O clogP = 6.3 clogP = 5.0 IC50 (ACHN) = 4800 (68) IC50 (ACHN) = 1270 (5) IC50 (HT-29) = 990 (39) IC50 (HT-29) = 100 (2)

NMe2 F3C F3C NMe2 N N N N N N O O

OMe OMe

Ki (FXa) = 0.3 nM Ki (FXa) = 0.035 nM Figure 15: Use of the cyclopropane motif as a bioisostere in medicinally-relevant compounds. A) Comparison of bioisosteric alkyl groups in an effort to increase metabolic half-life.65 B) A section of the optimisation of Trametinib.67a Numbers in parentheses represent numbers of determinations. C) Use of a 1,1-disubstituted cyclopropane as an ortho-substituted phenyl mimic.67b

For the application of cyclopropanes as structural frameworks it is important to have reliable methodology that allows access to a wide variety of diversely functionalised cyclopropanes. Similarly, for use as bioisosteres there need to be reliable methods that allow the ready incorporation of a cyclopropane motif as a late-stage modification. For both of these purposes, novel methodology that allows the synthesis and direct functionalisation of cyclopropanes is of considerable interest to medicinal chemists.68 Next, some common approaches to the synthesis of functionalised cyclopropanes shall be discussed.

1.8. Common Methods to Synthesise Functionalised Cyclopropanes There are a number of commonly employed methods to generate functionalised cyclopropanes including Michael-initiated ring closure, Simmons-Smith cyclopropanation, carbene insertion into an alkene and cross-coupling of a cyclopropyl-organometallic species.

1.8.1. Michael-Initiated Ring Closure (MIRC) MIRC is a major method of cyclopropane synthesis which proceeds by a nucleophile undergoing Michael addition to form an enolate which then undergoes ring closure to release a leaving group. Possibly the most utilised of these MIRC reactions is the Corey-Chaykovsky cyclopropanation which utilises sulfur-based ylides.

The Corey-Chaykovsky cyclopropanation was developed in 1962 and involves a sulfur-based ylide that initially acts as a carbon-centred nucleophile, attacking an electron-deficient alkene (Scheme 2A).69 This is followed by ring closure with the ylide-carbon now acting as an electrophile. Due to the two-step nature of this approach, it is often observed that the stereochemistry of the reactant alkene is lost due to free C-C bond rotation in the enolate intermediate. The sulfur ylide is generally either dimethylsulfoxonium methylide (1) or dimethylsulfonium methylide (2). Dimethylsulfoxonium methylide (1) has much greater thermal stability and was found to preferentially undergo cyclopropanation when exposed to a,b-unsaturated carbonyl compounds in contrast to dimethylsulfonium methylide (2) which must be handled at around –10 °C and preferentially forms epoxides (Scheme 2B).69 More functionalised sulfur-based ylides can be utilised, producing cyclopropane products that possess increased functionality (Scheme 2C).70 This example also shows that non-Michael acceptor electrophiles can be used, providing the alkene is sufficiently electron-deficient.

H C H C 3 3 O O S CH or S CH2 + H3C 2 R O H3C R 1 2

O O O H3C R R O n = 0, 1 S CH H3C + S H3C 2 H C S H3C CH3 O n = 0, 1 3 R O n = 0, 1

B) Corey and Chaykovsky (1962)

H3C H3C S CH S CH2 H3C 2 H C O O O O 3 1 2

81% 89%

C) Taylor (2008)

BF4 EWG = COR', CO R', nitrile, i-Pr NaH (1.2 equiv) 2 R + SO2Ph , NO2 EWG S i-Pr R i-Pr DMF, 0 ºC-rt EWG R = alkyl, aryl, carbonyl, vinyl O (1.2 equiv) Scheme 2: Utilisation of sulfur-based ylides in cyclopropanation reactions

Enantioselective variations of the Corey-Chaykovsky cyclopropanation are rare, but a number of methods have been developed, generally utilising either a chiral sulfur ylide, an organocatalyst or a metal complex (Scheme 3). Tang showed that camphor-derived sulfur ylides can be used to obtain both high enantioselectivity and diastereoselectivity, yielding a variety of vinyl cyclopropanes (Scheme 3A).71,72 The observed selectivity was attributed to hydrogen bonding between the camphor alcohol and the alkene substrate.72 MacMillan developed an asymmetric organocatalytic cyclopropanation which utilised an iminium intermediate, activating the ylide by making it more electron-deficient and activating the enal substrate through a proposed electrostatic activation and stereodirected protocol (Scheme 3B).73 Shibasaki reported the use of a catalytic asymmetric La–Li3–(biphenyldiolate)3 + NaI system, that with 20 mol% of catalyst produced bifunctional cyclopropanes in excellent yields and enantioselectivities (Scheme 3C).74

A) Tang (2002, 2006) t-BuOK Br CO Et CO Et CH3 (3.0 equiv) 2 2 CO Et S TMS Ph 2 THF, -78 ºC OH Ph TMS Ph TMS 2-4 h 3 4 (1.2 equiv) 75% yield 3:4 = >99:1 97% ee B) MacMillan (2005)

CO2H N H O 20 mol% O S

CHCl3, -10 ºC O 24-48 h (4.0 equiv) O 73% yield 33:1 dr 89% ee C) Shibasaki (2007) Li * O O * O La O Li O O Li * 5 mol% O O NaI (5 mol%) O O H3C S * = H C CH O O 3 2 THF:toluene = 4:5 O 4 Å MS, -55 ºC, 18 h (1.2 equiv) 96% yield 99% ee Scheme 3: Enantioselective examples of Corey-Chaykovsky cyclopropanation reactions

Various other heteroatom-based ylides have also been shown to be effective cyclopropanating agents. Phosphorus-based ylides can be utilised towards cyclopropane synthesis (Scheme 4A) however they generally only give moderate yields, and like sulfur-based ylides their reactions generally proceed with low stereoselectivity.75 Arsenic-based ylides are another alternative, with Shen showing that excellent yields and stereoselectivities can be obtained (Scheme 4B).76 It was observed that the stereoselectivity of the cyclopropanation reduced when more electron-rich olefins were used. Tellurium-based ylides can be effective for the diastereoselective and enantioselective synthesis of vinyl cyclopropanes, as shown by Tang.77 The diastereoselectivity could be tuned by the reaction conditions such that two highly enantioenriched diastereoisomers, 5 and 6, could be obtained using the same tellurium ylide (Scheme 4C).

A) Bestmann (1965)

Br CH3 Ph3P CO2Et CO2Et NaNH2

Me Benzene, Δ, 12 h Me Me 50%

B) Shen (1986)

1) n-BuLi (1.33 equiv) O Si(Me)3 THF, -70 ºC - 20 ºC (Ph)3As Br 2) O (1.33 equiv) (Me) Si Cl 3 Cl 96% yield

C) Tang (2003)

CO2Me CO2Me BPh4 Conditions

Te Si(Me)3 CO2Me Me Si(Me)3 Me Si(Me)3 (2.5 equiv) Me 5 6 THF, 4–5 h

Conditions Yield (%) 5:6 ee (%)

LiTMP/HMPA 88 98:2 97

LDA/LiBr 98 3:97 83

Scheme 4: MIRC reactions using phosphorous, arsenic and tellurium-based ylides

Ammonium ylides have been shown to be valuable reagents for cyclopropanation reactions, with Gaunt developing both a stoichiometric and a catalytic “one-pot” ammonium ylide-based cyclopropanation utilising the tertiary amine DABCO (Scheme 5A).78 This included a preliminary study into a stoichiometric enantioselective variant, which was later developed to utilise sub-stoichiometric amounts of the chiral amine (Scheme 5B).79

A) Gaunt (2003) Ph O

O N O O Na2CO3 O Cl N S Ph Ph MeCN, 80 ºC, 24 h S O 0.2 equiv 1.5 equiv Ph 63% yield >95:5 dr

B) Gaunt (2004) MeO MeO N

N 20 mol% Ph O

O O Cs2CO3 (1.3 equiv) Br O Et2N Ph MeCN, 80 ºC, 24 h

(1.1 equiv) NEt2 94% yield 97% ee Scheme 5: Ammonium ylides in cyclopropane synthesis

1.8.2. Simmons-Smith Cyclopropanation A significant route to access cyclopropanes is through exposure of an alkene to a zinc carbenoid which provides a stereospecific route to the 3-membered carbocycle. This approach was first reported by Simmons and Smith in 1958 and it has received much attention since then.80 The Simmons-Smith cyclopropanation is proposed to proceed through a “butterfly” transition state which involves multiple bonds breaking and forming simultaneously (Scheme 6).81 This proposed transition state is consistent with the observed retention of configuration for these cyclopropanations.

I ZnI C I ZnI H2 ZnI2

"Butterfly" transition state Scheme 6: Simmons-Smith cyclopropanation via proposed “butterfly” transition state

The presence of a proximal hydroxyl group has been shown to greatly improve the yield of the cyclopropanation reaction whilst also increasing stereoselectivity by the

alcohol directing the zinc carbenoid to one face of the alkene preferentially (Scheme 7).81,82,83,84

OH Zn/Cu OH OH CH2I2

(syn) (anti)

67% yield >99% syn Scheme 7: Stereoselective cyclopropanation directed by a proximal alcohol84

A modified procedure was developed by Furukawa and co-workers which involved the 85,86 use of Et2Zn instead of zinc metal (Figure 16). This modification produced a homogeneous zinc carbene formation and allowed the reaction to be carried out in previously incompatible solvents (e.g. non-coordinating solvents).85,86 Denmark and co-workers have explored the reactivity of bis(halomethyl)zinc carbenoids,87 with the chemistry being developed further to generate enantioenriched cyclopropanes.88,89,90 Shi and co-workers have published the synthesis and utilisation of a class of tuneable zinc carbenoids primarily based on zinc carboxylates.91 The zinc carbenoid derived from trifluoroacetic acid was particularly effective in the cyclopropanation of a broad range of olefins.91 Charette and co-workers developed a synthesis for a readily prepared iodomethylzinc phosphate carbenoid as a powerful cyclopropanation tool.92 This approach lent itself to the incorporation of a chiral phosphate moiety, enabling enantioselective cyclopropanation.92

O O I Zn I Zn CH I Zn I I 3 I Zn I Zn P OEt O CF3 O OEt Simmons-Smith Furukawa Denmark Shi Charette Figure 16: A variety of zinc carbenoid cyclopropanation reagents

A variety of asymmetric approaches utilising zinc carbenoids have been developed, making use of either chiral auxiliaries or chiral ligands. Exploiting the former, in 1991 Charette and co-workers developed an asymmetric cyclopropanation that utilised a chiral non-racemic sugar auxiliary to induce asymmetry (Scheme 8).93 The desired

enantioenriched cyclopropane could be obtained by the removal of the auxiliary through a two-step procedure.

OBn OBn H Et2Zn, CH2I2 1. Tf2O, pyridine HO BnO O BnO O Ph O O BnO toluene BnO 2. pyridine, DMF, H2O OH Ph OH Ph H >97% yield 87% yield dr = 130:1 (over 2 steps) 98% ee Scheme 8: Asymmetric cyclopropanation using a zinc carbenoid and a sugar chiral auxiliary93

Charette’s group also developed an enantioselective cyclopropanation procedure utilising an enantioenriched dioxaborolane auxiliary (Scheme 9).94 A transition state was proposed where the boron coordinated to the allylic alcohol, with an amide carbonyl directing the carbenoid to the olefin resulting in facial selectivity. However, the stoichiometric amount of chiral species required for a chiral auxiliary approach is undesirable and the development of catalytic systems utilising enantioenriched ligands have generally been considered more attractive.

O O

Me2N NMe2

O O B Bu (1.0 equiv)

Zn(CH I) (2.0 equiv) Ph OH 2 2 Ph OH CH3 CH2Cl2, 0 ºC − rt CH3 96% yield 85% ee Scheme 9: Enantioselective Simmons-Smith cyclopropanation using an enantioenriched dioxaborolane ligand94

The first catalytic enantioselective Simmons-Smith cyclopropanation of an allylic alcohol was achieved by the Kobayashi group, who used a chiral, non-racemic disulfonamide-based Lewis-acid catalyst (Scheme 10).95 The initial publication showed that while the approach was successful in generating enantioenriched cyclopropanes, the yields and ee’s varied significantly with the structure of the olefin. Denmark optimised the system further, showing that reaction set-up was critical, resulting in conditions that were less sensitive to the reactant olefin structure.88,89,90

O2N NO2

S NH HN S O O O O (0.12 equiv)

Et2Zn (2.0 equiv) 1 1 CH2I2 (3.0 equiv) R = Ph R = BnOCH2 R1 OH R1 OH 82% yield 70% yield CH2Cl2, −23 ºC, 5 h 76% ee 36% ee Scheme 10: The first reported catalytic enantioselective Simmons-Smith cyclopropanation95

Charette and co-workers developed an asymmetric titanium-based Lewis-acid catalyst (Scheme 11).96 This titanium-based catalyst provided very high enantioselectivities for aryl substituted allylic alcohols however was less effective for alkyl substituted variants.96,97

O O Ph Ph Ph Ph O O Ti i-PrO Oi-Pr (0.25 equiv)

Zn(CH2I)2 (1.0 equiv) Ph OH Ph OH CH2Cl2, 0 ºC, 1.5 h 80% yield 90% ee Scheme 11: Titanium-based Lewis acid catalysis towards cyclopropanes by Charette and Brochu96

1.8.3. Diazo Compound-Derived Carbene Insertion into an Alkene The condensation of diazo compounds with alkenes as a cyclopropanation approach has been known for over 100 years.98 These early cyclopropanation reactions were thermally promoted, often requiring temperatures of ~150 °C.99,100 The high reaction temperatures combined with the exothermic nature and the concomitant gas evolution made these reactions unpredictable and often violent. Silberrad and Roy demonstrated that diazo compound decomposition could be catalysed by a transition metal in 1906.101 Early reports of transition metal catalysts being utilised for cyclopropanation reactions include that by Stork and Ficini in 1961, where insoluble copper bronze was used as a catalyst.102 Heterogeneous transition metal catalysts

dominated cyclopropanation methodology until the development of soluble copper chelates, with notable examples being developed by Nozaki103 and by Moser.104 These homogeneous catalysts were perceived to be superior to their heterogeneous counterparts due to greater reliability and smoother reactions.103,104 Transition metal catalysed diazo decomposition is also a far safer method for diazo decomposition than the thermal alternative due to the much lower risk of explosion resulting from rapid stoichiometric nitrogen gas evolution.

Since the discovery of transition metal catalysis for diazo compound-derived carbene insertion into an alkene, a wide range of transition metals including Cu,105 Rh,106 Ru,107,108 Pd,109 and Co110,111 have been shown to be successful at this reaction. A variety of mechanisms for transition metal-catalysed cyclopropanations have been proposed, with the main factor dictating which mechanism is in operation being the transition metal.

The most prevalent mechanism involves the formation of an electrophilic carbenoid species from the transition metal catalyst and the diazo compound, which then reacts with an electron-rich alkene to form the cyclopropane product (Scheme 12). This mechanism was first proposed by Yates in 1952 and was based upon observations made on the copper-catalysed decomposition of diazoketones.112 Cyclopropanations that proceed through an electrophilic carbene mechanism are generally stereospecific, occurring with retention of configuration. Transition metals that have been associated with this mechanism include copper,113 rhodium,113,114 ruthenium113 and chromium.115 Commonly, significant amounts of the corresponding maleate and fumarate side-products are produced, resulting from reaction of the electrophilic carbenoid with a molecule of diazo compound (Scheme 12).

N2 MLn R2 R1 R1 R2 R1 R1 R1 Examples of metals R1 R2 R3 associated with 2 2 R2 N2 R R electrophilic carbene mechanism: R3 N2 CuI, CuII, RhII, RuII, Cr0 R1 R2 R1 R2

N2 MLn Electrophilic carbene Scheme 12: Transition metal-catalysed cyclopropanation via an electrophilic carbene

This mechanism is supported by the widespread observation that electron-rich alkenes such as styrene derivatives are far more successful in these cyclopropanation reactions than electron-neutral or electron-deficient examples. Further support is provided by the detection and characterisation of carbene intermediates. Hofmann developed an iminophosphanamide ligand which stabilises otherwise elusive or labile copper coordination modes through a combination of enhanced metal-to-ligand back donation and steric shielding of the copper centre (Scheme 13).116 This copper 8 complex reacted with methyl 2-phenyl-2-diazoacetate in toluene-d , C6D6 or pentane at ambient temperature generating a single new copper complex 7 which was unambiguously identified by 1H, 13C{1H}, 29Si{1H} and 31P{1H} NMR spectroscopy (Scheme 13).117

SiMe SiMe3 t-Bu 3 CO Me N 2 t-Bu N P Cu P Cu MeO2C N t-Bu N t-Bu – N2 SiMe N2 3 SiMe3 – C2H4 7 Scheme 13: Synthesis of a stabilised copper carbene for spectroscopic identification116,117

The downfield 13C NMR signal observed for the ester carbonyl carbon in copper carbene complex 7 indicated the presence of an electrophilic carbon centre. Further evidence for copper carbene 7 possessing an electrophilic nature was obtained through analysis of the restricted rotation of the phenyl ring. The carbene carbon of 7 can only withdraw stabilising electron density from the phenyl ring p-system if orbital overlap is present, hence the energy needed to overcome restricted rotation is

influenced by the electrophilicity of the carbene carbon. Using variable temperature 1H NMR spectroscopy the coalescence temperature of the diastereotopic ortho-phenyl protons was measured to be –70 °C, and the corresponding rotational energy barrier was found to be in accordance with the carbene carbon atom possessing electrophilic character. The addition of styrene to solutions of the copper carbene complex resulted in an almost complete loss of spectroscopic signals from the copper carbene complex, and the styrene was cyclopropanated to give a mixture of trans and cis diastereoisomers. This provides strong support for copper carbenes being present in copper-catalysed cyclopropanation reactions. In this same work, the iminophosphanamide chelate ring and the carbene plane were found to be mutually orthogonal, with a Cu=C rotational barrier of at least 60 kJ mol-1; information that is highly valuable in the pursuit of designing ligands which exhibit stereoselectivity over the cyclopropanation reaction.

In a recent publication, Fürstner has shown that by using a bis(4-methoxyphenyl) carbene backbone to impart meta-stability onto highly reactive intermediates, a rhodium carbene was able to be characterised by 1H and 13C NMR, IR, UV, HRMS and X-ray crystallography (Figure 17).118 In a similar observation to that made by Hofmann with a copper carbene, Fürstner observed a significantly downfield carbene carbon 13C NMR chemical shift, indicating the presence of a highly electrophilic carbene.118,119 The rhodium carbene was shown to be highly active in the cyclopropanation of 4-methoxystyrene and so appears to be a valid intermediate in the rhodium catalysed cyclopropanation of alkenes with diazo compounds.

CPh3

O O OMe CPh3 O O Rh Rh O O

Ph3C O O OMe

CPh3 Figure 17: Structure of an isolatable rhodium carbene synthesised by the Fürstner group118

A drawback with cyclopropanation reactions that proceed via the electrophilic carbene mechanism is that the diazo reagent can undergo dimerisation through a transition metal-catalysed side reaction, often producing significant amounts of the corresponding maleate and fumarate side-products (Scheme 12).120 This problem is often overcome by keeping only a low concentration of diazo compound in the reaction mixture through a combination of using the alkene in a significant excess, often as the solvent, and by slow addition of the diazo reagent. These modifications detract from the approach’s desirability due to the increased practical complexity, and especially if the alkene reactant is valuable.

In contrast to the electrophilic carbene mechanism which most transition metals employ, palladium is believed to utilise a mechanism that proceeds via a 4-membered palladacyclobutane intermediate which then undergoes reductive elimination to release the cyclopropane product (Scheme 14). This mechanism is supported by competition experiments which measured the relative ability of various 121 alkenes to undergo cyclopropanation with Pd(OAc)2, Cu(OTf)2 and Rh2(OAc)4. In contrast to Cu(OTf)2 and Rh2(OAc)4, it was found that Pd(OAc)2 preferentially reacted with strained or conjugated olefins, and that terminal alkenes were more reactive than internal isomers or homologues. In intramolecular competitions it was observed that the less substituted alkene was regioselectively cyclopropanated. These observations all suggest the operation of a mechanism that involves initial p-complexation to the olefin reactant, as opposed to an electrophilic carbene mechanism. DFT calculations of the palladium-catalysed cyclopropanation of alkenes by diazomethane have supported explanations of the behaviour and selectivity observed, as well as helped elucidate the most probable mechanism of the catalytic cycle (Scheme 14).122

Precatalyst

II Pd X2 8

CH2 Alkene coordination n N2 Precatalyst reduction CH Oxidation products 2 N2

Pd0 n 9

0 Pd 13 0 n–1 Pd CH2 10 n N2

Reductive elimination 12 II Pd N2 n–1 0 Pd CH2 n 11 Oxidative addition

Scheme 14: Pd-catalysed cyclopropanation mechanism

The PdII precatalyst (8) is reduced to Pd0 by the diazo reagent which is a transformation that has been frequently observed.123,124,125 Complexation of 2 diazomethane forms a Pd(h -C2H4)n(kC-CH2N2) complex (10) which then undergoes 2 elimination of N2 to generate a (h -C2H4)Pd=CH2 species (11). This species is critical to the nature of the catalytic cycle, as the transition metal complex contains both the carbene and the alkene to be cyclopropanated. Oxidative addition of the carbene with the coordinated alkene generates the corresponding palladacyclobutane (12), which then undergoes an extremely facile reductive elimination to generate the cyclopropane product. A potential alternative pathway which involves the attack of a non-coordinated alkene to the Pd carbene was calculated to possess a Gibbs free activation energy of 51.3 kJ mol-1, almost double the 28.1 kJ mol-1 calculated for oxidative addition involving the coordinated alkene. The catalytic cycle is completed with the coordination of another alkene, regenerating the starting Pd0 species (9).

The role of pallada(II)cyclobutane derivatives in Pd(OAc)2-catalysed cyclopropanation reactions is supported by the isolation and observed reactivity of this class of complexes. Possessing a bidentate nitrogen ligand, a pallada(II)cyclobutane

derivative has been structurally characterised.126 Such palladacycles exhibit facile reductive elimination to yield cyclopropane derivatives.126 The proposed palladium-based catalytic cycle is in accordance with the known propensity of coordinatively unsaturated palladium to complex alkenes.127

The third transition metal-catalysed cyclopropanation mechanism is a radical-based mechanism, and is known to be employed by CoII.128,129,130 CoII possesses a d7 d-configuration and when in a square-planar geometry is in the low-spin electronic configuration.129 One of the most notable observations with CoII-catalysed cyclopropanations is that it allows the cyclopropanation of electron-deficient alkenes. Another significant observation of cobalt-catalysed cyclopropanation reactions is the absence of diazo dimerisation products which means that an excess of alkene and a slow-addition protocol are not required. Both of these observations are in stark contrast to a mechanism that proceeds via an electrophilic carbene.

The observation that CoII-based cyclopropanations are very successful with electron-deficient alkenes suggests some nucleophilic character of the carbene transfer intermediate in these reactions. In a joint experimental and computational effort to identify the mechanism, the Zhang group used EPR spectroscopy to probe the radical in cobalt(porphyrin) complexes both before and after addition of 4 equivalents of EDA.128 Upon the addition of EDA there was complete conversion to three different paramagnetic species. One was assigned as a cobalt(porphyrin) complex coordinating a weak-field ligand (e.g. H2O), the second was assigned as the cobalt(porphyrin)(carbene) complex with the carbene bridging between the cobalt and a nitrogen of the porphyrin ligand, and the third was assigned as terminal carbene 14 (Figure 18) due to it being an organic radical which possessed hyperfine coupling to a hydrogen and cobalt. Using DFT methods the singly occupied molecular orbitals (SOMO) and spin density plots for the ‘bridging carbene’ and the ‘terminal carbene’ were calculated. According to these calculations the ‘bridging carbene’ radical resides primarily in the Co 3� orbital whereas for the ‘terminal carbene’ the radical lies mainly on the ‘carbene’ carbon and is delocalised slightly over the neighbouring cobalt and oxygen atoms. This strongly indicates that the carbene ligand is redox

non-innocent and accepts an electron via intramolecular electron transfer from the CoII centre.

Interaction between the singly occupied Co 3� orbital and the doubly occupied C 2�� orbital raises the energy of the Co 3� orbital above the p* orbital formed from overlap of the doubly occupied Co 3� orbital and the empty C 2� orbital (Figure 18). The half filling of the Co–C p* orbital substantially reduces the metal–carbon bond order, as has been observed experimentally.131 This also accounts for why the carbene species loses typical Fischer-type character, gains radical-type behaviour and becomes more nucleophilic.

O O H H OMe OMe N N N N Co Co N N N N

SOMO

2 2 3dz 3dz π* SOMO

2py 2py

3dyz 3dyz π

Co C Co C

Figure 18: Simplified molecular orbital diagram for redox non-innocent behaviour of CoII(porphyrin)(carbene)128

With this information in combination with mechanistic DFT studies, a catalytic cycle was proposed (Scheme 15).128

R1 H R1

N2 R2 II LnCo

H R1 R2 H II LnCo R1 H III LnCo

H R1

III LnCo

H Scheme 15: CoII radical-based catalytic cycle for cyclopropanation

This catalytic cycle accounts for the differences observed between cyclopropanation reactions that are catalysed by cobalt and those catalysed by closed-shell transition metals. To support this mechanism, Zhang aimed to isolate a cobalt-carbene complex, however due to their high reactivity only decomposition products were isolated.129 It was hypothesised that a cobaltIII-carbene radical complex from ethyl styryldiazoacetate would be stabilised by resonance, and so may be more stable during isolation attempts. Upon incorporation of ethyl styryldiazoacetate with a cobalt(porphyrin) complex, a dimeric CoIII complex was obtained in a 90% yield, formed from the radical combination of two separate cobaltIII(porphyrin)(carbene) complexes.129

Significant advances have been made in the field of asymmetric cyclopropanation of electron-deficient alkenes through the utilisation of cobaltII(porphyrin) complexes.130,132,133,134 Whilst there are a limited number of examples of radical behaviour being observed with paramagnetic forms of the other group 9 metals rhodium and iridium, neither of these metals have yet produced cyclopropanation reactions that indicate a radical-based mechanism.135,136,137,138 It is relevant to note that the Co-catalysed cyclopropanation has occasionally been illustrated as proceeding via a four-membered cobaltocycle.139

In summary, utilising a wide variety of transition metals catalysts, diazo-derived carbene insertion cyclopropanation protocols have proved to be incredibly powerful in asymmetric cyclopropanation, a topic which will be covered in Section 2.1.4.

1.8.4. Cross-Coupling of a Pre-Functionalised Cyclopropyl-Species The cross-coupling of cyclopropanes bearing appropriate functionality offers a powerful route to functionalised cyclopropanes. As a method that can utilise a core cyclopropyl species and react it with a variety of partners, this approach offers a divergent route to a broad scope of functionalised cyclopropanes.

A wide range of cross coupling reactions are possible on a cyclopropane ring. Cyclopropyl Grignard species have been utilised in Kumada-Corriu cross-coupling reactions to produce aryl-substituted cyclopropanes (Scheme 16A).140 In addition, cyclopropyl zinc species have be used in Negishi cross-couplings141 and cyclopropyl stannanes can undergo Stille cross-coupling142 (Scheme 16B and 16C respectively).

A) [Pd(ligand)Cl2]2 (2 mol%) OMe AsPh3 (15 mol%) Br OMe ligand = MgBr THF, 60 ºC, 24 h OMe (1.5 equiv) MeO P Cl 84% t-Bu

B) Pd(dppf)Cl2 (5 mol%) SO2Me MeO2S CuI (6 mol%)

ZnCl Br CO2Me THF, rt, 3 h CO2Me (1.5 equiv) 70%

C) Pd(OAc) (5 mol%) AsPh3 (15 mol%) CuI (5 mol%) NMe2 NMe2 LiCl (3 equiv) I Me DMF, 80 ºC, 12 h Sn(n-Bu)3 (2.0 equiv) Me 63% Scheme 16: Cross-coupling reactions of a variety of cyclopropyl organometallic species

Suzuki-Miyaura cross coupling has been demonstrated on cyclopropyl boronic acids,143 boronic esters144 and trifluoroborate salts145 to generate a variety of aryl-substituted cyclopropanes. Cyclopropyl boronic acids have also been utilised in Chan-Lam cross couplings with anilines and amines to produce a broad range of cyclopropyl amines in excellent yields (Scheme 17A).146 Silicon-substituted cyclopropanes have been utilised in Hiyama-Denmark cross-coupling reactions as another route to aryl-substituted cyclopropanes in excellent yields (Scheme 17B).147

A) Cu(OAc)2 (1.0 equiv) Bipyridine (1.0 equiv) Na2CO3 (2.0 equiv) HN N Boc N B(OH)2 DCE, air, 70 ºC N Boc (2.0 equiv) 97%

B) OMe OMe 1) BF3⋅OEt2 (1.5 mol%) 2) Pd(PPh3)4 (5 mol%) TBAF (4.0 equiv) Br CF3 THF, 100 ºC, 17 h Ot-Bu Si Ot-Bu (1.0 equiv) OH CF3 92% Scheme 17: A) Chan-Lam and B) Hiyama-Denmark cross-coupling of cyclopropyl species

Cyclopropyl iodides can be used as cross-coupling partners, with an example being of a Sonogashira cross-coupling reaction, giving excellent yields of alkyne-substituted cyclopropanes (Scheme 18A).148 Cyclopropyl iodides have also been shown to be successful coupling partners in Suzuki-Miyaura cross-couplings, with Charette and Giroux demonstrating the synthesis of aryl- and vinyl-substituted cyclopropanes in excellent yields through this method (Scheme 18B and 18C respectively).149

A) PdCl2(MeCN)2 (3 mol%) CO2Me X-Phos (9 mol%) CO2Me Cs2CO3 (2.5 equiv)

toluene, 100 ºC, 1 h I (1.5 equiv) 98%

B) Pd(OAc)2 (10 mol%) PPh3 (50 mol%) K CO (3.0 equiv) OBn OBn 2 3 Bu4NCl (2.0 equiv) (HO)2B Cl DMF−H2O (4:1), 90 ºC I (1.5 equiv) Cl 83%

C) Pd(OAc)2 (10 mol%) PPh3 (50 mol%) K CO (3.0 equiv) OBn OBn 2 3 O Bu4NCl (2.0 equiv) B O DMF−H2O (4:1), 90 ºC I (1.5 equiv) 84% Scheme 18: A) Sonogashira and B), C) Suzuki-Miyaura cross-couplings using cyclopropyl iodides

Despite the various ways to synthesise cyclopropanes, there is a lack of methodology that allows the synthesis of a bifunctional cyclopropyl scaffold that can undergo divergent functionalisation to generate a wide range of cyclopropane-containing compounds.

1.9. Project Aims The research detailed in this PhD thesis aimed to develop methodology that allowed access to a diverse range of cyclopropane-containing compounds for use within medicinal chemistry through the divergent functionalisation of a readily accessible bifunctional cyclopropyl scaffold (Scheme 19). This methodology could then be used to generate libraries of cyclopropane-containing compounds in minimal synthetic steps.

functionalise A A R1 cyclopropanation functionalise B B R2

bifunctional medicinally-relevant cyclopropyl scaffold cyclopropanes Scheme 19: General plan for the divergent synthesis of bifunctional cyclopropanes

Functionalised cyclopropanes possess a rigid 3-dimensional structure which makes them attractive design elements in drug discovery. The cyclopropane ring can be utilised to great effect within medicinal chemistry as a core scaffold or as a bioisostere for a variety of functional groups. These attributes allow novel functionalised cyclopropanes to access new and pharmaceutically-significant areas of both chemical and intellectual property (IP) space. To achieve this the cyclopropyl scaffold requires functional handles that utilise the 3-dimensional bond vectors granted by the cyclopropane ring. The functional handles must also undergo orthogonal, divergent derivatisation.

A cyclopropyl scaffold possessing an ester and a sulfide was targeted (Scheme 20). This could potentially be synthesised by a transition metal-catalysed cyclopropanation of ethyl diazoacetate and phenyl vinyl sulfide. Synthesis of both trans and cis scaffold diastereoisomers would increase the shape diversity of the derivatised products (Figure 19). Once synthesised, the cyclopropyl scaffold could then undergo orthogonal derivatisation of the ester and sulfide functionalities, generating a wide variety of medicinally-relevant compounds. Functionalisation would proceed as to yield compounds with desirable physicochemical properties for use within drug discovery.

Reduction

Hydrolysis EtO C 2 Amidation N Transition metal 1 2 CO2Et R catalysis

SPh R2 SPh Oxidation bifunctional medicinally-relevant cyclopropyl scaffold Sulfoxide–metal exchange cyclopropanes then electrophilic trap

Sulfoxide–metal exchange then Negishi cross-coupling

Scheme 20: Synthetic plan for the divergent synthesis of bifunctional cyclopropanes

CO2Et CO2Et

SPh SPh 15 16

Figure 19: 3-Dimensional schemes of trans- and cis-substituted cyclopropanes 15 and 16, respectively

With these derivatisation reactions in mind, Figure 20 shows a range of bifunctional cyclopropanes that could potentially be synthesised through this approach, along with some of their calculated physicochemical properties.

O O N HO N O N O OH

N S S N O O N

MW = 180 MW = 308 MW = 298 MW = 216 AlogP = 2.74 AlogP = 0.16 AlogP = 1.98 AlogP = 1.35 HBD/HBA = 1/1 HBD/HBA = 0/5 HBD/HBA = 1/5 HBD/HBA = 0/3 Fsp3 = 0.400 Fsp3 = 0.53 Fsp3 = 0.35 Fsp3 = 0.54 PSA = 20.23 Å2 PSA = 57.69 Å2 PSA = 72.31 Å2 PSA = 33.20 Å2 Figure 20: Bifunctional cyclopropane-containing compounds potentially accessible through the planned approach

2. Results and Discussion 2.1 Transition Metal-Catalysed Cyclopropanation of Phenyl Vinyl Sulfide with Ethyl Diazoacetate Compounds (trans)- and (cis)-ethyl 2-(phenylsulfanyl)-cyclopropane-1-carboxylate (15 and 16) were targeted as bifunctional scaffolds that could undergo orthogonal derivatisation to yield a wide variety of cyclopropane-containing compounds for use within drug discovery. The planned route to these cyclopropanes was through a transition metal-catalysed cyclopropanation of PVS with EDA (Scheme 21). The thermally-promoted cyclopropanation of PVS and EDA had been reported once by Kaiser and co-workers in 1962.99 The reaction required extreme heating (100–170 °C) in a sealed vessel and gave a 76% yield of 15 and 16. There are considerable safety concerns with such extreme heating of diazo compounds, particularly in sealed vessels, due to the stoichiometric N2(g) evolution. In order to develop a safer reaction, transition metal catalysis was explored.

O EtO O EtO O catalyst S EtO Ph solvent Ph Ph N2 S S EDA PVS 15 16 Scheme 21: Synthetic scheme for proposed cyclopropanation to yield trans- and cis-cyclopropyl scaffolds

An analysis of prominent cyclopropanation literature showed that a large number of transition metals can be successfully utilised in cyclopropanation reactions between diazo compounds and alkenes. Exploration of some of the most prominent catalyst systems revealed that they were often based on CuI, CuII, RhII or PdII,150,151,152,109 which led to the investigation of these transition metals for the cyclopropanation of PVS with EDA.

The complexes CuOTf, Cu(OTf)2, Cu(acac)2, Rh2(OAc)4, Pd(OAc)2 and PdCl2 were tested for activity in the cyclopropanation of PVS with EDA. All complexes were stored in a desiccator except for CuOTf which was stored and handled in a glovebox. All reaction vessels were flame dried and purged with Ar(g) before use to eliminate any issues from O2 or moisture-based sensitivity any of the complexes may have, which if

not controlled thoroughly could cause erroneous results. PVS was vacuum distilled before use, and the diazo reagent was added as a CH2Cl2 solution via syringe pump over 8 hours. Initial investigations began using 0.5 mol% catalyst loading and with anhydrous CH2Cl2 as the solvent at 30 °C, as similar conditions have been frequently 150,151 utilised. At 30 °C only Cu(acac)2, CuOTf and Cu(OTf)2 generated cyclopropane products (Table 1, entries 4–6). Using CuOTf gave the highest yield out of the catalysts screened, and the observation that the catalysed cyclopropanation proceeded at a temperature as low as 30 °C was encouraging. The resulting cyclopropanes 15 and 16 were readily separated through silica chromatography and the diastereoisomers distinguished by their J-coupling constants in their 1H NMR spectrums. Typical 1 3 cyclopropyl H NMR coupling constants are in the ranges of Jtrans = 4.5-7.5 Hz, 3 2 Jcis = 7.5-11.0 Hz and Jgem = 4.5-7.0 Hz. As expected for a cyclopropanation that proceeded via an electrophilic carbene, dimerisation of EDA was observed generating diethyl maleate and diethyl fumarate side-products.

Table 1: Catalyst optimisation for the transition metal-catalysed cyclopropanation of PVS with EDA

O EtO O EtO O Catalyst (0.5 mol%) S EtO Ph CH Cl , 30 C N 2 2 ° Ph Ph 2 24–48 h S S 1.0 equiv 15 16

Entry Catalyst Solvent Yield trans + cis (%) a 1 Rh2(OAc)4 CH2Cl2 0 b 2 PdCl2 CH2Cl2 0 b 3 Pd(OAc)2 CH2Cl2 0 b 4 Cu(acac)2 CH2Cl2 5 b 5 Cu(OTf)2 CH2Cl2 4 b 6 Cu(OTf)·toluene CH2Cl2 33 a Cat. (0.5 mol%) added to flame-dried vial, sealed and flushed with Ar(g). A solution of phenyl vinyl sulfide (131 µL, 1.0 mmol) in CH2Cl2 (7.0 mL, 0.14 M) was added and warmed with stirring to 30 °C. A solution of ethyl diazoacetate (118 µL, 1.0 mmol) in CH2Cl2 (118 µL, 8.5 M) was added over 8 h and then stirred for a further 16 h. b Same method as for a but stirred for a total of 48 h.

2.1.1 Bomb Calorimetry of PVS, EDA and the Product Cyclopropanes To better understand the hazards associated with this cyclopropanation and to develop cyclopropanation conditions that operated at an acceptable temperature, bomb calorimetry of PVS, EDA and a sample of 15 and 16 was carried out. Bomb calorimetry of PVS showed a slight and gradual increase in temperature beginning at

59 64J-E13842-021-PVS Integrated

Author: METTLER METTLER Date: 4/16/2015 289 °C Daandtabas e: withSTA Re a D ef maximumault DB V12.00 A- atICT A:340 METT LE°CR which corresponded to exothermic decomposition of the substance (Figure 21). Evaluation: 64J-E13842-021-PVS Integrated, 16.04.2015 14:56:52

Figure 21: Bomb calorimetry data for phenyl vinyl sulfide Curve: 64J-E13842-021-PVS Integrated, 16.04.2015 15:05:26 Sample Name: 64J-E13842-021-PVS AuthMethodor: Name:METTLER MDSCETTLER Date: 4/16/2015 Bomb calorimetryTest Name: of EDADSC (Figure 22) showed a sharp increase in temperature Database: STARe Default DB V12.00 A-ICTA: METTLER Instrument Name: EW_DSC beginning at 99 °C and reachingDSC 1/700/2160, a 22.05.2013 maximum 11:59:08 at 120 °C which corresponded to rapid Evaluation:Run Date: 16.04.2015 15:05:26 exothermicReport decomposition. Date: 16-Apr-2015 15:07:10 Instrument Method: 40-450 C @ 10 C/min Gold (Safety Work) dt 1.00 s [1] 40.0..450.0 °C, 10.00 K/min Synchronization enabled Instrument Test Name: METTLER

- 1 / 1 -

Figure 22: Bomb calorimetry data for ethyl diazoacetate Curve: 64J-E13842-021-EDA, 15.04.2015 17:23:36 Bomb calorimetrySample Name: of a 1:164J-E13842-021-EDA mixture of 15 and 16 showed a very gradual decrease in Method Name: DSC temperatureTest Name: beginning DSC at 223 °C which corresponded to evaporation of the Instrument Name: EW_DSC compounds (Figure 23). DSC 1/700/2160, 22.05.2013 11:59:08 Run Date: 15.04.2015 17:23:36 Report Date: 16-Apr-2015 15:11:18 Instrument Method: 40-450 C @ 10 C/min Gold (Safety Work) 60 dt 1.00 s [1] 40.0..450.0 °C, 10.00 K/min Synchronization enabled Instrument Test Name: METTLER

- 1 / 1 - 64J-E13842-021-355-2 Integrated

Author: METTLER METTLER Date: 4/16/2015 Database: STARe Default DB V12.00 A-ICTA: METTLER

Evaluation: 64J-E13842-021-355-2 Integrated, 16.04.2015 14:57:40

Figure 23: Bomb calorimetry data for a 1:1 mixture of 15 and 16 Curve: 64J-E13842-021-355-2 Integrated, 16.04.2015 14:53:45 Sample Name: 64J-E13842-021-355 Method Name: DSC The bombTest calorimetry Name: dataDSC obtained illustrated how the various species in the Instrument Name: EW_DSC cyclopropanation reactionDSC behave 1/700/2160, 22.05.2013 at high 11:59:08 temperatures, confirmed that EDA is the Run Date: 16.04.2015 14:53:45 species in Reportthe Date:reaction mixture16-Apr-2015 15:09:11that is most sensitive to high temperatures, and also Instrument Method: 40-450 C @ 10 C/min Gold (Safety Work) dt 1.00 s provided insight into [1] the 40.0..450.0 onset °C, 10.00 K/mintemperature for thermally activated EDA Synchronization enabled decomposition.Instrument In Test ligh Name:t ofMETTLER this, the transition metal-catalysed cyclopropanation of PVS and EDA should be conducted at a reaction temperature that is significantly below 99 °C.

I 2.1.2. Cu -Catalysed Cyclopropanation- 1 / 1 - of PVS with EDA Copper has been used as a catalyst in cyclopropanation reactions for over 50 years, with an early report coming from Stork and Ficini in 1961 using copper bronze as a heterogeneous catalyst.102 Homogeneous copper catalysts emerged in the mid 1960’s, with notable independent examples from Nozaki103 and Moser.104 The first asymmetric, metal-catalysed cyclopropanation of diazo compounds was developed by Nozaki and utilised a copper catalytic centre with two chiral salicylaldimine ligands.153 Whilst the enantiomeric excesses observed were low, this seminal publication demonstrated that a homogeneous metal-catalysed reaction can be rendered enantioselective through the attachment of a chiral ligand to the metal centre. The addition of either a CuI or CuII source had been known to catalyse cyclopropanation

reactions of diazo compounds, however in 1985 Aratani provided significant evidence that the active catalyst in at least some CuII-based systems was actually a CuI species that had been generated through in situ reduction of the CuII source.154 This process often occurs through the heating of the CuII precatalyst and diazo reagent to 70–80 °C, evolving nitrogen as the reduction proceeds.154 Alternatively, the reduction can be effected through pre-treatment with a reducing agent such as phenylhydrazine at room temperature.105,154 To avoid the need for a CuII reduction step prior to cyclopropanation, the catalytically-active CuI salt or complex can be added directly. CuI species are, however, frequently more moisture sensitive than their CuII counterparts and are prone to disproportionation to form Cu0 and CuII.155 The amount of disproportionation observed is dependent upon the relative stabilities of the copper species in the reaction mixture, including the effects of any species in the mixture capable of coordinating to the copper species.155 Of the copper-based salts, CuOTf has been found to be a privileged cyclopropanation catalyst.156 This is believed to be due to the weakly coordinating nature of the triflate anion, which allows the copper carbene to coordinate to the alkene during the reaction.156

Following on from CuOTf being the most successful screened catalyst for the cyclopropanation of PVS with EDA, it was apparent that the slow addition of the diazo compound over 8 hours reduced the utility of the reaction. Evans and co-workers reported a procedure where a more dilute solution of diazo reagent was added over only 1.5 hours, which gave them good to excellent yields of cyclopropanes through the CuI-catalysed cyclopropanation of styrene.105 This more rapid diazo addition protocol was tested on the PVS cyclopropanation, with almost identical results being obtained for the 1.5-hour and 8-hour addition protocols (Table 2). The 1.5-hour diazo addition protocol was therefore carried forward due to the significant improvement in practicality. It was evident from the reaction mixture after work-up that the quantity of cyclopropane product and the remaining PVS did not account for all of the PVS that was added to the reaction mixture. This was due to polymerisation of PVS, which readily occurred at ambient temperature, resulting in insoluble polymeric material being formed during the reaction. In addition to the risk of heating diazo compounds,

keeping PVS polymerisation at a minimum was a second reason why a low reaction temperature was desirable.

Table 2: The effect of diazo compound addition time on the CuOTf-catalysed cyclopropanation

O CuOTf⋅toluene EtO O EtO O (0.5 mol%) S EtO Ph CH2Cl2, 30 °C, 24 h Ph Ph N2 S S 1.0 equiv 15 16

Entry Addition time Remaining PVS dr Yield (h) (equiv) (trans:cis) trans + cis (%) 1 8 0.32 51:49 33 2 1.5 0.37 50:50 33

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

The next variable to be optimised was the reaction solvent. A diverse range of solvents were tested, investigating the effects of solvent polarity and whether chlorinated or aromatic solvents were particularly effective (Table 3). Chlorinated solvents gave the highest yields (entries 1–3), with chloroform being optimal (entry 2). Non-chlorinated solvents gave significantly lower yields in all cases. Aromatic solvents (entries 4 and 5) favoured the formation of the trans-diastereoisomer, producing the highest diastereoselectivities observed during the solvent screen. It was, however, desired that the cyclopropanation of PVS with EDA would be non-stereoselective, so that a single cyclopropanation reaction would generate both diastereoisomers 15 and 16 in substantial quantities. This would give two stereoisomeric cyclopropyl scaffolds with significantly different synthetic vectors. Both cyclopropyl scaffolds could then be taken forward for divergent functionalisation to generate a wide range of products with a broad spectrum of functionalities and 3-dimensional structures. Therefore, due to it giving the highest yield and possessing the advantage of reasonably low diastereoselectivity, chloroform was taken forward as the reaction solvent for further optimisation.

Table 3: Solvent effects on the CuOTf-catalysed cyclopropanation of PVS with EDA

O CuOTf⋅toluene EtO O EtO O (0.5 mol%) S EtO Ph solvent, 30 °C, 24 h Ph Ph N2 S S 1.0 equiv 15 16

Entry Solvent Remaining PVS dr Yield (equiv) (trans:cis) trans + cis (%)

1 CH2Cl2 0.37 50:50 33 2 CHCl3 0.27 58:42 41 3 1,2-DCE 0.17 52:48 35 4 Toluene 0.32 65:35 12 5 Benzene 0.30 63:37 21 6 Hexane 0.54 52:48 10 7 THF 0.14 55:45 26 8 Ethyl acetate 0.19 55:45 10

1,2-DCE = 1,2-Dichloroethane. Diastereoselectivity was determined by 1H NMR spectroscopy.

At this point in the optimisation a series of control reactions were performed, to investigate how the polymerisation of PVS was affected by the presence of EDA and CuOTf (Table 4).

Table 4: Control reactions study on the CuOTf-catalysed cyclopropanation of PVS and EDA

O CuOTf⋅toluene EtO O EtO O (0.5 mol%) S EtO Ph CHCl3, 30 °C Ph Ph N2 S S 1.0 equiv 15 16

Entry Variable Reaction time Remaining PVS Remaining PVS Yield (h) (equiv) (equiv) trans + cis (%) 1 No CuOTf 24 0.88 0.87 0 2 No EDA 24 0.83 - 0 3 No CuOTf or EDA 24 0.70 - 0 4 No CuOTf or EDA 48 0.56 - 0

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene).

Without the addition of CuOTf, no cyclopropanation was observed as expected (Table 4, entry 1). A 12% loss of PVS through polymerisation was also observed. In the absence of EDA, no cyclopropanation was observed as would be expected, and a similar amount of PVS polymerisation was observed (entry 2). With the exclusion of both CuOTf and EDA, there was a slight decrease in the amount of recovered PVS

after 24 hours, which further decreased after 48 hours (entries 3 and 4). These results indicated that PVS polymerisation was not greatly accelerated by the presence of EDA or CuOTf and that the longer the reaction time, the more PVS was consumed through polymerisation.

The degree of air and moisture exclusion was next investigated by running the reaction with either a batch of CuOTf that had been stored and handled in a glovebox as per the usual experimental procedure, or by using a batch of CuOTf that had been stored in a desiccator (Table 5).

Table 5: The effect of CuOTf storage on the cyclopropanation of PVS and EDA

O CuOTf⋅toluene EtO O EtO O (0.5 mol%) S EtO Ph CHCl3, 30 °C, 24 h Ph Ph N2 S S 1.0 equiv 15 16 Entry Catalyst storage Remaining PVS Yield (equiv) trans + cis (%)

1 Glovebox 0.27 41 2 Desiccator 0.41 41 Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene).

Both batches of CuOTf gave the same yield of cyclopropanes, however the reaction that utilised catalyst from a desiccator gave 14% less recovered PVS (Table 5, entries 1 and 2). Having more PVS in the reaction mixture was beneficial to the reaction, and may have proved to be significant after further reaction optimisation, so the CuOTf used continued to be stored and handled under glovebox conditions.

During reaction optimisation it was apparent that the cyclopropanation was slightly capricious, with repeat reactions giving small variations in yield. To ensure accurate and reliable results, all reactions that investigated a particular parameter of the reaction optimisation were run simultaneously, using the same equipment and reagents. To ensure valid conclusions could be drawn from sets of data that were probing different parameters of the reaction optimisation, and so had been set up at different times, a control reaction was run alongside each batch of optimisation

reactions. The results of these control reactions were compared to each other to ensure that any differences in yields during optimisation were the result of intentional and reproducible changes to the reaction conditions as part of the optimisation process.

To check that the capricious nature of the reaction was not a result of product instability to either work-up or chromatography conditions, a stationary phase stability study was conducted, similar to that described by the Bull group.157 This study involved stirring a known amount of a 1:1 mixture of 15 and 16 in a medium of interest for 1 hour at room temperature and measuring the difference in the amount of the cyclopropanes present after this time through 1H NMR analysis with comparison to an internal standard. This study showed that the cyclopropane products were stable to the typical chromatography eluent used (n-hexane:ether mixture), silica, silica + 1% Et3N, basic ® Al2O3 and Florisil . A moderate reduction in the amount of recovered cyclopropanes had occurred over the hour with neutral Al2O3 (Grade I). This showed that the cyclopropane products were stable for prolonged periods of time under the standard work-up and chromatography conditions. Therefore, the variability in the cyclopropanation results would be monitored throughout the remaining optimisation process through control reactions.

The effect of reducing the reaction scale was investigated next. Due to the purification of PVS by vacuum distillation prior to use requiring heating to approximately 70 °C, combined with the thermally induced polymerisation of PVS observed at ambient temperatures and above, significant amounts of PVS were being consumed as a result of polymerisation-attributed losses during vacuum distillation. Reducing the reaction scale from 1.0 mmol to 0.5 mmol was investigated (Table 6, entries 1 and 4). Whilst a decrease in cyclopropanation yield and diazo dimerisation was observed, this could be attributed to the heterogeneous nature of the catalyst.

Table 6: The effect of scale and temperature on the CuOTf-catalysed cyclopropanation reaction

O CuOTf⋅toluene EtO O EtO O (0.5 mol%) S EtO Ph CHCl , temperature N 3 Ph Ph 2 24 h S S 1.0 equiv 15 16

Entry mmol of PVS Temperature EDA dimerisation dr Yield (°C) (%) (trans:cis) trans + cis (%) 1 1.0 30 30 56:44 41 2 0.5 20 13 53:47 15 3 0.5 25 6 50:50 22 4 0.5 30 5 56:44 27 5 0.5 35 6 56:44 27

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

To investigate the temperature-dependence of the reaction, experiments were run at temperatures ranging 20–35 °C (Table 6, entries 2–5). The yield of cyclopropanes increased from 20 °C until 30 °C, after which there was no improvement. To gain the maximum benefits from both reaction output and safety, a temperature of 30 °C was deemed optimum. The “EDA dimerisation %” is the percentage of reactant EDA that underwent dimerisation to form either diethyl fumarate or diethyl maleate side-products as measured by analysis of the 1H NMR spectrum for the reaction mixture. The amount of dimerisation didn’t vary significantly between 20 °C and 35 °C (entries 2–5).

The next variable to be optimised was the catalyst loading (Table 7). Increasing the catalyst loading to 1 mol% gave a significant increase in the yield of cyclopropanes, however further increasing it to 2 mol% gave no benefit. This appeared to be due to the CuOTf reaching a solubility limit in the reaction mixture, and at 2 mol% catalyst loading small particles of undissolved catalyst could be seen. From this investigation it was concluded that 1 mol% catalyst loading was optimum. Due to the acidic nature of chloroform,158 and the potential sensitivity of PVS polymerisation159 and CuOTf deactivation to acidic conditions,155 20 mol% of the sterically hindered base 2,6-lutidine was added as an additive (entry 4). This, however, decreased the yield of cyclopropanes obtained and did not reduce PVS polymerisation.

Table 7: Effect of catalyst loading on the CuOTf-catalysed cyclopropanation of PVS with EDA

O CuOTf⋅toluene EtO O EtO O (mol%) S EtO Ph CHCl , 30 ºC N 3 Ph Ph 2 24 h S S 1.0 equiv 15 16

Entry Catalyst loading EDA dimerisation dr Yield (mol%) (%) (trans:cis) trans + cis (%) 1 0.5 5 56:44 27 2 1.0 20 56:44 45 3 2.0 13 57:43 40 4 1.0a 20 57:43 28

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy. a + 20 mol% 2,6-lutidine.

To investigate how the reaction progressed with time, the cyclopropanation was stopped after 3, 18 and 24 hours and the three results compared (Table 8). The reaction proceeded rapidly at first but slowed down significantly after the first 3 hours (entry 1). The difference between the yields at 18 hours and 24 hours was only 4%, however it showed that the reaction was still proceeding (entries 2 and 3). The reaction time was therefore kept at 24 hours.

Table 8: The effect of reaction time on the CuOTf-catalysed cyclopropanation of PVS with EDA

O CuOTf⋅toluene EtO O EtO O (1 mol%) S EtO Ph CHCl , 30 ºC N 3 Ph Ph 2 Time S S 1.0 equiv 15 16

Entry Time dr Yield (h) (trans:cis) trans + cis (%)

1 3 53:47 30 2 18 53:47 40 3 24 57:43 44

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

The next parameters to be investigated were the number of equivalents of diazo reagent used and the diazo reagent itself (Table 9). Due to copper-catalysed diazo dimerisation reducing the amount of diazo reagent in the reaction mixture, it seemed

plausible that increasing the equivalents of the diazo compound could be a way to increase the yield of the cyclopropanation reaction. This however was not the case and the reaction appeared to be insensitive to the number of equivalents of diazo compound for the range observed (entries 1–3). For the remaining optimisation with EDA, 2.0 equivalents of EDA were used due to the possibility that an increased amount of EDA may improve the reaction with further-optimised conditions.

Table 9: The effect of diazo equivalents on the CuOTf-catalysed cyclopropanation of PVS with EDA

O CuOTf⋅toluene RO O RO O (1 mol%) S RO Ph CHCl3, 30 ºC, 24 h Ph Ph N2 S S

Entry R Diazo compound Diazo dimerisation dr Yield equivalents (%) (trans:cis) trans + cis (%) 1 Et 1.0 18 56:44 45 2 Et 1.5 12 56:44 45 3 Et 2.0 11 54:46 46 4 t-Bu 1.0 11 60:40 25

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

To probe the steric effects of the diazo compound in the cyclopropanation, tert-butyl diazoacetate was tested, with a significant decrease in yield observed (entry 4). There was very little change in the diastereoselectivity of the reaction, and the trans-diastereoisomer was still favoured. At this point in the optimisation almost all reaction parameters had been assessed and the yield of cyclopropanes had plateaued at around 45%.

The incorporation of a ligand can enable the reactivity of the catalytic metal centre to be tuned. The addition of a ligand can also improve solubility in organic solvents as well as provide a scaffold from which asymmetric induction can be explored. In particular, bisoxazoline-derived (BOX) ligands have shown significant success in copper-catalysed cyclopropanation reactions. Due to its frequent appearance in the literature and its availability, ligand 17 was utilised for further optimisation. Once the reaction conditions had been further optimised for the inclusion of 17, alternative

ligands would also be analysed. Due to the BOX ligand being highly enantioenriched, chiral induction to produce enantioenriched cyclopropane products was feasible. Any enantioenrichment observed in the product cyclopropanes will not be extensively analysed in this section. Such observations will be discussed in Section 2.1.4.1 as a part of the development of an asymmetric transition metal-catalysed cyclopropanation of PVS with EDA.

Before ligand 17 was tested in the cyclopropanation of PVS with EDA, it was important to conduct a test to ensure that the CuI(BOX) complex was being formed and utilised successfully. The cyclopropanation of styrene with EDA was therefore performed, and the results compared to the same reaction reported by Evans and co-workers (Scheme 22).105 The hypothesis was that if the results were similar then it would suggest that the CuI(BOX) complex was indeed being formed successfully. The method to form the complex involved the CuOTf and ligand being stirred in chloroform for 1 hour at room temperature. The reaction mixture was then warmed to 30 °C, styrene added, followed by the slow addition of a solution of EDA in CHCl3 via syringe pump over 1.5 hours. After the slow addition was complete the reaction mixture was stirred for a further 14 hours.

O O N N

17 (1.1 mol%)

O CuOTf⋅toluene EtO O EtO O (1 mol%) EtO Ph CHCl3, 30 ºC, 16.5 h N2 Ph Ph 2.0 equiv 0.5 mmol 18 19

This work Evans and co-workers 94% yield No yield declared trans:cis = 68:32 trans:cis = 68:32 ee (trans) = 66% ee (trans) = 49%

Scheme 22: CuI(BOX)-catalysed cyclopropanation of styrene with EDA. Yield determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

An excellent yield of 94% was achieved, with the same diastereoselectivity as that observed by Evans and co-workers.105 In addition, the enantioenrichment of the trans-diastereoisomer was found to be greater than that previously recorded.105

The results from this test showed that the method used to generate and use the CuI(BOX) complex was successful, and so this protocol was applied to the cyclopropanation of PVS with EDA (Table 10). When enantioenriched BOX ligand 17 was incorporated into the CuOTf-catalysed system, the yield of cyclopropane products improved to 54% (Table 10, entry 1), which was a significant improvement on the 46% obtained without the addition of BOX 17 (Table 9, entry 3). The asterisk of products 15* and 16* denotes enantioenriched material, in this instance from the asymmetric cyclopropanation. After this the CuI source was evaluated. Whilst CuOTf had proved hugely successful in copper-catalysed cyclopropanation reactions, a variety of other CuI sources were tested for an improvement on the current system. Copper(I) halides were unsuccessful at the cyclopropanation (Table 10, entries 2–4), either giving very low yields on no cyclopropane products at all. Whilst Cu(MeCN)4BF4 gave a significantly lower yield than CuOTf, it did catalyse the cyclopropanation reaction reasonably well. From these results it appeared that CuI sources with weakly coordinating anions performed best in this cyclopropanation, which matched observations by Salomon and Kochi on a variety of CuI-catalysed cyclopropanation reactions.156 This was explained to be a result of CuI sources with weakly coordinating counterions being able to coordinate the reactant alkene during the reaction.156

Table 10: The effect of CuI source on the catalysed cyclopropanation of PVS with EDA

O O N N

17 (1.1 mol%) O EtO O EtO O CuI source (1 mol%) S EtO Ph CHCl3, 30 ºC, 24 h Ph Ph N2 S S 2.0 equiv 15* 16*

Entry Catalyst Remaining PVS Diazo dimerisation dr Yield (equiv) (%) (trans:cis) trans + cis (%) 1 CuOTf·toluene 0.00 25 50:50 54 2 CuCl 0.00 3 50:50 4 3 CuBr 0.29 48 - 0 4 CuI 0.08 18 38:62 8 5 Cu(MeCN)4BF4 0.02 10 50:50 36

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

With this counterion effect in mind, additives were tested which could act as a source of an alternative weakly coordinating anion (Table 11).

Table 11: The effect of additives on the CuI-catalysed cyclopropanation of PVS with EDA

O O N N

17 (1.1 mol%)

O CuOTf⋅toluene (1.0 mol%) EtO O EtO O Additive (2.0 mol%) S EtO Ph CHCl3, 30 ºC, 24 h Ph Ph N2 S S 2.0 equiv 15* 16*

Entry Additive Remaining PVS Diazo dimerisation dr Yield (equiv) (%) (trans:cis) trans + cis (%) 1 None 0.00 25 50:50 54 2 AgSbF6 0.07 30 52:48 56 3 AgPF6 0.01 14 53:47 47

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

The addition of silver(I) salts with hexafluoroantimonate and hexafluorophosphate anions did not provide significant improvements to the cyclopropanation reaction, so were not investigated further (Table 11).

The next parameter to be optimised was the method of solvent purification. Chloroform had been identified as the optimal solvent early in the optimisation (Table 3, entry 2). Up until this point the chloroform had been distilled immediately prior to use by stirring the chloroform with Na2CO3 for 10 minutes (pre-dry) before being distilled over

Na2SO4. However, slight variations in yields were being observed and as a result, control reactions had been run alongside each set of reactions to ensure valid and comparable results were obtained. It was a possibility that small differences in the chloroform purity were generating the observed slight variations in the cyclopropanation results, and that a more robust purification may resolve this. To this end, the pre-dry method, distillation drying agent and a filtration procedure were analysed, to investigate whether a particular set-up removed impurities more effectively than the others. Firstly, the commercial chloroform was tested without purification, which gave a 35% yield (Table 12, entry 1). This was a significant decrease from the 54% obtained previously (Table 11, entry 1), showing that the water content of the solvent was an important factor for the reaction. Next, filtration of the solvent through a pad of a drying agent and basic acid scavenger was investigated

(entries 2–4). No benefit was observed from K2CO3 or neutral alumina (Grade I), and a significant yield decrease was observed with basic alumina (Grade I). Next the pre-dry and distillation procedures were assessed (entries 5–7). The optimum procedure from those tested was our initial procedure; pre-dry with Na2CO3 followed by distillation over Na2SO4 (entry 7). The 47% yield obtained illustrated the characteristic variability of this reaction (compare to 54%, Table 11, entry 1), hence investigation into solvent purification continued. The next stage was to combine the optimal pre-dry and distillation procedure with a filtration step (entries 8–10), however these efforts made no constructive difference to the reaction. Using chloroform that had been distilled and then stored in a round bottomed flask under an inert atmosphere for 24 hours resulted in a significant decrease in yield (entry 11), which demonstrated the necessity for freshly dried solvent.

Table 12: Solvent, reagent and work-up effects on the cyclopropanation of PVS with EDA

O O N N

17 (1.1 mol%) O EtO O EtO O CuOTf⋅toluene (1.0 mol%) S EtO Ph CHCl3, 30 ºC, 24 h Ph Ph N2 S S 2.0 equiv 15* 16* Entry Pre-dry Distillation Filtration Work-up Remaining Diazo Yield PVS dimerisation trans + cis (equiv) (%) (%) 1 - - - Silica 0.01 13 35 2 - - K2CO3 Silica 0.18 12 35 3 - - Neutral Al2O3 Silica 0.15 20 31 4 - - Basic Al2O3 Silica 0.25 14 27 5 K2CO3 Na2SO4 - Silica 0.07 15 41 6 CaCl2 CaCl2 - Silica 0.08 17 36 7 Na2CO3 Na2SO4 - Silica 0.06 12 47 8 Na2CO3 Na2SO4 K2CO3 Silica 0.09 16 41 9 Na2CO3 Na2SO4 Neutral Al2O3 Silica 0.12 18 48 10 Na2CO3 Na2SO4 Basic Al2O3 Silica 0.37 17 32 a 11 Na2CO3 Na2SO4 Basic Al2O3 Silica 0.11 23 23 ® 12 Na2CO3 Na2SO4 Basic Al2O3 Celite 0.17 19 34 13 Na2CO3 Na2SO4 Basic Al2O3 EDTA 0.08 15 35 b ® 14 Na2CO3 Na2SO4 Basic Al2O3 Celite 0.20 23 35 c 15 Na2CO3 Na2SO4 - Silica 0.02 4 44 c 16 Na2CO3 Na2SO4 Neutral Al2O3 Silica 0.11 20 47 c ® 17 Na2CO3 Na2SO4 Basic Al2O3 Celite 0.00 4 43 d ® 18 Na2CO3 Na2SO4 - Celite 0.00 27 50

Yields determined by 1H NMR spectroscopy with comparison to internal standard a b (1,3,5-trimethoxybenzene or dibenzyl ether). CHCl3 aged for 1 day. PVS not vacuum distilled prior to use. c 2 mol% of catalyst, 2.2 mol% of ligand. d 5 mol% of catalyst, 5.5 mol% of ligand.

With no improvement in yield obtained from the investigation into solvent purification, the optimisation proceeded to testing various reaction work-up conditions and other variables. The work-up for the reaction up until this point had been filtration through a pad of silica. A variation using a pad of Celite® (entry 12) gave comparable results to a silica work-up (entry 10). A work-up that consisted of adding EDTA to sequester the copper followed by an aqueous work-up also gave comparable yields (entry 13). Using PVS that had not been purified by vacuum distillation prior to use did not reduce the yield of cyclopropanes (entry 14). Increasing the catalyst loading to 2 mol% and the ligand loading to 2.2 mol% (entries 15–17) increased the yield of cyclopropanes significantly, with the larger effect observed with the optimised pre-dry and distillation,

followed by either no filtration step (entry 15) or filtration with neutral alumina (entry 16). Increasing the catalyst loading to 5 mol% and the ligand loading to 5.5 mol% increased the yield slightly, reaching 50% (entry 18). At a catalyst loading of 5 mol% the copper complex was not fully dissolved in the reaction, with solid material being visible in the reaction mixture, which explained why such a small increase in yield was observed upon proceeding from a catalyst loading of 2 mol% up to 5 mol%.

A lot of work had been carried out towards the optimisation of a CuI-catalysed cyclopropanation of PVS with EDA, with moderate yields being achieved. To improve the yield, a different system was considered. Given the wealth of reports of CuI-catalysed cyclopropanations of styrenes, the application of the developed conditions to a phenylsulfide-substituted styrene was investigated. This offered the possibility of increased yields compared to the cyclopropanation using PVS due to the more electron-rich alkene, whilst still retaining the desired phenyl sulfide functional handle for use during later scaffold derivatisation. The synthesis of cis-substituted styrene 20 proceeded from thiophenol and phenylacetylene, producing only the cis-diastereoisomer (Scheme 23) using a procedure from Deng and co-workers.160 Using the developed CuI-catalysed cyclopropanation conditions on vinyl sulfide 20, no cyclopropane-containing products were obtained (Scheme 24).

K3PO4 (1.5 equiv) SH N-Methyl-2-pyrrolidone S 80 °C, 24 h (1.5 equiv) 20 71% Scheme 23: Synthesis of a phenylsulfide-substituted styrene

O O N N

17 (1.1 mol%) O EtO O EtO O Ph CuOTf⋅toluene (1.0 mol%) EtO S Ph CHCl3, 30 ºC, 24 h Ph Ph N2 Ph S Ph S 2.0 equiv 21* 22* Scheme 24: Attempted CuI-catalysed cyclopropanation of a cis-substituted vinyl sulfide

With a large number of parameters explored, the optimisation of the CuI-catalysed cyclopropanation of PVS with EDA had been thoroughly investigated. However, the reaction gave only moderate yields of the desired cyclopropanes, utilised a catalyst that necessitated storage and handling in a glovebox, and required a slow-addition protocol for addition of the diazo reagent.

Attention therefore returned to other potential transition metal catalysts that may be suitable for the cyclopropanation of PVS with EDA. Of particular interest was CoII, which had received significant recent attention for the cyclopropanation of non-styrene-based alkenes.139

2.1.3. CoII-Catalysed Cyclopropanation of PVS with EDA Cobalt complexes have been shown to be very effective at catalysing the cyclopropanation of non-electron-rich alkenes.130,161,162 The use of novel CoII complexes has greatly facilitated the cyclopropanation of non-styrene-based derivatives, with styrenes occupying a huge proportion of the transition metal-catalysed cyclopropanation literature owing to their electron-rich nature.163,164

In particular, White and Shaw reported utilising a CoII(salen)-type complex (23, Scheme 25) to perform asymmetric cyclopropanation on a variety of 1,1-substituted alkenes producing a range of tri-substituted cyclopropanes.139 Within the scope there was a single example using a 1,1-substituted vinyl sulfide (Scheme 25). The synthesis produced the tri-substituted cyclopropanes in excellent yields and with high diastereo- and enantioselectivities, however for the vinyl sulfide example there was a significant reduction in all three outputs compared to the rest of the scope. An issue with this methodology is the extensive catalyst synthetic route (11 steps) which resulted in only a 12% overall yield.165 With such a lengthy catalyst synthesis it would require a considerable amount of time and resources before even beginning the synthesis of the desired cyclopropane-containing compounds. This publication does however demonstrate how CoII(salen)-type complexes can be used to great effect to induce considerable enantioenrichment in a vinyl sulfide substrate, which due to its

conformational flexibility is a much more challenging substrate than more rigid examples such as styrene derivatives.

N N Co O t-Bu t-Bu O t-Bu t-Bu 23

(5.0 mol%) EtO O O EtO O S KSAc (5.0 mol%) Ph EtO n-Pr S n-Pr CH2Cl2, rt, 48 h N2 Ph S Ph n-Pr (1.5 equiv) 24 25 24:25 = 16:1 87% yield (24 + 25) 88% ee Scheme 25: Asymmetric CoII-catalysed cyclopropanation of a 1,1-substituted vinyl sulfide139

With CoII having been shown to be capable of catalysing cyclopropanation reactions effectively,130,139,161-164 the development of a CoII-catalysed cyclopropanation of PVS with EDA was therefore explored.

A concise account of this work can be found in the European Journal of Organic Chemistry (see Appendix 1).166

2.1.3.1. CoII-Catalysed Cyclopropanation Optimisation Initially, the conditions by White and Shaw served as a starting point for a CoII-catalysed cyclopropanation of PVS with EDA.139 In contrast to the catalyst designed by White and Shaw (Scheme 25),165 this methodology would ideally utilise a readily accessible catalyst. A CoII(salen)-type complex was chosen that was based on the Jacobsen ligand,167 a ligand that has been very successful in a variety of transition metal-catalysed reactions including cyclopropanations and epoxidations (Scheme 26).110,168 This CoII complex was commercially available169 and could be synthesised in two steps on multi-gram scale (Scheme 26). The synthesis comprised of diimine formation followed by CoII complexation to give the desired CoII(salen)-type

complex. Due to the commercial availability of highly enantioenriched trans-1,2-diaminocyclohexane the enantioenriched CoII complex could also easily be synthesised.

H2N NH2 O EtOH, reflux, 2 h 81% N N t-Bu OH Co 2) Co(OAc) 2 t-Bu O O t-Bu t-Bu (1.0 equiv) (2.0 equiv) EtOH, reflux, 4 h t-Bu t-Bu 91% 26 28 Scheme 26: Synthesis of racemic complex 28 via Schiff base 27 for use in this work

White and Shaw observed that the CoII-catalysed cyclopropanation of 1,1-disubstituted alkenes was promoted by electron-donor additives.139 Of these additives, potassium thioacetate was found to be particularly efficient. The rationale for this behaviour was that the additive bound to one axial site of the cobalt (salen)-type complex, activating the complex towards reaction with the diazo reagent.139

Beginning the optimisation process towards an effective CoII-catalysed cyclopropanation of PVS with EDA, catalyst 28 (5 mol%) with potassium acetate

(5 mol%) were used in CH2Cl2 (0.2 M) at room temperature (22 °C) (Table 13, entry 1). No reaction was observed at room temperature so warmer temperatures were tested (entries 2 and 3). At 30 °C only a reduction in PVS recovery was observed as a result of thermal polymerisation, with the polymeric material visible in the flask (entry 2). At 40 °C however, a 22% yield of cyclopropanes 15 and 16 was observed in an approximately 1:1 ratio of diastereoisomers as determined through analysis of the 1H NMR spectrum of the reaction mixture following aqueous work-up (entry 3). Notably no dimerisation of the diazo reagent was observed, with no diethyl maleate or diethyl fumarate side-products present in the 1H NMR spectrum of the reaction mixture prior to purification. This behaviour is typical for cobalt-catalysed cyclopropanation reactions utilising diazo reagents.170 This meant that there was no requirement to use

a slow addition protocol for the diazo compound. This also allowed the diazo reagent to be used as the limiting reagent instead of in excess; a desirable situation due to the potentially explosive nature of diazo compounds. Additionally, CoII catalyst 28 was air and moisture stable so it did not need to be stored and handled in a glovebox, further increasing the practicality of this reaction. Running the reaction without the potassium thioacetate additive significantly increased the yield of cyclopropanes, suggesting that the additive was inhibiting the cyclopropanation (entry 4).

Table 13: Effect of temperature and KSAc additive on the CoII-catalysed cyclopropanation of PVS with EDA

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 (5.0 mol%) O EtO O EtO O Additive (5.0 mol%) S EtO Ph CH2Cl2 (0.2 M), Temperature, 24 h Ph Ph N2 S S 0.3 mmol (1.5 equiv) 15 16

Entry Additive Temperature Remaining PVS dr Yield (°C) (equiv) (trans:cis) trans + cis (%) 1 KSAc 22 1.00 - - 2 KSAc 30 0.85 - - 3 KSAc 40 0.07 47:53 22 4 - 40 0.09 52:48 40

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

With the knowledge that CoII(salen)-type complex 28 successfully catalysed the desired reaction, a solvent screen was undertaken. A broad range of solvents were investigated (Table 14). Chlorinated solvents such as 1,2-dichloroethane, 1,2-dichlorobenzene and chlorobenzene gave similar yields to dichloromethane, however chloroform was notably inferior and carbon tetrachloride gave no cyclopropanation (entries 1–6). Aromatic solvents performed well (entries 6–9), with benzene giving a 73% yield (entry 8). Hydrocarbon solvents resulted in reasonable yields, with the reaction in cyclohexane producing a 55% yield of cyclopropanes

(entries 10–12). More polar organic solvents gave a range of successes (entries

13–16), with tert-butyl methyl ether giving a good yield of 69% (entry 15). Finally, H2O was tested which gave a quantitative yield of cyclopropanes (entry 17). The reagents were not soluble in H2O, and the reaction mixture appeared as regions of organic-soluble species being agitated by the stirring H2O. Following on from this observation the reaction was run as a stirring mixture of neat reagents which produced a 93% yield of cyclopropanes (entry 18). It therefore appeared that a high concentration of reagents was advantageous to the reaction. Interestingly, all solvents explored gave a dr of approximately 50:50.

Table 14: Effect of solvent on the CoII-catalysed cyclopropanation of PVS with EDA

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O EtO O EtO O (5.0 mol%) S EtO Ph Solvent (0.2 M), 40 °C, 24 h Ph Ph N2 S S 0.3 mmol (1.5 equiv) 15 16

Entry Solvent Remaining PVS dr Yield (equiv) (trans:cis) trans + cis (%)

1 CH2Cl2 0.09 52:48 40 2 CHCl3 0.58 48:52 13 3 1,2-DCE 0.17 47:53 41 4 1,2-DCB 0.62 50:50 38 5 CCl4 0.74 - 0 6 PhCl 0.50 50:50 50 7 Toluene 0.20 45:55 53 8 Benzene 0.23 48:52 73 9 Xylenes 0.33 49:51 41 10 Pentane 0.08 50:50 34 11 Cyclohexane 0.80 45:55 55 12 Heptane 1.02 48:52 29 13 THF 0.04 45:55 14 14 Ethyl acetate 0.72 51:49 36 15 TBME 0.54 48:52 69 16 i-PrOH 0.53 51:49 44 17 H2O 0.41 47:53 100 18 No solvent 0.00 46:54 93

Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

The solvent screen had shown that conducting the cyclopropanation on H2O (Table 14, entry 17) or neat (Table 14, entry 18) produced excellent yields of the desired bifunctional cyclopropyl-scaffolds on a 0.3 mmol scale. The aim of the overall approach was to be able to use these bifunctional scaffolds in a plethora of reactions, and so large quantities of the scaffolds would be required, ideally from a single reaction. Therefore, the next step was to investigate the scalability of the cyclopropanation reaction in both systems.

To do this, the scale of the reaction was gradually increased from 0.3 mmol. Initially, the number of equivalents of PVS was decreased as the reaction scale increased, reducing the excess from 0.5 to 0.1 equivalents (Table 15, entries 1–6). This was due to the possibility that the thermal polymerisation of PVS may remain reasonably consistent throughout cyclopropanations of varying scales. This however was observed not to be the case, and a decrease in yield was observed both neat

(entries 1, 3, 5) and on H2O (entries 2, 4, 6). Despite this, the cyclopropanation gave good results both neat and on H2O up to a scale of 10 mmol. When the reaction was run neat on a 20 mmol scale a significant exotherm was generated with concomitant gas evolution observed, also producing a significantly lower yield of cyclopropanes (entry 9). This exotherm and rapid gas evolution was not observed when the 20 mmol reaction was carried out on H2O, and an excellent yield was achieved (entry 10). This is unsurprising as H2O is an excellent heat sink because of its large heat capacity, facilitating exotherm dissipation.171 Due to the significantly increased safety and yield of the 20 mmol scale cyclopropanation reaction when run on H2O compared to when run neat, further scale increases for the neat protocol was not investigated further.

Increasing the reaction scale further on H2O using 40 mmol of diazo compound produced an excellent yield with no vigorous gas evolution (entry 11). This 40 mmol reaction produced 7.9 g of isolated cyclopropanes.

Table 15: The effect of reaction scale on the cyclopropanation of PVS with EDA either neat or on H2O

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O EtO O EtO O (5.0 mol%) S EtO Ph H2O (0.2 M) or neat, 40 ºC, 24 h Ph Ph N2 S S 0.3 mmol 15 16

Entry mmol of EDA Solvent Reactant PVS dr Yield (equiv) (trans:cis) trans + cis (%)

1a 0.3 Neat 1.5 46:54 93 a 2 0.3 H2O 1.5 47:53 100 3b 2.7 Neat 1.2 45:55 86 4 2.7 H2O 1.2 47:53 100 5 5.0 Neat 1.1 47:53 60 c 6 5.0 H2O 1.1 47:53 81 7 10 Neat 1.5 53:47 70 c 8 10 H2O 1.5 47:53 85 9 20 Neat 1.5 52:48 46 c 10 20 H2O 1.5 45:55 85 c 11 40 H2O 1.5 46:54 89 a Yield determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). 1 b c Diastereoselectivity was determined by H NMR spectroscopy. Reaction was run at 30 °C. H2O (0.5 M).

The optimised conditions (Table 15, entry 11) fulfilled the aims for the cyclopropanation reaction by allowing access to the desired bifunctional cyclopropanes through a high yielding, scalable and practical CoII-catalysed cyclopropanation of PVS with EDA.

2.1.3.2. Purification of Large-Scale Cyclopropanation Reactions When the 28-catalysed cyclopropanation between PVS and EDA was carried out on a 10 mmol scale or larger, a small amount of an impurity was present that discoloured the cyclopropane products from pale yellow to dark brown. The impurity could not be removed from the cyclopropane products effectively through standard silica chromatography, nor could it be obtained cleanly to aid its identification. However, a small sample of the impurity mixed with the CoII(salen)-type catalyst 28 was obtained through careful chromatography of a cyclopropanation reaction mixture, giving a red/brown solid. The 1H NMR spectrum of the sample possessed very broad peaks,

indicating that the sample contained paramagnetic species, however this could be due to either the impurity being paramagnetic and/or the paramagnetic CoII(salen)-type catalyst 28 present in the mixture (Figure 24). IR spectroscopy did not reveal the presence or absence of significant peaks compared to that of a sample of pure CoII(salen)-type catalyst 28, indicating that the unknown species possessed a similar structure to 28. The addition of certain solvents (e.g. i-hexane) to a sample of CoII(salen)-type catalyst 28 resulted in very rapid formation of a brown solid material that strongly resembled the impurity obtained from the CoII-catalysed cyclopropanation.

Figure 24: The 1H NMR spectrum for a mixture of the unknown impurity and CoII(salen)-type complex 28

Analysis of CoII(salen)-catalysed processes showed that a possible side-reaction was the oxygenation of the CoII(salen)-type complex to form oxidised cobalt species (Figure 25).172,173,174,175 With notable separate examples from Mingos176 and from Jackson and co-workers,177 the oxygenation of CoII amine and Schiff base complexes most commonly form characteristically brown µ-peroxo-dimeric species (Figure 25A). These dinuclear species are diamagnetic, with both cobalt ions in their +3 oxidation state. The structure of these species has been confirmed by characterisation including X-ray crystallography.178,179

Less frequently, paramagnetic mononuclear ‘superoxo-like’ species are formed, usually when the cobalt complex is particularly sterically bulky, hindering the formation of a µ-peroxo-dimeric species (Figure 25B). Characterisation including EPR

spectroscopy and X-ray crystallography have confirmed both the electronic and 1 geometric structure of these species, possessing an O2 with an end-on (h ) binding mode, a terminal oxygen radical and the cobalt in the +3 oxidation state.180,181,182,183

A mononuclear ‘sideways bonded’ h2-superoxo complex is also possible with certain ligands, producing a diamagnetic complex, though their existence is rare (Figure 25C).177 The structure of such a species possessing a tetraamine ligand has been confirmed by X-ray crystallography.177

N N Co O O O O O O O O N N N N N N Co Co Co O O O O N N A B C Figure 25: The various types of cobalt-based molecular oxygen adducts

Through the observations made and the existing literature on the matter, the impurity was assigned as an oxygenated Co(salen)-type species, however to determine which mode of O2 binding was present would require the isolation of the species. Both the diamagnetic µ-peroxo-bridged dimer and the paramagnetic ‘superoxo-like’ species formed from catalyst 28 have been reported and characterised by UV–vis and electron paramagnetic resonance (EPR) NMR spectroscopy by the Doorslaer group.178 The impurity posed a problem, as it couldn’t be readily removed from the desired cyclopropane products.

In order to use the CoII-catalysed cyclopropanation on large scales in an effective manner, a protocol was required that would allow the easy removal of this impurity, granting access to the pure cyclopropane products. In developing a successful purification method, it was hoped to also gain knowledge on why purification of the cyclopropanation reaction mixture became an issue with larger reaction scales.

The first purification method to be investigated was the separation of the cyclopropanes and the Co salen-derived impurity between non-polar and polar

phases. The cyclopropanes possess a non-polar nature and would therefore reside within a non-polar phase, and it was hoped that the presence of the metal in the impurity would allow for polar interactions which could draw it into the polar phase (Table 16).

Table 16: Solvent combinations tested towards cyclopropane purification

Non-polar phase Polar phase

i-Hexane H2O i-Hexane H O + MeOH N 2 BF i-Hexane 29 4 N i-Hexane DMSO i-Hexane DMSO + H2O i-Hexane DMF i-Hexane NH3(aq) (38%) 29 Xylenes DMF Xylenes DMSO

A variety of separations between i-hexane and polar solvents were attempted however none of them separated the Co(O2)(salen)-type species from the product cyclopropanes. Polar solvents were chosen that may coordinate to the metal of the impurity species and promote it entering the more polar phase. These solvents included H2O, MeOH and ionic liquid 29 (1-butyl-3-methylimidazolium tetrafluoroborate). Similarly, separation between xylenes and either DMF or DMSO did not produce the desired separation. An extension of this approach was the addition of a ligand which possessed the ability to form hydrogen bonds with suitable solvents. The hypothesis was that ligands 30–33 may coordinate to the metal of Co(salen)-type species and facilitate dissolution of the complex in aqueous media by hydrogen bonding with H2O, allowing separation from the cyclopropane products through organic extractions (Figure 26). Ligands 30–33 (5.0 equiv, with respect to 28) were added to samples of catalyst 28 in H2O (20 mL) and i-hexane (10 mL) and the resulting mixture was stirred at room temperature for 1 hour. The phases were then separated and analysed by LCMS for the presence of Co complex. For all of ligands 30–33 the Co complex remained almost exclusively present in the organic phase, so the process was repeated using Et2O (10 mL) as the organic phase. Again, the Co complex was almost entirely located in the organic phase after the addition of ligands 30–33.

N O OH P N N O P OH P K O O K HO NH2 O S S O O O O 30 31 32 33 Figure 26: Ligands tested to achieve separation between the Co-containing impurity and product cyclopropanes

The next purification approach was to investigate whether the Co(O2)(salen)-type species was insoluble enough in a non-polar solvent to precipitate out of solution, allowing its removal through filtration. i-Hexane and toluene were tested however neither proved successful. These solvents were tested again however this time with prior incubation with one of ligands 30–33 (5.0 equiv) for one hour before filtration. No precipitation was visually observed and there was no separation of materials after filtration of the solution.

The next approach was filtration through a stationary phase that would retain basic species. SCX columns are cartridges filled with a silica-based stationary phase with a benzene sulfonic acid sorbent which can be used to remove basic materials from a mixture. The aim was to investigate whether the imine nitrogen atoms in the

Co(O2)(salen)-type impurity may result in its retention, allowing the cyclopropane products to pass through unhindered. The retained species may then be obtained by eluting with NH3/MeOH. This however was not the case, and all species eluted from the SCX column in the initial methanol extraction.

Acid-catalysed hydrolysis of the Co(O2)(salen)-type species was explored as a route to decompose the impurity and allow the components to be separated from the product cyclopropanes. Immediately after a cyclopropanation reaction, 100 equivalents (with respect to 28) of HCl(aq) and methanol (10 mL) were added. The methanol was added to aid the solubilisation of the complex. The mixture was stirred in an ice bath for 1 hour, however, after extraction with i-hexane the intact impurity was still present with the cyclopropanes.

Due to the significant size difference between the product cyclopropanes and a

Co(O2)(salen)-type complex, filtration through a size exclusion medium (i.e. nanofiltration) was an option. Nanofiltration is the filtration of a solution or mixture through a membrane that possesses pores of a nanometre size. A variety of membranes possessing different pore sizes can be purchased, designed for the separation of different sized species for a variety of applications such as water treatment and food production.184 Assuming an approximately spherical molecular shape, each filter can be given an approximate molecular weight cut-off, where compounds whose MW exceeds this will be unable to pass through the filter. The MW II of the Co(O2)(salen)-type impurity was estimated to be > 600 Da, given that the Co catalyst possessed a MW of 604 Da. The MW of the diastereoisomeric cyclopropanes were 222 Da, meaning a variety of filters possessed cut-off ranges between the two

MW’s. The Dow N270 (MW cut-off 200–400 Da), GE Osmonics HL (MW cut-off

150–300 Da), TriSep TS40 (MW cut-off 200–300 Da) and Synder NFW (MW cut-off 300–500 Da) membranes were tested. The membranes spanned a range of brands to examine their individual technologies, however they all suffered from a common weakness frequently encountered in nanofiltration filter membranes which was that they were only usable in highly polar solvents; non-polar solvents resulted in their decomposition. Water was the preferred nanofiltration solvent for filter stability, however the cyclopropanation reaction mixture was insoluble in it. Therefore methanol, which was also a recommended solvent, was used for the nanofiltration procedures. Initially the nanofiltration appeared to give purified cyclopropane products, indicated by the very pale yellow filtrate. However, before the filtration was complete there was decomposition of the filter membrane in all cases, allowing all materials to pass through. This likely resulted from the build-up of lipophilic Co(O2)(salen)-type material on the filter during the filtration process, causing the filter membrane to decompose in the non-polar environment. Nanofiltration options that displayed significantly higher tolerances to non-polar solvents were available from Evonik in the form of DuraMem and PuraMem, however both were prohibitively expensive.

The next approach investigated the effect of basic additives in silica chromatography. Whilst many eluent systems had been tested early on in the purification attempts, the

effect of basic additives had not been explored. In order to do this, the reaction mixture of a 28-catalysed cyclopropanation reaction between PVS and EDA was purified by silica chromatography using an eluent of heptane + 1% Et3N. This obtained, in order of elution and after concentration under reduced pressure, the trans-cyclopropane (Rf = 0.46) as a pale yellow oil, the cis-cyclopropane (Rf = 0.30) as II a pale yellow oil, the starting Co -catalyst (Rf = 0.28) as a red solid, and when the eluent polarity was increased by eluting with 50–100% Et2O in heptane + 1% Et3N, the Co(O2)(salen)-type species (Rf = 0.00) as a brown solid (Rf values were calculated using the same eluent of 9:2 n-hexane:Et2O + 1% Et3N).

With the isolation of the Co(O2)(salen)-type species, studies into its identity were continued. The isolated sample displayed a complex 1H NMR spectrum consisting of a multitude of sharp peaks that were located at similar chemical shifts to the CoII(salen)-type complex and the salen-type ligand. The signals were not broad, implying that the sample was a diamagnetic species. The sample also produced a similar IR spectrum to the CoII(salen)-type complex and the salen-type ligand. MALDI ToF mass spectrometry analysis of the sample showed a peak corresponding to a mass of 1241.9 Da, comparable to the calculated MW of the µ-peroxo-bridged dimer, 1239.5 Da. In addition, the substance possessed the characteristic appearance common to µ-peroxo-bridged dimeric species derived from structurally similar CoII 172,173,175,177,178,179 complexes. The Co(O2)(salen)-type species was therefore assigned as the diamagnetic µ-peroxo-bridged dimer 34 (Figure 27), originating from CoII complex 28. This allowed speculation on the reason for why the impurity was generally observed on larger-scale reactions (greater than around 2.7 mmol) and not on small-scale ones (up to around 2.7 mmol). As the scale of the reaction was increased, so was both the size of the reaction vessel and the number of empty, Ar(g) flushed balloons to accommodate the increased N2(g) evolution. Whilst the reaction vessel was flushed with Ar(g) before use, any O2(g) still present in the vessel headspace or in the balloons would be capable of generating the µ-peroxo-bridged dimer of CoII complex 28. In addition, one molecule of O2 oxygenated two complexes of 28, meaning only trace quantities of O2 were required to cause perceptible levels of catalyst oxygenation.

N N Co t-Bu O O t-Bu

t-Bu O t-Bu

t-Bu O O t-Bu Co N N

Figure 27: The structure for µ-peroxo-bridged dimer 34

The addition of Et3N to the chromatography eluent had allowed separation of the Co(salen)-type species from the cyclopropanation reaction mixture. This enabled assignment of the Co(salen)-type impurity to be made, however the purification required careful chromatography to obtain the cyclopropyl scaffolds pure due to the similar Rf’s of the cis-cyclopropyl scaffold and 28. This made the basic chromatography method impractical. During chromatography with Et3N as an additive, the Co(peroxo)(salen)-type species 34 had a much lower Rf than the cyclopropanes and 28, whereas previously co-elution issues had been encountered. During chromatography, the Co(peroxo)(salen)-type species 34 appeared as a brown band, 28 as a red band and the cyclopropanes as pale yellow bands on the silica. Visually analysing the chromatographic progression of the Co-catalysed cyclopropanation reaction mixture both with and without 1% Et3N additive to the eluent revealed that in the absence of Et3N, the Co(peroxo)(salen)-type species 34 was being dragged down the column by 28 which, in turn was co-eluting with the cyclopropane products. Thus, it appeared that converting any remaining 28 in the cyclopropanation reaction mixture to 34 would resolve the purification issues. Doing so would both remove the species with a similar Rf to the cyclopropanes and prevent the accelerated elution of the Co(peroxo)(salen)-type species. It may then be possible to remove the

Co(O2)(salen)-type species simply by filtration through a pad of silica, obtaining the reaction mixture free of catalyst-derived species from the filtrate.

The first step of this approach was to develop a system that oxygenated any remaining

CoII(salen)-type catalyst in the cyclopropanation reaction mixture to the corresponding µ-peroxo-bridged dimer.

II The O2-binding activity of a Co complex is highly dependent on its crystal structure and physical state, with forms of the same species frequently being observed as ‘active’ or ‘inactive’ towards oxygenation.174 This has been demonstrated for the oxygenation of CoII(salen) by Appleton who showed that the complex existed in two visually distinct solid forms, a brown form which was active to oxygenation and a dark red form which was inactive to oxygenation.185 The inactive form existed as dimeric units where one cobalt atom interacted with an oxygen atom (Figure 28A). The active form also existed as dimeric units, however one cobalt atom was directly above the other (Figure 28B). The larger channels in the active form allowed oxygen to enter easily, facilitating oxygenation. When Co(salen) was dissolved in a donor solvent (e.g.

DMF, DMSO or pyridine) in the presence of molecular oxygen, [(solvent)Co(salen)]2O2 rapidly formed and precipitated as a dark brown solid.185

A) B)

N N N N Co X O O O O 2.26 Å 3.45 Å O O O O X N N Co N N

"inactive form" "active form" Figure 28: Reproduction of a scheme showing the ‘inactive’ and ‘active’ forms of solid CoII(salen) by Appleton185

It is well documented that the oxygenation of cobalt complexes is highly dependent on the solvent used, and that the oxygenation process is often reversible.174,175 Air is usually a competent enough oxidant to oxygenate CoII complexes, however when this 177 is not the case, pure O2 or H2O2 can be used. The most notable solvent properties that affect oxygenation are oxygen solubility,186 its ability to dissolve the cobalt species,172,187,188 and whether the solvent can facilitate oxygenation through coordination to the cobalt species.172,178,187,188,189 To begin this investigation, 10 mL of a variety of solvents were added to 10 mg samples of complex 28 and O2(g) was bubbled through (Table 17). Some solvent-catalyst systems showed almost immediate

oxygenation, such as i-hexane (entry 1), THF (entry 10), 2-MeTHF (entry 11) and DMF (entry 12). Notably, the properties of these solvents are in agreement with the necessary solvent properties mentioned previously, with THF, 2-MeTHF and DMF all being able to coordinate to cobalt, and i-hexane possessing an extremely high oxygen solubility.186 Interestingly, oxygenation in n-hexane (entry 2) proceeded much slower than in i-hexane (entry 1), suggesting a significant difference in solvation ability and/or oxygen solubility between these isomeric solvents. Given the widespread observation that amines can facilitate oxygenation of cobalt complexes owing to their propensity towards coordination, the effect of amines on the oxygenation of the cyclopropanation reaction mixture was investigated.172 Using pyridine as the solvent proved to give successful oxygenation (entry 13), however the addition of 10% Et3N to either Et2O (entry 14) or i-hexane (entry 15) proved to retard the oxygenation.

Table 17: The effect of solvent on the oxygenation of 28 to 34

N N Co t-Bu O O t-Bu

N N O2 t-BuO t-Bu Co t-Bu t-Bu t-Bu O O t-Bu Solvent, time O t-Bu O O t-Bu t-Bu t-Bu Co 28 N N

Entry Solvent Oxygenation observed? Time 1 i-Hexane Yes <10 s 2 n-Hexane Yes 1 min 3 Et2O Yes 2 min 4 EtOAc No - 5 TBME No - 6 CH2Cl2 Yes 2 h 7 Toluene No - 8 i-Propanol No - 9 Acetone No - 10 THF Yes <10s 11 2-MeTHF Yes <10s 12 DMF Yes <10s 13 Pyridine Yes <10s 14 Et2O (+10% Et3N) No - 15 i-Hexane (+10% Et3N) Yes 5 min

Ideally, in addition to facilitating the oxygenation of 28, the solvent would also allow direct filtration of the mixture to obtain the desired cyclopropane products whilst completely retaining the µ-peroxo-bridged dimer. This would require the use of a low-polarity solvent, as a high-polarity solvent would result in co-elution of all materials. It could be possible to perform the oxygenation in a high-polarity solvent, concentrate the mixture, re-dissolve in a lower-polarity solvent and filter the mixture, however concentration of the oxygenated mixture under reduced pressure presented the risk of driving off the O2 from at least some of the µ-peroxo-bridged dimer, resulting in the recovery of a mixture of Co species and making the oxygenation procedure pointless. Therefore, the criteria for an oxygenation solvent returned to one that both facilitated the oxygenation and was sufficiently non-polar to retain the µ-peroxo-bridged dimer during filtration. The solvent that performed optimally in both of these requirements was i-hexane (Table 17, entry 1).

Using i-hexane as the oxygenation solvent allowed successful oxygenation not only with pure O2 but also air. Using air is much more desirable than using pure O2 due to its significantly lower flammability.

Having developed a practical technique to remove the Co(salen)-type species from the reaction mixture and allow the cyclopropane products to be obtained cleanly, the possibility of recycling µ-peroxo-bridged dimer 34 to obtain CoII(salen)-type complex 28 was investigated. It has been observed that cobalt µ-peroxo-bridged dimers can release their bound O2 through either heating under reduced pressure or treatment with certain solvents such as benzene or chloroform.172,190 Based on these observations, a sample of CoII(salen)-type complex 28 was oxygenated with i-hexane to obtain the dark brown µ-peroxo-bridged dimer 34 after concentration. Dissolving this sample in chloroform and stirring at room temperature regenerated the vivid red CoII(salen)-type complex 28 along with concomitant gas evolution. Following on from this, a reaction mixture of the 28-catalysed cyclopropanation of PVS with EDA was oxygenated in i-hexane and then purified by silica chromatography to obtain samples of both the cyclopropane products and the µ-peroxo-bridged dimer. However, dissolving this sample of the µ-peroxo-bridged dimer in chloroform did not regenerate

CoII-catalyst 28. One possible reason for the lack of deoxygenation could be that residual material from the cyclopropanation reaction was hindering the loss of O2 from the µ-peroxo-bridged dimer. In 1977, Niswander and Taylor proposed a mechanism 191 whereby the O2 was ‘locked in’ by the coordination of an external ligand. This hypothesis was based on thermogravimetric analysis of a µ-peroxo-bridged dimer that possessed an external ligand on each cobalt atom which showed that the O2 and the external ligand (e.g. solvent) were lost from the cobalt complex at approximately the same temperature.191 In the case of the sample from the cyclopropanation of PVS and

EDA, the external ligand could reasonably be either H2O or excess PVS. The opposition towards µ-peroxo-bridged dimer deoxygenation was observed for samples of the µ-peroxo-bridged dimer from cyclopropanations run on H2O and neat, however this does not rule out H2O as a potential external ligand. This is because there were routes through which the µ-peroxo-bridged dimer could become exposed to H2O even with the neat reaction, including from the atmosphere or the solvent during work-up and chromatography. Alternatively, PVS may be acting as an external ligand, stabilising the µ-peroxo-bridged dimer. An excess of 0.5 equivalents of PVS (with respect to EDA) was used in the cyclopropanation reaction to compensate for loss through thermal polymerisation. With a catalyst loading of 5 mol%, there was likely an abundance (with respect to the catalyst) of PVS remaining which may be implicated in the stabilisation of the µ-peroxo-bridged dimer during deoxygenation conditions.

In conclusion, a practical technique has been developed to remove the Co(salen)-type species from the cyclopropanation reaction mixture and in doing so allows the cyclopropane products to be obtained cleanly.

2.1.3.3. Open-Flask CoII-Catalysed Cyclopropanation With optimised cyclopropanation and oxygenative work-up conditions in hand, effort was directed to try to make the cyclopropanation reaction protocol safer and simpler by performing the reaction under an air atmosphere. Whilst the CoII-catalysed cyclopropanation displayed no sudden N2(g) evolution when conducted on H2O even at the largest scale reactions conducted (utilising 40 mmol of EDA), by conducting the

reaction in an open flask N2(g) evolution would not be a safety issue, making the approach even more desirable, particularly for large-scale industrial applications.

One potential problem with having the CoII-catalysed cyclopropanation run under an air atmosphere was that CoII catalyst 28 may potentially undergo oxygenation when under an oxygen-containing atmosphere, reducing the amount of active catalyst in the reaction. Conducting a 5.0 mmol scale cyclopropanation reaction using the optimised conditions from Section 2.1.3.1, except this time in a flask open to air, gave a greatly reduced yield of 25% (Table 18, entry 1). Conducting the reaction in the absence of solvent gave a much higher yield of 48% (entry 2), however this was notably lower than the 60% yield obtained under an argon atmosphere (Table 15, entry 5). Due to the observation that chloroform facilitates the deoxygenation of Co µ-peroxo-dimers, chloroform was tested as a reaction solvent under an air atmosphere, with reflux condensers being fitted to prevent solvent loss through evaporation. Whilst a 1.0 M concentration of chloroform gave a poor yield (Table 18, entry 3), a significant increase was observed upon increasing the concentration to 10.0 M (Table 18, entry 4).

Table 18: Solvent effects on the open-flask CoII-catalysed cyclopropanation of PVS with EDA

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O EtO O EtO O (5.0 mol%) S EtO Ph Solvent, 40 °C, 24 h Ph Ph N2 S S 5.0 mmol (1.5 equiv) 15 16

Entry Solvent PVS recovery Yield (%) trans + cis (%) a 1 H2O 1.16 25

2 Neat 0.39 48 a 3 CHCl3 0.15 26 b 4 CHCl3 0.38 54 Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). a Concentration = 1.0 M. b Concentration = 10.0 M.

An alternative approach was explored whereby the reactants were dissolved in a dense organic phase which was then shielded from the atmosphere by a layer of less dense H2O (Figure 29). The hypothesis was that, provided the stirring was not so vigorous as to create a vortex within the mixture, the H2O phase would shield the cyclopropanation reaction mixture from the O2-containing atmosphere but the N2 evolved from the reaction would be free to escape. Solvents that have a higher density than H2O primarily include chlorinated solvents, which have been shown to be capable of facilitating the deoxygenation of Co µ-peroxo-dimers; a desirable attribute for this objective.

H O phase HH22O2O phase phase HigherHigherHigher densitydensity density organicorganic organic phasephase phase StirrerStirrerStirrer barbar bar

Figure 29: Reaction set-up for the biphasic air-atmosphere CoII-catalysed cyclopropanation of PVS with EDA

To see which chlorinated solvent would be optimum for the cyclopropanation reaction, a sample of the solvent screen from Table 14 is shown (Table 19). The highest yielding chlorinated solvent was chlorobenzene (Table 19, entry 6).

Table 19: The effectiveness of chlorinated solvents in the CoII-catalysed cyclopropanation of PVS with EDA

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O EtO O EtO O (5.0 mol%) S EtO Ph Solvent (0.2 M), 40 °C, 24 h Ph Ph N2 S S 0.3 mmol (1.5 equiv) 15 16

Entry Solvent PVS recovery dr Yield (equiv) trans:cis trans + cis (%)

1 CH2Cl2 0.09 52:48 40 2 CHCl3 0.58 48:52 13

3 CCl4 0.74 - 0 4 1,2-Dichloroethane 0.17 47:53 41 5 1,2-Dichlorobenzene 0.62 50:50 38 6 PhCl 0.50 50:50 50 Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene). Diastereoselectivity was determined by 1H NMR spectroscopy.

The cyclopropanation reaction was set up according to Figure 29 using a biphasic solvent system of chlorobenzene and H2O (Table 20, entry 1). For comparison, the reaction was also set up without the H2O phase (entry 2), and the open-flask reactions on H2O (entry 3) and neat (entry 4) are also shown. The use of chlorobenzene and

H2O gave a poor yield (entry 1), however it was much higher than that of just chlorobenzene (entry 2). The use of a neat system however proved superior, giving a yield of 48% (entry 4).

Table 20: The CoII-catalysed cyclopropanation of PVS with EDA under an air atmosphere

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O EtO O EtO O (5.0 mol%) S EtO Ph Solvent, 40 C, 24 h N ° Ph Ph 2 Open-air atmosphere S S 5.0 mmol (1.5 equiv) 15 16

Entry Solvent PVS recovery Yield (equiv) trans + cis (%)

1 PhCl (1.0 M) with H2O (20 mL, 0.25 M) 0.85 38 2 PhCl (1.0 M) 0.78 14

3 H2O (1.0 M) 1.16 25 4 No solvent 0.39 48 Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene).

Success had been obtained in achieving a reasonable yield of the desired cyclopropanes through a CoII-catalysed cyclopropanation under an air atmosphere. The optimum yield obtained of 48% was, however, significantly lower than when the reaction was conducted under an Ar(g) atmosphere. For this reason, the open-flask cyclopropanation was not investigated further. The cyclopropanation conditions developed in Section 2.1.3.1 continued to be used as the optimised cyclopropanation methodology for upcoming cyclopropanation reactions.

2.1.3.4. Cyclopropanation of Alternative Reagents The developed cyclopropanation methodology gave access to large quantities of the cyclopropyl sulfide scaffolds 15 and 16. These scaffolds were hugely important to the project because both the ester and sulfide functionalities offered a variety of derivatisation possibilities. The phenyl sulfide functionality presented a group which is well tolerated in biology and could give facile access to oxidised functionalities including sulfoxides and sulfones, both of which also have a significant presence in medicinal chemistry. The sulfoxide functionality also presents the opportunity for derivatisation of the intact cyclopropane ring through a sulfoxide-metal exchange protocol. For projects that would definitely utilise a sulfoxide-metal exchange protocol,

it could be advantageous if cyclopropyl sulfoxides 35 and 36 could be formed directly through the cyclopropanation of phenyl vinyl sulfoxide (Scheme 27). However, when using the optimised conditions developed for the 28-catalysed cyclopropanation of phenyl vinyl sulfide with EDA, the reaction with phenyl vinyl sulfoxide was unsuccessful, producing no cyclopropane-containing products. This was attributed to the alkene of phenyl vinyl sulfoxide being too electron-deficient for reaction with the carbon-centred radical of the cobalt complex resulting from EDA binding to 28, preventing the cyclopropanation reaction.

N N Co t-Bu O O t-Bu

t-Bu t-Bu EtO O 28 EtO O O O (5.0 mol%) EtO S Ph Ph , 40 S S N Ph H2O (0.2 M) °C, 24 h 2 O O (1.5 equiv) 35 36 Scheme 27: Attempted CoII-catalysed cyclopropanation of phenyl vinyl sulfoxide with EDA

In order to gain more information on the alkene requirements of the cyclopropanation reaction, vinyl sulfides with significantly different steric and electronic properties were examined. With this aim in mind, vinyl sulfides with substitution on the aryl ring were targeted, namely o-Me, o-CF3, p-Cl, p-CF3 and p-OMe. Oxidation of the substituted aryl thiols using a procedure published by Alam and co-workers192 gave the corresponding disulfides in almost quantitative yields (Table 21, entries 1–4). The p-OMe substituted aryl disulfide was not synthesised from the corresponding thiol as it was commercially available. Treating the disulfides with vinyl magnesium bromide generated the vinyl sulfides (entries 5–9). Vinyl sulfides are known to be susceptible to polymerisation on silica and thermally induced polymerisation, causing difficulties with their isolation. Electron-rich vinyl sulfides appeared to be more stable during silica chromatography than high pH reverse-phase chromatography (entries 5 and 9) in contrast to electron-deficient vinyl sulfides which responded better to high pH reverse phase chromatography (entries 6 and 8). The p-Cl substituted vinyl sulfide was

sufficiently pure to be taken on without further purification (entry 7), though based on the observed trends it would be expected that high pH reverse-phase chromatography would be a reasonable purification method if required.

Table 21: Oxidative formation of symmetrical disulfides followed by vinyl sulfide synthesis

Br N O N O Br BrMg SH R S (0.25 equiv) S (1.5-2.0 equiv) S R CHCl3 (0.1 M), rt, 2-21 h THF (0.12 M), 0 ºC, 3-4 h R R R = o-Me 37 R = o-Me 41 R = o-CF3 38 R = o-CF3 42 R = p-Cl 39 R = p-Cl 43 R = p-CF3 40 R = p-CF3 44 R = p-OMe 45 Entry R Yield Entry R Yield Disulfide (%) Vinyl sulfide (%) a b 1 o-Me 99 5 o-Me 35 (8 ) b 2 o-CF3 99 6 o-CF3 73 3 p-Cl 98 7 p-Cl 83c b 4 p-CF3 96 8 p-CF3 38 9 p-OMe 13a a Isolated by silica chromatography. b Isolated by high pH reverse phase chromatography. c Product was sufficiently pure after work-up to be used without further purification.

The o-CF3, p-Cl and the p-CF3 substituted phenyl vinyl sulfides were subjected to the neat reaction conditions. Cyclopropanation of these electron-poor vinyl sulfides occurred in very low yields (Table 22). The cyclopropanation appeared to favour the trans-diastereoisomer upon addition of an electron withdrawing group at the para position of the aromatic ring, however this could be an artefact resulting from calculating diastereoselectivity from such low yields of products and remains unconfirmed.

Table 22: CoII-catalysed cyclopropanation of phenyl vinyl sulfide derivatives with substitution on the aryl ring

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O EtO O EtO O S (5.0 mol%)

EtO R R R Neat, 40 °C, 24 h N2 S S (1.5 equiv)

R = o-CF3 42 46 47 R = p-Cl 43 48 49 R = p-CF3 44 50 51

Entry R Vinyl sulfide recovery dr Yield (equiv) (trans:cis) trans + cis (%)

1 o-CF3 1.26 51:49 8 2 p-Cl 0.43 67:33 3

3 p-CF3 0.71 65:35 1

Yields were determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene or dibenzyl ether).

To investigate the effect of steric bulk on the diazo reagent in the cyclopropanation reaction, tert-butyl diazoacetate (t-BDA) was tested using the optimised conditions. With the potential for the difference in lipophilicity between EDA and t-BDA to result in different behaviour during the reaction, the reaction was explored using neat conditions, H2O and cyclohexane (Table 23). The reaction proceeded best in H2O (entry 2), giving a 76% yield of the t-butyl ester-substituted cyclopropanes 52 and 53. The use of t-BDA gave a slight preference towards formation of the trans-cyclopropane diastereoisomer 52. In all solvents tested, the cyclopropanation of t-BDA gave lower yields than that of EDA (Table 23, entries 1–3 and Table 14, entries 11, 17 and 18). In addition, t-BDA is a much more expensive reagent than EDA. For these reasons, cyclopropanation of t-BDA was not pursued further.

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Table 23: CoII-catalysed cyclopropanation of PVS with t-BDA

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O t-BuO O t-BuO O S (5.0 mol%) t-BuO Solvent (0.2 M), 40 °C, 24 h N2 S S (0.3 mmol) (1.5 equiv) 52 53

Entry Solvent PVS recovery trans:cis (dr) trans + cis (%) (equiv) 1 Neat 0.88 58:42 19 2 H2O 0.56 57:43 76 3 Cyclohexane 0.86 54:46 38

All yields were determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene or dibenzyl ether).

2.1.3.5. Conclusions The first transition metal-catalysed cyclopropanations of PVS with EDA have been developed, initially using CuI and later, more successfully, utilising CoII. This enabled the practical synthesis of the desired trans- and cis-bifunctional cyclopropyl scaffolds 15 and 16. The CoII-catalysed cyclopropanation has been demonstrated on a 40 mmol scale, generating almost 8 g of cyclopropanes in an 89% yield. The CoII(salen)-type catalyst 28 is air and moisture stable and it does not cause dimerisation of the diazo reagent, meaning that a glovebox and syringe pump are not required. A facile oxygenative work-up procedure was developed to facilitate the purification of the cyclopropane-containing products. An open-flask CoII-catalysed cyclopropanation procedure was developed, however with a maximum yield of 48% achieved, it was not utilised. The optimised CoII-catalysed cyclopropanation conditions gave low yields when applied to alkenes that were more electron-deficient than PVS. The sterically bulky diazo compound t-BDA gave very good yields under the optimised conditions. The cyclopropanation conditions developed in Section 2.1.3.1 continued to be used as the optimised cyclopropanation methodology for upcoming cyclopropanation reactions.

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2.1.4. Asymmetric Transition Metal-Catalysed Cyclopropanation Asymmetric cyclopropanation reactions have been of huge interest ever since the first example in 1966 by the Nozaki group using chiral salicylaldimine ligands.153 The enantioenrichment in the cyclopropane products was very low, however it demonstrated that metal-catalysed cyclopropanation reactions could effect enantioselective control through the incorporation of chiral ligands.

Since then a wide variety of transition metals have demonstrated the capability to catalyse enantioselective cyclopropanation reactions through the incorporation of enantioenriched ligands (Schemes 28–30).

One notable example was produced by the Evans group, performing an asymmetric CuI-catalysed cyclopropanation using a chiral BOX ligand to obtain the product cyclopropanes in excellent yields and enantioselectivity, and with moderate diastereoselectivity (Scheme 28A).105 Examples of asymmetric ruthenium-catalysed cyclopropanations have been developed by the Nishiyama group107 utilising a PyBOX ligand (Scheme 28B) and by the Miller group108 using a salen-type complex (Scheme 28C).

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O O N N t-Bu t-Bu (1.04 mol%)

CO2Et CO2Et EtO2C CuOTf (1 mol%) Ph N2 CHCl , 25 ºC (5 equiv) 3 Ph Ph 18 19 99% ee 97% ee 77% yield (18 + 19) trans:cis = 73:27

O O N N N i-Pr i-Pr (7 mol%)

[RuCl2(p-cymene)]2 CO2Me CO2Me MeO2C (2.5 mol%) Ph N2 CH Cl , 30−35 ºC, 20 h (5 equiv) 2 2 Ph Ph 54 55 92% ee 97% ee 82% yield (54 + 55) trans:cis = 89:11

py N N Ru t-Bu O py O t-Bu

t-Bu t-Bu CO2Et CO2Et EtO2C (1 mol%) OEt N2 CH2Cl2, rt, 12 h (5 equiv) OEt OEt 56 57 69% ee 78% ee 80% yield (56 + 57) trans:cis = 80:20 Scheme 28: Asymmetric transition metal-catalysed cyclopropanation reactions

An example of asymmetric rhodium-catalysed cyclopropanation has been demonstrated by the Davies group using a ‘paddle wheel’ complex to obtain trifunctionalised cyclopropanes in excellent yields and with extremely high enantioselectivity (Scheme 29A).106 Asymmetric palladium-catalysed cyclopropanation was attempted by the Denmark group, however despite the reaction proceeding in excellent yields with a variety of chiral complexes, the cyclopropane

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products were racemic (Scheme 29B).193 After product decomposition and racemisation were ruled out experimentally, the lack of enantio-induction was attributed to either partial or complete decomplexation of the chiral ligand during the course of the reaction.

N RO2S H R = C H O O 12 25 O O N RO S H 2 Rh Rh SO2R N O O O O H H N SO2R

Cl (1 mol%) CO2Me CO2Me pentane, −78 ºC N2 (2 equiv) Cl 70% yield >97% ee

B) O O

N N Pd Cl Cl O Me O (1 mol%) CH2 Me N2 CH2Cl2, Et2O, 0 ºC–rt (4 equiv) 93% yield <2% ee Scheme 29: Examples of asymmetric rhodium- and palladium-catalysed cyclopropanation reactions

Katsuki developed a salen-type/BINOL-derived ligand which when used in a CoII-catalysed cyclopropanation gave excellent yields and enantioselectivities and was highly cis-selective (Scheme 30A).110 Asymmetric CoII-catalysed cyclopropanation has also been demonstrated by Zhang with a chiral porphyrin CoII complex to synthesise a wide variety of trisubstituted cyclopropanes in excellent yields, enantioselectivities and cis-diastereoselectivity (Scheme 30B).111

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N N Co O O Ph Ph

(5 mol%) CO2t-Bu

t-BuO2C OMe NMI (10 mol%)

N2 THF, rt, 24 h (5 equiv) OMe 94% yield cis:trans = 98:2 ee (cis) = 97% (absolute configuration was not determined)

B) H H

O O NH Ar HN t-Bu N N Co Ar = N N

NH Ar HN t-Bu O O

H H NC CO2t-Bu NC CO2t-Bu O (1 mol%) NMe2 N2 NMe2 n-hexane, -20 ºC, 24 h O (1.2 equiv) 99% yield cis:trans >99:1 87% ee Scheme 30: Examples of asymmetric cobalt-catalysed cyclopropanation reactions

It is notable that the vast majority of successful asymmetric cyclopropanations have been carried out on substrates with limited conformational flexibility in the vicinity of the alkene, predominantly using styrene-derivatives but also including acrylates, acrylamides, vinyl ethers and vinyl amines. These substrates delocalise electron density between the alkene and the adjacent oxygen/nitrogen heteroatom or aromatic ring due to the efficient orbital overlap between the C 2� and C/N/O 2� orbitals, with the stabilisation resulting in restricted rotation about the C-C/N/O s-bond. These compounds are more successful in asymmetric cyclopropanations as a result of the increased rigidity of the alkene. This increased rigidity allows the chiral information of the chirality source to be transferred to the cyclopropanation transition state more

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efficiently, enabling greater enantioenrichment in the product cyclopropanes. In contrast, there is free rotation around the two C-S s-bonds of PVS at 25 °C, giving significant conformational flexibility around the alkene (Figure 30).194,195

Figure 30: Relevant modes of bond rotation present in PVS

A rare and important example of a transition metal-catalysed cyclopropanation of a vinyl sulfide by diazo-derived carbene insertion into an alkene was reported by White and Shaw in 2014, who developed an enantioenriched chiral CoII catalyst to cyclopropanate a variety of 1,1-substituted alkenes.139 The cyclopropanation gave an excellent yield, high diastereoselectivity and high enantioselectivity with the 1,1-substituted vinyl sulfide example (Scheme 25), though all three values were significantly lower than those obtained for the rest of the alkene scope. With respect to the stereoselectivity, it is significant that the presence of the n-propyl chain on the vinyl sulfide would sterically hinder the rotation of the thiophenyl group.

2.1.4.1. Asymmetric CuI-Catalysed Cyclopropanation of PVS with EDA A considerable amount of success has been achieved in the field of CuI-catalysed asymmetric cyclopropanation. A notable example was produced by the Evans group which used a CuI(BOX) catalyst (Scheme 31A).105 In fact, CuI salts and bisoxazoline-derived ligands have proved to be a particularly effective combination for asymmetric cyclopropanation (Scheme 31).196,197

106

A) O O N N Ph Ph (3.5 mol%) TMS TMS Br CuOTf (1.7 mol%)

N2 CH2Cl2, rt, 17 h (10.0 equiv) Br 86% yield ee = 66% B)

O O N N R R (3.7 mol%) R = i-Pr R = t-Bu CO2Et EtO2C Ph CuOTf (2.9 mol%) 81% yield 62% yield F dr = 68:32 dr = 72:28 N2 F CH2Cl2, 40 ºC, 6–7 h ee (cis) = 69% ee (cis) = 89% Ph ee (trans) = 54% ee (trans) = 80% (1.5 equiv)

Scheme 31: CuI-catalysed cyclopropanation reactions utilising CuI(BOX) catalytic systems. A).105 B).197

The proposed mechanism of stereo- and enantio-induction was detailed by Haufe and co-workers, using a fluorostyrene substrate as an example (Schemes 31B and 32).197 The substituents on the carbene carbon are perpendicular to the plane of the BOX ligand. When the alkene approaches the CuI(carbene)(BOX) complex, a number of steric interactions take place, contributing to the transition state energy for the formation of each cyclopropane isomer. The interactions between the substituents on the alkene and the substituents on the carbene (Scheme 32) are significant in determining which diastereoisomer is favoured. The asymmetric induction was explained by an interaction between the carbene substituents and the BOX ligand. In the case of attack of the olefin on the si face of the carbene (Scheme 32A), a steric interaction with the bulky R group of the BOX ligand would hinder the rotation of the ester group into the plane necessary for cyclopropane formation. Since such an interaction is absent for the alkene attacking the re face of the carbene (Scheme 32B), the latter is favoured. Selectivity was observed to increase as R increased in size. The gem-dimethyl group on the BOX ligand acts to fine-tune the bite angle between the nitrogen donor atoms and the copper metal.

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A) minor enantiomer R

CO2Et O F CO2t-Bu N CH3 Cu F N CH Ph H H O 3 R Ph

B) Ph major enantiomer R F CO2Et O Ph CO2t-Bu N CH3 Cu N CH F H H O 3 R Scheme 32: Proposed mechanism for asymmetric CuI(BOX)-catalysed cyclopropanation197

A structurally similar type of complex is derived from the PyBOX ligand. Such Cu(PyBOX) complexes have also been utilised in asymmetric cyclopropanations of various alkenes (Scheme 33).198

Ph O O Ph N Ph N Cu N Ph TfO OTf

CO2t-Bu CO2t-Bu CO2t-Bu (1 mol%) Ph N2 CHCl3, 25 ºC, 21 h (4.0 equiv) Ph Ph 58 59 35% ee 6% ee 80% yield (58 + 59) trans:cis = 70:30

Scheme 33: CuIIPyBOX-catalysed asymmetric cyclopropanation of styrene198

With a considerable number of CuI(BOX)-catalysed cyclopropanation examples present in the literature, a range of BOX ligands were tested with the optimised CuI-catalysed cyclopropanation conditions for PVS and EDA (Table 24, entries 1–5). The ligands were chosen so that they possessed a variety of side-arms and investigated whether the gem-dimethyl motif was beneficial to the cyclopropanation.

Ligand 17 had been used in the optimisation of the CuI-catalysed reaction and was found to generate no observable enantioselectivity for the trans-diastereoisomer

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(Table 24, entry 1). Insufficient material was obtained for the cis-diastereoisomer to obtain an enantioselectivity value, denoted by a dash in Table 24. The slight variation in yield between entry 1 and previous entries in the optimisation of the cyclopropanation reaction (Table 12, entry 18) was due to the capricious nature of the CuI-catalysed reaction. Changing the i-Pr ligand arms to the more sterically bulky t-Bu produced a very small amount of enantioselectivity (entry 2). Removal of the gem-dimethyl groups on the ligand had very little effect on the yield or selectivity of the reaction (entry 3). Introducing phenyl ring substituents onto the ligand increased the selectivity, though it still remained < 10% ee (entry 4). Benzyl ligand arms resulted in a decrease in enantioselectivity (entry 5) compared to t-Bu (entry 2) and phenyl (entry 4). There was very little variation in the yield and diastereoselectivity of the cyclopropanation reaction with these BOX ligands, despite the significantly different steric bulk of the various ligand arms. A PyBOX ligand was tested due to the observation that enantioenriched chiral Cu(PyBOX) catalytic systems are capable of transferring chiral information during cyclopropanation reactions,198 however this resulted in very low enantioselectivity, extremely low diastereoselectivity and a yield of only 20% (entry 6).

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Table 24: CuI-catalysed enantioselective cyclopropanation of PVS with EDA

O CuOTf (1 mol%) EtO O EtO O Ligand (1.1 mol%) S EtO Ph CHCl3 (0.14 M), 30 °C, 24 h Ph Ph N2 S S (2.0 equiv) 15* 16*

O O O O O O N N N N N N i-Pr i-Pr t-Bu t-Bu t-Bu t-Bu 17 60 61

O O O O N N O O N N N Ph Ph N N Ph Ph i-Pr i-Pr 62 63 64

Entry Ligand Diazo ee ee dr Yield dimerisation (%) (trans) (cis) trans:cis trans + cis (%)

1 1 13 0 - 53:47 40 2 2 18 3 2 53:47 37 3 3 7 3 2 51:49 35 4 4 23 7 6 51:49 34 5 5 3 2 - 54:46 37 6 6 7 3 - 53:47 20 Yields determined by 1H NMR spectroscopy with comparison to internal standard (1,3,5-trimethoxybenzene).

Due to the lack of success in developing a valuable asymmetric CuI-catalysed cyclopropanation reaction, the use of enantioenriched CoII(salen)-type catalysts was investigated.

2.1.4.2. Asymmetric CoII-Catalysed Cyclopropanation of PVS with EDA Enantioenriched chiral CoII(salen)-type complexes have been widely utilised in asymmetric syntheses, including asymmetric cyclopropanation.110,139,199 Chiral salen-type complexes contain one or more element of chirality on the ligand, with the carbon numbering for the salen-type skeleton shown in Figure 31. Insight into the mechanisms of chiral induction by enantioenriched chiral salen-type complexes has been developed through notable contributions by the Jacobsen group and the Katsuki group. The presence of a chiral diamine backbone causes the complex to possess a ‘stepped’ conformation, with one aromatic ring of the salen-type complex protruding

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below the plane of the coordinated transition metal and one aromatic ring protruding above (Scheme 34).200,201,202 When the diazo species reacts with the transition metal with concomitant release of N2, the most sterically bulky substituent on the carbene carbon is directed towards the downwards-facing side of the complex to reduce unfavourable interactions.200

8 8'

7 N N 7' 6 1 1' 6' 2 M 2' 5 O O 5' 4 3 3' 4' 9 9' Figure 31: Carbon numbering for the salen-type complex skeleton

The successful approach trajectory of the alkene is subject to debate, with three likely possibilities having been identified. It is widely recognised that the alkene takes a side-on perpendicular approach towards the transition metal complex.203,204,205,206 For all three alkene approach trajectories a common requirement for enantioselectivity is the inclusion of bulky substituents on the ligand to prevent the alkene approaching from the opposite side to the diamine (Scheme 34, approach c and Scheme 35, approach g).203,207

The first two approaches were described by Jacobsen and were dependent upon the ligand employed.203 When a bulky diamine backbone such as a chiral 1,2-diphenylethylenediamine is used, approach d is blocked off. The presence of a chiral diamine results in the complex adopting a ‘stepped’ conformation, and the alkene attacks from the ‘downward’ facing aromatic ring as it is more accessible (approach a).203

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Ph O M O Ph

Front-on view

(Disfavoured)

Ph Ph Ph H (Favoured) N N (Disfavoured) M a Me O O Me b Me H t-Bu t-Bu

(Disfavoured) Scheme 34: Explanation of enantioselectivity of chiral 1,2-diphenylethylenediamine-derived salen-type complexes

The second approach described by Jacobsen is applicable when a less sterically bulky diamine such as a 1,2-diaminocyclohexane is used, and bulky groups on the salicylaldehyde-derived section of the complex prevent approaches g, e and f (Scheme 35).203 In this circumstance attack from the side of the chiral diamine is possible (approach h).203

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O M O

H Front-on view

Ph Me

H H

(Favoured)

H H (Disfavoured) N N (Disfavoured) M e t-Bu O O t-Bu f

t-Bu t-Bu

(Disfavoured) Scheme 35: Explanation of enantioselectivity of chiral 1,2-diaminocyclohexane-derived salen-type complexes

An alternative alkene approach has been described by Katsuki that incorporated electronic effects.207 The observation that conjugated alkenes generally gave higher enantioselectivities than alkyl-substituted alkenes led to the proposal that repulsive p-p interactions also played a part in determining the enantioselectivity of the cyclopropanation by affecting alkene orientation during its approach.207 As an alkene approaches the transition metal complex along trajectory l (Scheme 36), it is exposed to a different electronic environment operating on either side of the N---M axis. The salicylaldehyde-derived component of the ligand is rich in p-electrons whereas the aliphatic diamine component has no p-electrons. Therefore, alkenes that possess substituents that are rich in p-electrons such as styrenes suffer p-p electronic repulsion which directs the p-electron-rich substituent towards the cyclohexyl part of the complex. This mechanistic approach predicts that alkenes bearing a substituent that is both p-electron rich and sterically bulky will generally elicit high enantioselectivity as a result of the synergistic alkene-orienting effects of p-p repulsive interactions and steric repulsion between the alkene substituents and the complex. This explains why

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styrene-derivatives are frequently shown to give extremely high enantioselectivities in asymmetric salen-type complex-catalysed cyclopropanation reactions.164

O M O

H Front-on view

RL H R S (Favoured) H

l H H (Disfavoured) N N (Disfavoured) M i O O j

Me Et Ar Me H Ar Et H k

(Disfavoured)

Ar = t-Bu

Scheme 36: Katsuki’s explanation for the enantioselectivity of chiral salen-type complexes207

It was observed that the enantioselectivity of cis-alkenes was controlled principally by the chiral diamine backbone whereas the enantioselectivity of trans-alkenes was largely dictated by chirality attached at the C9 and C9’ positions.208 This was proposed to be due to cis-alkenes approaching the complex parallel to the plane of the complex, whereas trans-alkenes approach diagonally from above the complex to minimise steric clash of the alkene substituents with the complex (Figure 32A).208 These different trajectories result in cis- and trans-alkenes being influenced differently by chirality at different positions on the complex (Figure 32B).208

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A) B) H RL

RS H

R N O M Ar RS RL N O Et N N H H H M Me O O

Figure 32: A) The different proposed alkene trajectories for cis- and trans-alkenes towards salen-type complexes.208 B) Approximate regions of influence for chirality at the C8 (and C8’) and the C9 (and C9’) carbons. C’ functionalities have been removed for visual clarity.208

In all cases the asymmetric induction is dependent on a combination of factors being fulfilled; the induction of a conformational preference for the diazo-derived component through a ‘stepped’ complex, the selection of an alkene approach trajectory through appropriate ligand structure, and obtaining facial selectivity of the incoming alkene through appropriate ligand structure.

With the success of the racemic cyclopropanation of PVS with EDA catalysed by CoII complex 28, an enantiopure variant of 28 was obtained commercially, and a variety of structurally-related enantiopure CoII(salen)-type complexes were synthesised that would investigate the effects of catalyst steric bulk and electronic properties on the asymmetric cyclopropanation of PVS with EDA (Scheme 37). These enantiopure complexes were used in neat asymmetric CoII-catalysed cyclopropanation reactions of PVS with EDA (Table 25). The major enantiomeric products were (1S,2R)-15 and (1S,2S)-16, determined through comparison of chiral HPLC data with that of enantiopure material whose configuration had been confirmed by X-ray crystallography (Section 2.1.4.3). Enantiopure complex 28* gave a reasonable enantioenrichment of 40% for the trans-diastereoisomer and a good enantioenrichment of 64% for the cis-diastereoisomer (Table 25, entry 1). Replacement of the 1,2-diaminocyclohexane backbone with a 1,2-diphenylethylenediamine backbone drastically reduced the yield to 6% and significantly reduced the enantioselectivity for both diastereoisomers (entry 2). The reduction in yield was likely attributed to all alkene approaches being blocked by either the t-Bu groups on the salicylaldehyde component or the phenyl groups of the diamine component.

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H2N NH2 EtOH (0.06 M) O reflux, 20 h 61% N N t-Bu OH Co 2) Co(OAc) 2 t-Bu O O t-Bu t-Bu (1.0 equiv) (2.0 equiv) EtOH, H2O, toluene t-Bu t-Bu reflux, 3 h 66 75%

N N N N

Co(OAc)2 (1.0 equiv) Co t-Bu OH HO t-Bu t-Bu O O t-Bu EtOH (0.08 M) reflux, 17 h N N 14% N N

O O O 68 O

N N Co(OAc)2 (1.0 equiv) N N Co OH HO EtOH (0.05 M) O O reflux, 17 h 14% OH HO OH HO 69

H2N NH2 EtOH (0.07 M) O reflux, 3 h 98% N N OH Co 2) Co(OAc) 2 O O OEt (1.0 equiv) (2.0 equiv) EtOH, H2O, toluene OEt EtO reflux, 3 h 71 88%

1) NCS (2.12 equiv) AcOH (0.26 M) reflux, 17 h 71% 2)

H2N NH2 (0.5 equiv) EtOH (0.03 M) O reflux, 3.5 h 97% Cl N N Cl OH Co 3) Co(OAc) 2 Cl O O Cl OEt (1.0 equiv) (2.0 equiv) EtOH, H2O, toluene OEt EtO reflux, 1 h 74 54%

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H2N NH2 EtOH (0.08 M) O reflux, 3.5 h 81% N N I OH Co 2) Co(OAc) 2 I O O I I (1.0 equiv) (2.0 equiv) EtOH, H2O, toluene I I reflux, 3 h 76 45% Scheme 37: Synthesis of enantiopure chiral CoII(salen)-type complexes. The synthesis of 66 proceeded via Schiff base 65, 71 proceeded via Schiff base 70, 74 proceeded via aldehyde 72 and Schiff base 73, and 76 proceeded via Schiff base 75.

CoIIsalen (67) possessed far less steric bulk than complexes 28* and 66 and due to an absence of chirality would not result in enantioenriched cyclopropanes, however it was of interest to observe how a lack of steric bulk around the catalyst affected catalytic performance in the cyclopropanation reaction. A significant decrease in yield was observed compared to 28*, however it did show that even such a rudimentary ligand was able to give a reasonable yield of the desired cyclopropanes. Next, complex 68 was examined (entry 4), possessing the 1,2-diaminocyclohexane backbone and an intermediate steric bulk between complexes 28* and 67. Complex 68 gave extremely low yields and there was not enough cyclopropane-containing material generated to obtain enantioselectivity data. Complex 69 possessed alcohol functionality and very little steric bulk around the complex, and gave an extremely low yield of cyclopropanes (entry 5). The ethyl diether variant, complex 71, gave a slightly higher yield and reasonable enantioselectivity for both diastereoisomers (entry 6). Carreira has demonstrated that chlorinated salen-type complexes similar to complex 74 can give higher yields in transition metal-catalysed cyclopropanation reactions than their non-chlorinated counterparts.209 Using the methodology described by Carreira and co-workers,209 the tetrachlorinated analogue of complex 71 was synthesised and tested, with the increased steric bulk and reduced electron-richness resulting in a significantly reduced yield (entry 7). Synthesis of the electron-poor tetraiodo CoII(salen)-type complex 76 gave a low yield of cyclopropanes with low enantioselectivities for both trans and cis diastereoisomers.

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Table 25: The effect of enantiopure chiral catalyst structure on the enantioselective cyclopropanation of PVS with EDA

O EtO O EtO O CoII complex (5 mol%) S EtO Ph neat, 40 ºC, 24 h Ph Ph N2 S S 0.3 mmol (1.5 equiv) 15* 16*

N N N N N N Co Co t-Bu O O t-Bu Co O O t-Bu O O t-Bu t-Bu t-Bu t-Bu t-Bu 28* 66 67

N N Co N N N N t-Bu O O t-Bu Co Co O O O O N N OH HO OEt EtO O 68 O 69 71

Cl N N Cl N N Co Co Cl O O Cl I O O I

OEt EtO I I 74 76

Entry Complex ee ee dr Yield (trans) (cis) trans:cis trans + cis (%)

1 28* 40 64 47:53 100 2 66 32 42 44:56 6 3 67 - - 48:52 40 4 68 - - 49:51 5 5 69 - - 43:57 6 6 71 51 57 49:51 17 7 74 - - 57:43 4 8 76 29 23 50:50 9

Yields determined by 1H NMR spectroscopy with comparison to internal standard (dibenzyl ether). Diastereoselectivity was determined by 1H NMR spectroscopy. As illustrated, the major enantiomeric products were (1S,2R)-15 and (1S,2S)-16.

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After generating and testing a diverse range of highly enantioenriched CoII-containing salen-type complexes in the cyclopropanation of PVS with EDA (Table 25) it was apparent that complex 28* gave the most promising overall asymmetric cyclopropanation, determined as a combination of giving the highest yield of products and inducing some of the highest enantioselectivities. The effect of reaction solvent and temperature using complex 28* was therefore investigated to try to optimise this asymmetric cyclopropanation further (Table 26). A solvent screen was conducted on a range of solvents with very different properties (Table 26). From this it was clear that conducting the reaction in cyclohexane produced the highest enantioselectivities in a reasonable yield (entry 4), and conducting the reaction on H2O gave the highest yield with reasonably good enantioselectivity observed (entry 5).

Table 26: Solvent effects on the asymmetric 28*-catalysed cyclopropanation of PVS with EDA

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28* O EtO O EtO O (5.0 mol%) S EtO Ph Solvent (0.2 M), 40 ºC, 24 h Ph Ph N2 S S (1.5 equiv) 15* 16*

Entry Solvent ee ee dr Yield (trans) (cis) trans:cis trans + cis (%)

1 Benzene 44 60 48:52 73 2 Toluene 47 63 44:55 53 3 TBME 49 66 48:52 69 4 Cyclohexane 53 73 45:55 55 5 H2O 40 64 47:53 100

Given the observation by White and Shaw that electron-donating additives could increase the enantioselectivity of CoII-catalysed cyclopropanation reactions, the effect of additives was investigated.139 The most successful additives from the work by White and Shaw were chosen,139 however none gave significant improvements (Table 27).

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Table 27: Effect of additives in the asymmetric cyclopropanation optimisation using CoII(salen)-type complex 28*

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28* O EtO O EtO O (5.0 mol%) S EtO Ph Additive (5 mol%) Ph Ph N2 S S H2O, 40 ºC, 24 h (1.5 equiv) 15* 16*

Entry Additive ee ee dr Yield (trans) (cis) trans:cis trans + cis (%)

1 None 40 64 47:53 100 2 KSAc 48 63 48:52 100 3 DMSO 46 66 48:52 100

4 Br2 - - - 0

The effect of reducing the reaction temperature was investigated for the cyclopropanation on H2O and in cyclohexane (Table 28). Testing a variety of temperatures on H2O showed only very small gains in enantioselectivity over the temperature range investigated but a sharp decrease in yield was observed at 20 °C (entry 4). A sample of these temperatures were investigated using cyclohexane as the reaction solvent and again there was very little difference in the enantioselectivity of the reaction (entries 5 and 6).

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Table 28: Temperature effects on the asymmetric 28*-catalysed cyclopropanation of PVS with EDA

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28* O EtO O EtO O (5.0 mol%) S EtO Ph Solvent (0.2 M), Temperature, 24 h Ph Ph N2 S S (1.5 equiv) 15* 16*

Entry Solvent Temperature (°C) ee ee dr Yield (trans) (cis) trans:cis trans + cis (%)

1 H2O 40 40 64 47:53 100 2 H2O 30 48 65 47:53 92 3 H2O 25 51 66 47:53 92 4 H2O 20 52 77 45:55 57 5 Cyclohexane 40 53 73 45:55 55 6 Cyclohexane 25 56 74 40:60 68

Investigation into the enantioselective cyclopropanation of PVS and EDA with CoII(salen)-type complexes generated two sets of optimised conditions, both utilising enantiopure CoII(salen)-type complex 28*. These sets of conditions enabled enantioenrichments of 56% (trans) and 77% (cis) to be achieved.

2.1.4.3. Isolation and Characterisation of Single Enantiomers With the difficulties observed in achieving an asymmetric cyclopropanation, separation of the enantiomers was explored. Chiral SFC is a powerful method for the separation of chiral species into their single enantiomers and is commonly utilised for industrial applications.210 SFC is similar to HPLC, except that SFC utilises a supercritical fluid such as CO2 as an eluent and is notable for its increased speed and efficiency as well as its reduced environmental impact.210

Using chiral SFC, a sample of approximately 500 mg of trans-diastereoisomer 15 was separated into its individual enantiomers with high efficiency (1S,2R = 100% ee,

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1R,2S = 97.1% ee, see experimental section, Figure 54 for details). The same process was undertaken to achieve enantiopure samples of both enantiomers of cis-diastereoisomer 16 (1S,2S = 100% ee, 1R,2R = 99.4% ee, see experimental section, Figure 55 for details). The enantiopure sulfides were oils, however oxidation using an excess of mCPBA produced the corresponding enantiopure sulfones as crystalline solids (sulfide oxidation is covered in more detail in Section 2.3.1).

These enantiopure sulfones were analysed by single crystal X-ray diffraction to determine their absolute configurations, aided by the presence of the heavy sulfur atom (Figure 33). The crystallographic data can be found in the Cambridge Crystallographic Data Centre (CCDC), with the corresponding CCDC references given in Figure 33. The assignment of absolute configuration for each of the enantiopure sulfones was then used to assign the absolute configuration of the corresponding ancestral enantiopure sulfide.

CO2Et CO2Et (+)-77 (–)-77 Ph (1R,2S) Ph (1S,2R) S (from (+)-15) S (from (–)-15) O O O O

CCDC 1548245 CCDC 1548246

CO2Et CO2Et (–)-78 (+)-78 Ph (1S,2S) Ph (1R,2R) S (from (–)-16) S (from (+)-16) O O O O

CCDC 1550178 CCDC 1550151 Figure 33: X-ray crystal structures for enantiopure cyclopropyl sulfones with their corresponding absolute configuration and CCDC references

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Optical rotation data in the form of [�] measurements of each of the enantiopure compounds are shown in Figure 34, which allows future absolute configurational assignment of enantiopure samples of this scaffold to be made through simple optical rotation measurement.

EtO O EtO O EtO O EtO O

Ph Ph Ph Ph S S S S +57° (c = 0.257) −59° (c = 0.293) −375° (c = 0.229) +387° (c = 0.248) (1R,2S)-15 (1S,2R)-15 (1S,2S)-16 (1R,2R)-16

EtO O EtO O EtO O EtO O

Ph Ph Ph Ph S S S S O O O O O O O O

+50° (c = 0.282) −50° (c = 0.278) −38° (c = 0.250) +42° (c = 0.270) (1R,2S)-77 (1S,2R)-77 (1S,2S)-78 (1R,2R)-78 Figure 34: Specific rotation data and absolute configuration for enantiopure synthesised compounds. Optical -1 rotations were measured in CHCl3. Concentration (c) is in units of g mL

Through the use of chiral SFC, significant quantities of enantiopure bifunctional cyclopropyl scaffolds have been obtained. This could be of tremendous use in situations where the absolute configuration of the target cyclopropane-containing products is important to the biological activity or function of the compounds.

It is of importance to note that for the derivatisation of the bifunctional cyclopropyl scaffolds (Sections 2.2, 2.3 and 2.4), racemic material was used.

2.1.4.4. Conclusions In pursuit of an effective synthesis of enantiomerically-enriched scaffolds 15 and 16, an asymmetric cyclopropanation of PVS with EDA was examined, investigating a variety of CuI(BOX), CuI(PyBOX) and CoII(salen)-type complexes. Two sets of prominent conditions were developed for enantiopure CoII(salen)-type complex 28*, inducing enantioenrichments of 56% (trans) and 77% (cis). Chiral supercritical fluid chromatography enabled access to enantiopure samples of 15 and 16. X-ray

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crystallography of the corresponding sulfones allowed the absolute configuration of each isomer, and hence the absolute configuration of the precursor sulfides, to be determined. It is important to make clear that the upcoming derivatisation of the bifunctional cyclopropyl scaffolds (Sections 2.2–2.4) employed racemic material.

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2.2. Scaffold Functionalisation: Ester Derivatisation Having developed a high yielding and scalable synthesis of racemic bifunctional cyclopropyl scaffolds 15 and 16, a variety of methods were developed that allowed the functionalisation of these scaffolds by manipulation of the synthetic handles.

2.2.1. Hydrolysis Hydrolysis of the ethyl ester of cyclopropanes 15 and 16 would generate the corresponding cyclopropyl carboxylic acid compounds. Cyclopropyl carboxylic acid compounds are widely found in biologically active natural products and pharmaceutical compounds (Figure 35).211, 212 ,213 ,214

HO O HO O

H Me O Me H N 2 OH

(+)-trans-chrysanthemic acid cis-L-α-(carboxycyclopropyl)gylcine Natural product Natural product Insecticide NMDA receptor agonist

HO O HO O F

N N H N Cl Cl O O

MK-0952 UPF-648 Merck Newron Pharmaceuticals Selective PDE-4 inhibitor Kynurenine 3-hydroxylase inhibitor IC50 = 20 nM (KMO) Figure 35: Structures for selected biologically active cyclopropyl carboxylic acids. References: 211 212 213 214 (+)-trans-chrysanthemic acid, cis-L-a-(carboxycyclopropyl)glycine, MK-0952, UPF-648.

A variety of literature methods enable the hydrolysis of an ethyl ester-substituted cyclopropane to the corresponding carboxylic acid-substituted cyclopropane, with a notable example being produced by the Padwa group (Scheme 38).215 The readily available reagents and facile reaction set-up made this an attractive approach.

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O O KOH (1.0 equiv) O O H3C O H3C OH EtOH, 0 °C−rt 24 h 98% Scheme 38: Base-mediated hydrolysis of an ethyl ester-substituted cyclopropane by Padwa215

A similar set of conditions were established for the hydrolysis of 15 and 16 with very successful results. Following acidic work-up, quantitative yields of the carboxylic acids were obtained with both the trans- and the cis-diastereoisomers with no epimerisation observed in either case (Scheme 39).

O O HO O NaOH(aq) (1.1 equiv)

EtOH (0.2 M) S 30 °C, 24 h S 15 quant. 79

O O HO O NaOH(aq) (1.1 equiv)

EtOH (0.2 M) S 30 °C, 24 h S 16 quant. 80 Scheme 39: Base-mediated hydrolysis of 15 and 16 to generate carboxylic acids 79 and 80, respectively

The corresponding sodium carboxylate salt was isolated in a quantitative yield by concentrating the reaction mixture after reaching completion instead of conducting an acidic work-up (Scheme 40).

O O Na O O NaOH(aq) (1.0 equiv)

EtOH (0.2 M) S 30 °C, 24 h S 15 quant. 81

O O Na O O NaOH(aq) (1.0 equiv)

EtOH (0.2 M) S 30 °C, 24 h S 16 quant. 82 Scheme 40: Synthesis of sodium carboxylate-substituted cyclopropanes 81 and 82 from 15 and 16, respectively

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These sodium carboxylate-substituted cyclopropanes presented significant potential as cyclopropyl-building blocks. Possible transformations of the sodium carboxylate salts included amidation,216 esterification,217 and reduction.218

2.2.2. Amidation Amide bond formation utilising the ethyl ester functionality of cyclopropanes 15 and 16 would allow the divergent synthesis of a variety of amide-substituted cyclopropanes, which are important motifs in medicinal chemistry (Figure 36).219,220

Oi-Pr

H N O N NH2 O N O HN N

N Br GPR88 agonist VU0359595 cAMP regulation Phospholipidase-D antagonist EC50 = 77 nM (GPR88) Figure 36: Structures for selected biologically active amide-substituted cyclopropanes. References: GPR88 agonist.219 VU0359595.220

To test amidation conditions, the cis-cyclopropyl scaffold 16 was used due to the increased steric bulk around the ester. Benzylamine was used as the amine reactant due to its high reactivity in amidation reactions.

Initially catalytic systems were tested. Porco Jr. developed an amidation system that used 10 mol% of Zr(Ot-Bu) and was capable of utilising a broad scope of esters and amines.221 Similar conditions were tested to those optimised by Porco Jr., changing the catalyst to Zr(Oi-Pr)·HOi-Pr due to the significantly lower air and moisture sensitivity of this species (Scheme 41). The reaction failed to give any amide product and the reactant ester was recovered. This lack of reactivity may be attributed to the

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cyclopropane donating electron density into the ester p-system making it less reactive, use of a less reactive catalyst or coordination of the sulfur to the catalyst.

NH2

(1.0 equiv) H EtO O HOBt (10 mol%) N O Zr(Oi-Pr)4 ⋅HOi-Pr (10 mol%)

toluene (0.5 M), 60 °C, 4 h S S 16 83 Scheme 41: Attempted Zr(Oi-Pr)·HOi-Pr-catalysed amide bond formation

Morimoto and Ohshima reported a protocol that used La(OTf)3 as a catalyst for amide bond formation using a variety of ethyl esters, including examples that were conjugated to aromatic systems.222 When an enantioenriched chiral centre was present a to the ester carbonyl carbon, enantioenrichment was retained. Following on from this promising research, the optimised conditions were replicated using the cyclopropyl ester 16, however no reaction was observed (Scheme 42).

NH2

H EtO O (1.2 equiv) N O La(OTf)3 (5 mol%)

S 50 °C, 6 h S 16 83

Scheme 42: Attempted La(OTf)3-catalysed amide bond formation

Jamieson has shown that 20 mol% of trifluoroethanol can catalyse the amidation of a variety of methyl esters, however when an enantioenriched chiral centre was present a to the ester carbonyl carbon, almost complete racemisation was observed.223 The optimised conditions were tested with cyclopropyl ester 16 however no reaction was observed (Scheme 43).

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NH2

(1.0 equiv) H EtO O Trifluoroethanol (20 mol%) N O K3PO4 (1.0 equiv)

S THF (0.4 M), 90 °C, 22 h S 16 83 Scheme 43: Attempted trifluoroethanol-catalysed amide bond formation

Ishar has shown that Montmorillonite can act as a catalyst in microwave-assisted amidation reactions.224 Whilst only a small substrate scope was achieved by Ishar, the optimised conditions were tested on 16 for 20 minutes however no amidation product was observed (Scheme 44). The reaction was run again but with 10 equivalents of benzylamine and at 190 °C, however again no reaction was observed.

NH2

(2.5 equiv) H EtO O N O Montmorillonite K10 (300 mg)

S µW, 130 °C, 20 min S 16 83 Scheme 44: Attempted Montmorillonite-catalysed amide bond formation

Next, the cyclopropyl carboxylate was investigated with stoichiometric reagents. It has already been shown that the cyclopropyl sodium carboxylates 81 and 82 can be easily generated in a quantitative manner from esters 15 and 16, respectively (Section 2.2.1). Batey has shown that sodium carboxylates can be used directly in HBTU-mediated amide bond formation reactions.216 Due to the carboxylate of 81 and 82 having an a chiral centre there was concern over the potential for epimerisation. Low levels of epimerisation have been noted to occur by Batey for a variety of substrates.216 It has been observed that amidation using the structurally similar coupling reagent HATU results in significantly less epimerisation than the same couplings using HBTU.225 Using conditions inspired by the work by Batey,216 sodium carboxylates 81 and 82 were successfully reacted with benzylamine, morpholine, 1-methylpiperazine and 1,2,3,4-tetrahydroquinoline to produce a variety of amide substituted cyclopropanes

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(Scheme 45). Primary, secondary and anilinic amines were successful with this protocol, producing the amide-substituted cyclopropanes 83–90 in excellent yields and with no epimerisation in any examples.

R' N (1.2 equiv) R H R' HATU (1.2 equiv) Na O O N O DIPEA (3.0 equiv) R DMF (0.2 M) SPh 40 °C, 24 h SPh 81

O N H N O N O N O N O

SPh SPh SPh SPh 84 85 86 87 99% 96% 96% 94%

R' N (1.2 equiv) R H R' HATU (1.2 equiv) Na O O N O DIPEA (3.0 equiv) R DMF (0.2 M) SPh 40 °C, 24 h SPh 82

O N H N O N O N O N O

SPh SPh SPh SPh 83 88 89 90 87% 74% 90% 79% Scheme 45: HATU-mediated amide bond formation of cyclopropyl carboxylates 81 and 82

2.2.3. Reduction to an Alcohol The cyclopropylmethanol motif can be found in medicinally relevant compounds, notably in molecules belonging to the constanolactone and solandelactone families, and other structurally-similar compounds such as halicholactone (Figure 37).226,227,228

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HO OH OH

H OH O HO H H HO H O

O O H O O H

Constanolactone A Solandelactone G Halicholactone Farnesyl Protein Lipoxygenase inhibitor Transferase inhibitor Figure 37: Structures of some cyclopropylmethanol-containing natural products. References: Constanolactone A.226 Solandelactone G.227 Halicholactone.228

The cyclopropylmethanol motif could be generated from scaffolds 15 and 16 by reduction of the ethyl ester. Reductions of cyclopropyl esters typically involve the use 229,230 of a strong hydride reducing agent such as LiAlH4. This is due to the cyclopropane ring donating electron density into the ester p-system, making it less electrophilic and thus reducing its reactivity to nucleophiles. Hydride reducing agents that were less reactive than LiAlH4 were tested first however, to explore the possibilities of greater functional group tolerance.

To optimise the reduction reaction, cyclopropane 15 was tested. Initially, reduction attempts began with DIBAL in THF at –78 °C however this gave no reaction. The reactivity of DIBAL is significantly affected by the Lewis acidity of the reaction solvent.231 Therefore, the reduction was also attempted using DIBAL in cyclohexane at –78 °C however no reaction was again observed. Performing the reaction at 0 °C in THF also gave no reduction. A NaBH4/LiCl system that formed LiBH4 in situ was tested,232 however this reducing system also gave no reaction.

The failure of both DIBAL and LiBH4 systems in reducing the cyclopropyl ester of 15 was unsurprising given the widespread observation of the resistance of cyclopropyl 229,230 esters to reduction. The more commonly used reducing agent LiAlH4 was then explored. These conditions gave the primary alcohol products 91 and 92 in excellent yields and with no epimerisation (Scheme 46).

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EtO O HO LiAlH4 (2.5 equiv)

THF (0.3 M), 0–25 °C, 2 h S S 15 87% 91

EtO O HO LiAlH4 (2.5 equiv)

THF (0.3 M), 0–25 °C, 2 h S S 16 91% 92

Scheme 46: LiAlH4 reduction of cyclopropyl scaffolds 15 and 16 to form 91 and 92, respectively

2.2.4. Transesterification Cyclopropyl esters are frequently found within medicinal chemistry and biologically active compounds (Figure 38).233,234 An interesting medicinally-relevant behaviour of cyclopropyl esters is that they are more resilient to hydrolysis than simple alkyl esters due to orbital overlap between the cyclopropane ring and the ester and the electron-donating effect of the cyclopropane ring.

Me Me N Me Me N N HN O O O O O O O Me

P388 leukemia antitumour activity Nitric Oxide production inhibitor Figure 38: Examples of biologically active ester-substituted cyclopropanes. References: P388 leukemia antitumour active compound.233 NO production inhibitor.234

Given the unreactive nature of the cyclopropyl ester towards various amidation techniques, the overall transesterification process was approached instead via the cyclopropyl carboxylic acid species. Using conditions that had been developed by Bartoli and co-workers,235 cyclopropyl carboxylic acid 80 was converted to phenyl ester-substituted cyclopropane 93 in an excellent yield and with no epimerisation (Scheme 47). The success of this reaction with phenol, a relatively unreactive alcohol,

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suggested that this method would be suitable for esterification with a wide range of alcohol substrates.

PhOH (2.0 equiv) Boc O (1.0 equiv) HO O 2 PhO O MgCl2 (10 mol%)

25 °C, 15 h SPh SPh 80 74% 93 Scheme 47: Esterification of cyclopropyl carboxylic acid 80 to generate cyclopropyl ester 93

2.2.5. Conclusions The cyclopropyl ester functionality on scaffolds 15 and 16 have been derivatised selectively to form a variety of pharmaceutically-relevant motifs. The ester has been converted into carboxylic acid, sodium carboxylate salt, amide, hydroxymethyl and phenyl ester derivatives using facile and high yielding methodologies.

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2.3. Scaffold Functionalisation: Sulfide Derivatisation Derivatisation of the ethyl ester functionality of the readily available cyclopropanes 15 and 16 has been demonstrated with a range of transformations, producing a diverse variety of cyclopropane-containing compounds (Section 2.2). Next, derivatisation of the sulfide functionality of cyclopropyl scaffolds 15 and 16 was investigated. This would proceed through oxidation of the sulfide functionality, followed by exploration of a sulfoxide–metal exchange protocol as a divergent route to a wide variety of cyclopropane-containing compounds.

A concise account of this work can be found in the European Journal of Organic Chemistry (see Appendix 1).166

2.3.1. Oxidation Cyclopropyl sulfides, sulfoxides and sulfones are all important motifs within drug discovery (Figure 39).236,237,238 With the sulfide functionality on scaffolds 15 and 16 there was the possibility of accessing the corresponding sulfoxides and sulfones through oxidation reactions.

F C 3 F SO2 Me H F N O O O N CO2H S H H H S H2N S F Me S O N HO2C O O

Insecticide LY404040 γ-secretase inhibitor % Mortality at 200 ppm Glutamate receptor agonist Merck Myzus persicae = 80−100 Ki = 4.4 nM EC50 = 0.089 nM (mGlu2) Bemisia tabaci = 80−100 Ki = 0.17 nM EC50 = 1.4 nM (mGlu3) Figure 39: Structures of a biologically active cyclopropyl sulfide, sulfoxide and sulfone. References: Sulfide.236 Sulfoxide LY404040.237 Sulfone.238

The oxidation of sulfides to their corresponding sulfoxides or sulfones has been 239,240 achieved with a variety of oxidants including H2O2, meta-chloroperbenzoic acid 241 242 243 244 (mCPBA), oxone, sodium hypochlorite and O2. Each of these oxidants has their own advantages and disadvantages for their use, though of these options,

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mCPBA stood out as an attractive choice due to its crystalline solid form making it easy to handle and its low associated hazards. It is generally obtained commercially containing approximately 25% meta-chlorobenzoic acid (mCBA), however it can be easily purified through a basic potassium phosphate wash to yield pure mCPBA which can be stored for many months at 4 °C without observable levels of decomposition to mCBA occurring.

Analysis of sulfide oxidation literature led to initial conditions consisting of 2.5 equivalents of mCPBA and a reaction temperature of 25 °C being used (Scheme 48).241 These conditions were found to generate the desired cyclopropyl sulfones in quantitative yields and with complete retention of configuration.

EtO O EtO O quant. mCPBA (2.5 equiv) 94 MW = 254 CH2Cl2 (0.03 M), 25 °C, 24 h S clogP = 0.85 S O O 15

EtO O EtO O quant. mCPBA (2.5 equiv) 95 MW = 254 CH2Cl2 (0.03 M), 25 °C, 24 h S clogP = 0.85 S O O 16 Scheme 48: Oxidation of 15 and 16 to produce the corresponding sulfones 94 and 95

Next, selective oxidation to generate the corresponding sulfoxides was tackled (Table 29). Using the conditions shown in Scheme 48 but with only 1.05 equivalents of oxidant produced a near-statistical mixture of sulfur-containing species (Table 29, entries 1 and 2). A key factor in the selectivity of this reaction was temperature, and conducting the reaction at 0 °C generated the cyclopropyl sulfoxides in excellent yields with complete retention of configuration on the cyclopropane ring. Due to the generation of a new chiral centre at sulfur, diastereoisomers were generated, with sulfoxides 96 obtained in a dr of 58:42 and sulfoxides 97 obtained in a dr of 75:25 (entries 3 and 4, respectively). It is noteworthy that these oxidations were conducted on multi-gram scales, allowing large quantities of cyclopropyl sulfoxides to be generated easily.

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Table 29: Selective oxidation optimisation of cyclopropyl sulfides 15 and 16 to sulfoxides 96 and 97, respectively

EtO O EtO O EtO O EtO O mCPBA (1.05 equiv)

CH2Cl2 (0.1 M) S S S S temperature, time O O O

trans = 15 15 96 94 dr = 58:42

cis = 16 16 97 95 dr = 75:25

MW = 238 MW = 254 clogP = 0.82 clogP = 0.85

Retention of configuration

Entry Cyclopropane Temperature (°C) Yield of sulfide/sulfoxide/sulfone diastereoisomer (%) 1 trans 25 34/25/26 2 cis 25 14/39/33 3a trans 0 -/92/- 4b cis 0 -/98/- a Oxidation was conducted on 13.3 mmol of sulfide, producing 2.9 g of cyclopropyl sulfoxide product. b Oxidation was conducted on 6.7 mmol of sulfide, producing 1.6 g of cyclopropyl sulfoxide product.

2.3.2. Sulfoxide–Magnesium Exchange, Electrophilic Trap Protocol The development of a facile and high yielding CoII-catalysed cyclopropanation (Section 2.1.3.1) and the development of a high yielding and selective oxidation (Section 2.3.1) allow ready access to the topologically-different cyclopropyl sulfoxides 96 and 97. Development of a successful sulfoxide–metal exchange, electrophilic trap protocol for these cyclopropyl sulfoxides would enable a method to divergently functionalise the intact cyclopropane ring directly with a variety of electrophilic species to generate a diverse collection of cyclopropane-containing compounds.

Functional group–metal exchange reactions (also frequently called ligand-exchange reactions) are an important class of reactions that allow the interchange of a heteroatom or heteroatom-centred functional group with a metal, usually lithium or magnesium, from an organometallic species. This generates a new organometallic species that can be trapped with an electrophile. Various heteroatoms have been shown to be capable of this class of reaction including the Group 15 element phosphorus (as phosphine oxides245,246,247), Group 16 elements sulfur (as

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sulfoxides248,249,250,251 and sulfones252) and selenium (as selenoxides247), and the halides chloride,252 bromide252,253 and iodide252,253,254. The most common are iodine–metal exchange and sulfoxide–metal exchange because of the ease of incorporating the necessary heteroatom into the molecule of interest and the high reaction rates for their exchange.252

The halogen–metal exchange reaction is an equilibrium, favouring the more stable organometallic species (Scheme 49).255,256 This has been demonstrated through the analysis of the relationship between the anion orbital electronegativity of various organolithium species and the observed equilibrium constants for their exchange reactions with phenyl iodide. 255 It was found that the equilibrium is governed principally by the relative stabilities of the organolithium species on either side of the equilibrium, as highlighted by the equilibrium favouring the formation of organolithium species with greater carbanion orbital s-character and less substitution on the carbanion carbon.255

Halogen–metal exchange

X R2 X R1 R1 M R2 M Scheme 49: Equilibria for the halogen–metal exchange reaction

Qualitative rates for sulfoxide/halogen–metal exchange are in the order SO ≈ I > Br > Cl,248,257 with relative rates for iodine, bromine and chlorine–metal exchange being approximately 1011:106:1, respectively.252 Sulfoxide–metal exchange, using a p-tolylsulfinyl group, has been approximated at being slightly faster than iodine–metal exchange, however accurate rate measurement became problematic for the case of the sulfoxide–metal exchange as a result of the very rapid reaction.252 Interestingly, sulfonyl–metal exchange with a p-tolylsulfonyl group undergoes exchange at least 104 times slower than a bromide.252 Fluorine is unreactive towards halogen–metal exchange.252,258

There are three prominent possible mechanisms for halogen–metal exchange; an electron exchange (radical) mechanism, a four-centre transition state mechanism and an “ate-complex” mechanism.259 The electron transfer (radical) mechanism

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(Scheme 50) is supported by the observation of skeletal rearrangement products when alkyl bromide substrates that acted as radical probes were treated with tert-butyllithium.260,261 These observations suggested a radical mechanism being at least a minor pathway for the exchange reaction.259,260 Radicals have also been detected in exchange reaction mixtures by EPR NMR spectroscopy, though this only demonstrated that radicals may have been generated in the reaction mixture and not that they were involved in the exchange mechanism.262

Radical mechanism

R X R1 M

4-centred transition state R X

M R1

"ate-complex"

R X R1 M R X R1 M R M R1 X Scheme 50: Possible mechanisms for halogen–metal exchange

Rogers and Houk examined the initial rates of reaction between bromobenzene and n-butyllithium and found the reaction to be first order in both reactants.263 In the same work, a Hammett relationship for the reaction of substituted bromobenzenes with n-butyllithium suggested a build-up of negative charge on the aromatic ring in the transition state (r»2). Such a large r value for the reaction suggested that it did not proceed via a radical mechanism but instead either a 4-centre transition state or an “ate-complex” (Scheme 50), the latter having been initially proposed by Wittig and Schöllkopf in 1958.264 Such an “ate-complex” was isolated and characterised by Farnham and Calabrese in 1986.265 The complex was obtained by reacting pentafluorophenyllithium with pentafluorophenyl iodide at –78 °C (Scheme 51). Due to its decomposition at higher temperatures the complex was treated with tetramethylethylenediamine (TMEDA) which stabilised the hypervalent iodine salt through complexation and allowed its isolation whilst under an inert atmosphere. The sample was crystallised and X-ray crystallography performed, which showed that the

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hypervalent iodine salt possessed a near-linear geometry along the C–I–C bonds (ÐC–I–C = 175°). The isolated “ate-complex” was a competent nucleophile, delivering a C6F5 group to perfluoro-2-methyl-2-pentene in a 92% yield. This proved both that “ate-complexes” could be formed through the reaction of an organolithium and an organoiodide and that they were indeed competent nucleophiles.

F3C F F F F F 1. C6F5I (1.0 equiv) F F −78 °C F F F3C CF2CF3 F F F F I F Li F C 2. TMEDA (2.0 equiv) 3 F F F F F F F F3C CF2CF3 N N 92% Li N N

Scheme 51: Isolation and reaction of a 10-I-2 hypervalent “ate-complex” by Farnham and Calabrese265

Another important finding of this research was that the hypervalent iodine salt favoured a near-linear geometry along the C–I–C bonds,265 which was supported by the findings of Beak and Allen in their use of a combination of isotopic labelling and an endocyclic restriction system.266 A system was designed where an organolithium and an arylbromide functionality existed in the same molecule, separated by a spacer of variable length. Isotopic labelling of the bromide enabled differentiation between intramolecular and intermolecular reaction to be made. It was observed that no intramolecular bromine–lithium exchange occurred with a spacer length that generated a 6- or 8-membered endocyclic ring, suggesting that the bond angles required for successful intramolecular reaction could not be attained in these systems. Such intramolecular bromine–lithium exchange was however observed with a spacer length that generated an 18-membered endocyclic ring. The authors’ interpretation of the findings was that if a four-centre transition state mechanism was applicable then the intramolecular reactions via a 6- or 8-membered endocyclic ring should have been successful. However, due to a successful intramolecular reaction requiring a much larger endocyclic ring, it was concluded that there is a geometric requirement in the mechanism of halogen–metal exchange that the entering and leaving groups in the exchange should be close to linearity, which is what was observed in the isolated “ate-complex” by Farnham and Calabrese.265

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In conclusion, the mechanism(s) involved appear to be intricately related to the organohalide involved. Literature analysis suggests that aryl iodides,267 alkyl iodides268,269 and aryl bromides256,263,270 proceed via an “ate-complex” mechanism whereas alkyl bromides260,261,269 proceed via both “ate-complex” and radical mechanisms.

Sulfoxide–metal exchange was first discovered by Fuchs in 1929.271 Since then, sulfoxide–metal exchange has become a valuable method for both the generation of substituted sulfoxides272 and functionalised organometallic species.248 Sulfoxide–metal exchange occurs through nucleophilic attack of the reagent Grignard species at the electron-deficient sulfur, followed by expulsion of a sulfur-substituent with concomitant recovery of a tetrahedral-sulfur species (Scheme 52).273,274,275 The substituent expulsion is selective, favouring the loss of the substituent that results in the lowest energy organometallic species.275

Sulfoxide–metal exchange

O O R2 R1 S M S M R R1 R2 R Scheme 52: Equilibria for a sulfoxide–metal exchange reaction

Investigations into the mechanistic details of sulfoxide–metal exchange have supported the reaction proceeding via either a 5-coordinate oxasulfurane intermediate or a transition state involving simultaneous bond formation and bond breakage (Scheme 53).274,275,276

Oxasulfurane intermediate

R2OM S 1 R R O O R2 R1 S M S M R R1 R2 R R2OM S 1 R R Simultaneous bond formation and bond breakage Scheme 53: Sulfoxide–metal exchange mechanism via a transition state or an oxasulfurane intermediate

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Durst examined the sulfoxide–lithium exchange of various sulfoxides and claimed that the results supported an SN2 mechanism for the exchange reaction proceeding via a transition state, as opposed to via an oxasulfurane intermediate.275 This was based on the observation that sulfoxide–lithium exchange on a sulfoxide possessing two feasible leaving groups only produced one sulfoxide-containing product. However, the mechanistic explanation presumed that the energy barriers for forming the two oxasulfurane intermediates were very similar, and did not account for reversibility of the exchange reaction. Anderson and co-workers observed that treatment of p,p’-ditolylsulfoxide with p-tolyllithium produced a significant amount of p,p’-ditolyl from a coupling mechanism.274 From this it was concluded that the reaction proceeded via a 5-coordinate oxasulfurane intermediate resulting from nucleophilic attack of the organolithium into the sulfoxide sulfur. Similarly, Oae and co-workers demonstrated that both sulfoxide–metal exchange and coupling products could be generated from the same reaction of an organometallic species with a sulfoxide, indicating that in addition to the coupling mechanism, the sulfoxide–metal exchange mechanism also proceeded via an oxasulfurane intermediate.276 Furthermore, a variety of sulfuranes and oxasulfuranes have been synthesised and isolated (Figure 40).277,278

F3C CF3

C(CF ) Ph O O 3 2 Ph S S O Ph O O C(CF3)2Ph

CF F3C 3 Figure 40: Structures of a synthesised sulfurane277 and oxasulfurane278

Performing sulfoxide–metal exchange on an enantiopure sulfoxide generated the product sulfoxide with clean inversion of stereochemistry at sulfur as demonstrated by Lockard (Scheme 54).272 Mislow observed partial racemisation with sulfoxides possessing an a-proton, and explained this with an elimination–addition mechanism via the reversible formation of a methylene sulfine species (Scheme 55).273

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O S n-BuLi (1.0 equiv) O H3C S Dimethoxyethane, rt, 48 h CH3 CH3 R-configuration 26% yield S-configuration (69% recovered R-sulfoxide reactant) Scheme 54: Sulfoxide–lithium exchange giving clean inversion of stereochemistry at sulfur.272

O O O RM M S S S CH2 S H3C MH2C O MH2C

R-configuration Achiral Racemic Scheme 55: A possible racemisation pathway if the sulfoxide possesses an a-proton and the Grignard reagent is very sterically bulky.273

In the absence of factors that would dictate otherwise (e.g. conjugative orbital overlap of the intermediate organometallic species), sulfoxide–metal exchange proceeds with retention of configuration at the generated carbanion carbon. O’Brien and co-workers have demonstrated this by performing sulfoxide–magnesium exchange on a substrate possessing a stereogenic carbon a to the sulfoxide sulfur (Scheme 56).279 The substrate was diastereomerically pure and highly enantioenriched (99:1 er at sulfur). The sulfoxide–magnesium exchange generated the chiral Grignard intermediate which was then trapped with an electrophile to generate the desired product in an excellent yield and with complete enantio-retention at carbon.

i-PrMgCl Cl OMe CbO CbO CbO (2.5 equiv) (2.5 equiv) p-Tol OMe Ph S Ph MgCl Ph O THF, rt, 1 min rt, 5 min O 99:1 er 73% 99:1 er Scheme 56: Complete retention of configuration at carbon during sulfoxide–magnesium exchange.279

Sulfoxide–metal exchange followed by electrophilic trapping has been demonstrated as a powerful method to generate and utilise complex organometallic species derived from a variety of sulfoxide substrates (Scheme 57, A and B). In addition, the

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organometallic species can be trapped through transition metal-catalysed cross-coupling (Scheme 57, C and D).

A) N 1. PhMgBr (1.0 equiv) N THF, –10 °C – rt, 15 min Ph S Ph 2. O O O (1.0 equiv) O Ph O Ph 75%

B) TMS TMS 1. i-PrMgCl⋅LiCl (1.38 equiv) O THF, –50 °C OH S Cl 2. O OMe Cl Cl TMS TMS Cl (1.25 equiv) (1.0 equiv) 72%

C) OMe OMe 1. i-PrMgCl⋅LiCl (1.38 equiv) THF, 0 °C, 1 h O CO2Et S 2. ZnCl2 (1.38 equiv) Me Pd(PPh3)4 (2.5 mol%) F N CO Et F Me 2 (1.25 equiv) 85% I (1.0 equiv) THF, 25 °C, 3 h

D) PMP PMP 1. i-PrMgCl (1.5 equiv) N N THF, –78 – 0 °C H3C Ph H C Ph 3 H p-Tol S H 2. O F Br

(2.0 equiv) F Pd (dba) ⋅CHCl (2.5 mol%) 2 3 3 70% (t-Bu)3P (5.5 mol%) ZnCl2 (1.5 equiv) THF, rt, 15 h Scheme 57: Examples of sulfoxide–metal exchange followed by either trapping with an electrophile or transition metal-catalysed cross-coupling. References: A280, B281, C248, D282

Sulfoxide–metal exchange and halogen–metal exchange have been performed on cyclopropanes, demonstrating both trapping of the cyclopropyl organometallic species with electrophiles and transition metal-catalysed cross-coupling (Scheme 58).

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A) 1) i-PrMgCl (1.1 equiv) Et2O/CH2Cl2 Me −50 °C, 10 min Me NC S Ph 2) NC O Br (1.3 equiv) 41% over 4 steps 73% CuCN⋅2LiCl (0.5 mol%) −50 °C - rt

B) 1) n-BuLi (3.0 equiv) 1) n-BuLi (2.0 equiv) Ph THF/hexane toluene i-Pr i-Pr S O −80 °C - −20 °C, 1 h −80 °C, 1 h i-Pr 2) S O 2) H O (3.0 equiv) S O Br 2 H Ph Ph −80 °C - 0 °C 3 steps to synthesise 60% 70% (5.0 equiv) −80 °C to 0 °C

C) 1) i-PrMgCl ( 1.3 equiv) EtO O EtO O ZnBr2 (1.3 equiv) THF, −80 °C - rt, 15 min

2) I I CO2Me (1.2 equiv) MeO2C 92% 31% over 5 steps (1.0 equiv)

Pd(dba)2 (5.0 mol%) tri(2-furyl)phosphine (10 mol%) THF, rt, 6 h Scheme 58: Examples of cyclopropyl sulfoxide/halogen–metal exchange reactions. References: A250, B283, C284

Knochel and co-workers demonstrated sulfoxide–magnesium exchange followed by transmetalation to copper before trapping the cyclopropyl organometallic species with methallyl bromide, generating the tetrasubstituted cyclopropane in an excellent yield (Scheme 58A).250 Two consecutive sulfoxide–lithium exchange, electrophilic trap protocols have been demonstrated on a single cyclopropane ring by Marek and co-workers, with the resulting cyclopropyl lithium intermediates being trapped with 283 benzyl bromide and a proton from H2O (Scheme 58B). Iodine–magnesium exchange on a cyclopropane ring has been demonstrated by Knochel with a cis-substituted cyclopropane ring also bearing an ethyl ester functionality (Scheme 58C).284 The cis-oriented ester reportedly stabilised the cyclopropyl Grignard intermediate by both chelation and inductive effects. There were no comments on observations of Grignard attack into the ester carbonyl, suggesting chemoselectivity for the iodide, which was an important factor during the design of the target bifunctional

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cyclopropyl scaffold for the work presented in this thesis. The observation that a cyclopropyl ester was unaffected by halogen–magnesium exchange conditions meant that sulfoxide/halogen–magnesium exchange and ester functionalisation offered the possibility of orthogonal and divergent functionalisation pathways for a bifunctional cyclopropyl scaffold. Whilst examples of cyclopropanes possessing an exchangeable functionality and additional compatible functionality exist (Scheme 58), they often require a relatively lengthy synthesis for use as an initial scaffold. In contrast, cyclopropanes 96 and 97 bearing ester and sulfoxide functionality have been shown to be readily accessed in 2 synthetic steps (Sections 2.1.3.1 and 2.3.1).

With a facile route to bifunctional cyclopropyl sulfoxides 96 and 97, the development of a robust and reliable sulfoxide–metal exchange, electrophilic trap protocol which would enable divergent functionalisation of the intact cyclopropane ring commenced. In the sulfoxide–magnesium exchange of cyclopropyl sulfoxide 96 with an alkyl organometallic reagent the exchange reaction has two potential exchange pathways by which it can proceed (Scheme 59). The prevalence of each pathway is dictated by the stability of the organometallic species it produces, indicated by its pKaH, with the generation of the organometallic species possessing the lowest pKaH value being favoured. i-PrMgCl is a representative alkyl organometallic reagent commonly used 285 for sulfoxide/halogen–magnesium exchange reactions and possesses a pKaH of 51.

EtO O MgCl

S O pKaH = 43 98

EtO O Pathway 1 MgCl S

O pKaH = 51 Pathway 2 96

EtO O O S

MgCl 99 100 Scheme 59: Potential reaction pathways for the sulfoxide–magnesium exchange of 96

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Provided that at least one of the sulfoxide substituents generates a product organometallic species with a pKaH below 51 it is reasonable to assume that the sulfoxide–magnesium exchange may proceed on thermodynamic grounds. If this was not the case then no exchange reaction would be expected. In a scenario where the two sulfoxide substituents generated organometallic products with similar pKaH values then both pathways may be utilised to a significant extent, producing a mixture of products. For the sulfoxide–magnesium exchange of cyclopropyl sulfoxide 96, the 286 phenyl anion produced from Pathway 1 possesses a pKaH of 43, however the pKaH of the ester-substituted cyclopropyl anion 99 produced by Pathway 2 is unknown. The 285,287,288 pKaH of cyclopropane however is 46, and the presence of the electron-withdrawing ester would act to reduce that significantly. From the observation made by Knochel and co-workers (Scheme 58A) that a sulfoxide possessing a phenyl ring and a nitrile-substituted cyclopropane underwent clean sulfoxide–magnesium exchange with i-PrMgCl to generate the cyclopropyl Grignard species, it appeared likely that sulfoxide–magnesium exchange on 96 would also result in the selective generation of a cyclopropyl Grignard species.250

2.3.2.1. Reaction Optimisation Initial optimisation of the sulfoxide–metal exchange reaction began on the trans-cyclopropyl sulfoxide 96. Knochel has previously described how the cyclopropyl organometallic species that would originate from cis-cyclopropyl sulfoxide 97 could benefit from stabilisation as a result of metal chelation by the ester,284 therefore trans-cyclopropyl sulfoxide 96 was used for the optimisation, where such chelating stabilisation was not possible. After analysis of the literature on sulfoxide/iodine–metal exchange, an initial set of conditions were selected (Scheme 60).

i-PrMgCl (1.5 equiv) EtO O THF, – 78 °C Electrophile EtO O O EtO O O 10 min (1.5 equiv) S S S MgCl O E 96 99 100 100 Scheme 60: Initial sulfoxide–magnesium exchange conditions for cyclopropyl sulfoxide 96

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The success of the reaction would be analysed by the yields of the products obtained; the yield of iso-propyl phenyl sulfoxide 100 indicated the success of the sulfoxide–magnesium exchange and the yield of the trapped cyclopropane indicated the success of the electrophilic trapping of the cyclopropyl Grignard intermediate. As such, during early optimisation a variety of electrophiles were tested whilst varying reaction conditions to try to find a competent electrophile whilst investigating reaction parameters.

The concentrations of the organometallic reagents used in the sulfoxide–metal exchange optimisation were regularly and frequently determined throughout the period of their use. This ensured the correct amount of reagent was being added. The organometallic reagent concentration was determined by titration with salicylaldehyde phenylhydrazone as developed by Love and Jones,289 with two colour changes observed; colourless to yellow and yellow to red (Scheme 61). The concentration was calculated using the volume of organometallic reagent added for the solution to just turn a persistent orange colour.

H H N RM N RM N N N N

OH O O Salicylaldehyde (yellow) (red) phenylhydrazone Scheme 61: Organometallic reagent titration using salicylaldehyde phenylhydrazone, as initially developed by Love and Jones289

The initial conditions involved the addition of a solution of i-PrMgCl (0.32 mL, 1.87 M in THF, 1.5 equiv) to a –78 °C solution of the cyclopropyl sulfoxide (95 mg, 1.0 equiv) in THF (4.0 mL, 0.1 M), followed by the addition of 4,4’-dimethylbenzophenone as the electrophilic trap (Table 30). The reaction was successful, giving a 41% yield of the trapped cyclopropane 101 and a quantitative yield of iso-propyl phenyl sulfoxide (Table 30, entry 1). The reaction also proceeded with complete retention of configuration at the cyclopropyl carbon. The same conditions were used with EtMgCl as the Grignard reagent, however this produced inferior results, as indicated by the lower yield of alkyl phenyl sulfoxide by-product (entries 1 and 2). Interestingly, a higher

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yield of trapped cyclopropane 101 was observed with EtMgCl. Knochel has shown that the presence of inorganic salts, particularly LiCl, can improve certain reactions involving organometallic species,290 however using i-PrMgCl·LiCl in the reaction showed a significant decrease in the yield of the trapped cyclopropane 101 (entry 3). No remaining reactant sulfoxide 96 and no side-products resulting from electrophilic attack of a Grignard species into the cyclopropyl ester were observed for any of these reactions (Table 30, entries 1–3).

Table 30: Effect of Grignard reagent on the sulfoxide–magnesium exchange of 96

EtO O EtO O 1) RMgCl (1.5 equiv) O R OH THF, –78 °C, 10 min OH S p-tol p-tol Ph R Ph S 2) O p-tol O p-tol p-tol p-tol 96 101 102 103 (1.5 equiv) THF, –78 °C–rt, 1 h

Entry RMgCl Yield of Yield of Yield of 101 (%) 102 (%) 103 (%)

1 i-PrMgCl 41 100 17 2 EtMgCl 51 88 13 3 i-PrMgCl·LiCl 23 100 12 Yields determined by 1H NMR spectroscopy with comparison to internal standard (dibenzyl ether).

Next, the order of addition for the sulfoxide–magnesium exchange was investigated

(Table 31). The electrophile was changed to benzophenone, as the CH3 groups on 4,4’-dimethylbenzophenone and the related by-products generated a complex 1H NMR spectrum for the unpurified material, which made accurate yields difficult to determine. Additionally, removing the +I inductive effects of the methyl substituents would make the electrophile slightly more electrophilic, improving the trapping of the cyclopropyl Grignard intermediate. The equivalents of the electrophile were also increased from 1.5 to 2.0 and the exchange temperature was kept at –78 °C for the 1 h electrophilic trapping time.

The addition of i-PrMgCl to a solution of the sulfoxide gave slightly higher yields of the trapped cyclopropane 104 and of the sulfoxide by-product 100 than addition of a solution of the sulfoxide to i-PrMgCl (Table 31).

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Table 31: Effect of addition order on the sulfoxide–magnesium exchange of 96

EtO O EtO O 1) i-PrMgCl (1.5 equiv) THF, –78 °C, 10 min O OH S Ph Ph S 2) O Ph O Ph 96 Ph Ph 104 100 (2.0 equiv) THF, –78 °C, 1 h

Entry Addition Yield of Yield of 104 (%) 100 (%)

1 i-PrMgCl to R2SO 25 100 2 R2SO to i-PrMgCl 14 89 Yields determined by 1H NMR spectroscopy with comparison to internal standard (dibenzyl ether).

The yield of trapped cyclopropane-containing product was still low despite achieving a high yield of iso-propyl phenyl sulfoxide by-product. This indicated that the electrophile was still not very reactive with the cyclopropyl Grignard intermediate being formed. Benzaldehyde was therefore tested, due to its highly electrophilic nature, however it too gave a low yield of the trapped cyclopropane-containing product (Table 32, entry 1). In order to potentially increase the reactivity of the reaction it would be possible to perform a sulfoxide–lithium exchange and form a cyclopropyl organolithium intermediate. However, the presence of organolithium species in the reaction mixture could have significant detrimental effects due to undesirable side reactions such as electrophilic attack into the cyclopropyl ester. The reaction was repeated using n-BuLi however this generated an extremely complex reaction mixture with no signs of cyclopropane-containing material by 1H NMR spectroscopy (Table 32, entry 2).

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Table 32: Effect of performing sulfoxide–magnesium exchange and sulfoxide–lithium exchange on 96

EtO O EtO O 1) RM (1.5 equiv) THF, –78 °C, 10 min O OH Ph S S 2) O Ph R Ph O H Ph H 96 105 102 (2.0 equiv) THF, –78 °C, 1 h

Entry RM Recovered 96 Yield of Yield of (equiv) 105 (%) 102 (%) 1 i-PrMgCl 0.13 25 76 2 n-BuLi 0.00 - 20 Yields determined by 1H NMR spectroscopy with comparison to internal standard (dibenzyl ether).

With a low yield of trapped cyclopropane still being obtained, I2 was tested as an electrophile given its weak I–I s-bond. This produced an excellent 82% yield of trapped iodocyclopropane 106 with complete retention of configuration at the cyclopropyl carbon, along with an almost quantitative yield of the sulfoxide by-product 100

(Scheme 62). The sulfoxide–magnesium exchange, I2 trap was also carried out using cis-cyclopropyl sulfoxide 97, generating the corresponding cis-cyclopropyl iodide 107 in a good yield of 58% with complete retention of configuration at the cyclopropyl carbon. Analysis of the 1H NMR spectrum from the unpurified reaction mixture of 107 indicated that significantly more product was synthesised, however some was lost upon purification due to its volatility.

EtO O 1) i-PrMgCl (1.5 equiv) EtO O THF, –78 °C, 10 min O S Ph Ph S 2) I2 (2.0 equiv) O THF, –78 °C, 1 h I 96 82% 94% 106 100

Scheme 62: Sulfoxide–magnesium exchange of 96 followed by electrophilic trapping with I2

The consistently high yield of iso-propyl phenyl sulfoxide 100 obtained from the sulfoxide–magnesium exchange conditions and the finding that I2 acted as an effective electrophile to give good yields of the trapped cyclopropane 106 enabled investigation into the stability of the cyclopropyl Grignard intermediate. Using this yield of 82% of

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iodocyclopropane 106 as a starting point to investigate the stability of the cyclopropyl Grignard intermediate, there was sufficient yield margin to confidently observe both trends of decreasing yields caused by a reaction variable promoting degradation of the cyclopropyl Grignard intermediate and trends of increasing yields due to a reaction variable promoting the electrophilic trapping.

2.3.2.2. Stability Investigations into Cyclopropyl-MgCl Intermediate As mentioned briefly previously, Knochel demonstrated that organometallic species can have their stability and reactivity increased by the presence of inorganic salts, particularly LiCl, for certain reactions.290 This was tested previously (Table 30, entry 3), where using i-PrMgCl·LiCl resulted in an excellent yield of the by-product sulfoxide but a significantly decreased yield of the trapped cyclopropane product. In the context of Knochel’s work, this could potentially be explained by the cyclopropyl Grignard that was formed by i-PrMgCl·LiCl being more stable and therefore less reactive under the reaction conditions. If this were the situation, it may be the case that the presence of LiCl in the reaction mixture results in a slower rate of electrophilic trapping but a higher overall yield due to the increased stability of the intermediate if given enough time to react. To examine the effects, if any, of the presence of LiCl on the stability of the cyclopropyl Grignard intermediate over time, the sulfoxide–magnesium exchange was conducted with either i-PrMgCl or i-PrMgCl·LiCl and the I2 electrophilic trap added after various time periods after Grignard reagent addition, ranging from immediately afterwards to two hours later. Each of the reaction mixtures were worked-up and the yield of iodocyclopropane 106 calculated through analysis of the 1H NMR spectrum by comparison with a known amount of added dibenzyl ether as an internal standard. The results are plotted in Graph 1, with each data point representing an individual reaction.

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EtO O Grignard reagent EtO O EtO O (1.5 equiv) I2 (2.0 equiv) Ph S THF, −78 °C THF, −78 °C, 1 h O exchange time M I 96 106 100 90 80 70 60 50 40 30 20

Yield0of0iodocyclopropane0(%) 10 0 0 20 40 60 80 100 120 Sulfoxide?magnesium0exchange0time0(min) ii?PrMgCl.LiCl· ii?PrMgCl

Graph 1: The effect of LiCl and sulfoxide–magnesium exchange time on the yield of 106. Yields determined by 1H NMR spectroscopy with comparison to internal standard (dibenzyl ether).

It can be seen from Graph 1 that the addition of LiCl makes essentially no observable difference to the reaction, with the yields at each time period being almost identical for i-PrMgCl and i-PrMgCl·LiCl. Given that i-PrMgCl is much less expensive than i-PrMgCl·LiCl, the sulfoxide–magnesium exchange protocol continued to use i-PrMgCl for the remaining reaction optimisation and scope. It can also be seen from Graph 1 that the sulfoxide–magnesium exchange was complete after 10 minutes at –78 °C, meaning that any greater amount of time was not of benefit. Finally, Graph 1 illustrates that the cyclopropyl Grignard intermediate was stable at –78 °C for at least 2 hours with no degradation, as can be seen from the constant yield of 106 between exchange times of 10 minutes and 2 hours. Presented with its impressive stability at –78 °C, the thermal stability of the cyclopropyl Grignard intermediate 99 was investigated over a range of temperatures (Graph 2).

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EtO O EtO O 1) temperature EtO O i-PrMgCl (1.5 equiv) incubation time Ph S THF, −78 °C 2) I2 (2.0 equiv) O 10 min MgCl THF, 1 h I 96 99 106

100 90 80 70 60 50 40 30 20

Yield0of0iodocyclopropane0(%) 10 0 0 20 40 60 80 100 120 Incubation0time0(min) T0=0−300°C T0=000°C T0=0250°C

Graph 2: Investigation into the thermal stability of the cyclopropyl Grignard species derived from 96. Yields determined by 1H NMR spectroscopy with comparison to internal standard (dibenzyl ether).

The sulfoxide–magnesium exchange was conducted at –78 °C for 10 minutes, then the reaction mixture was warmed to either –30 °C, 0 °C or 25 °C and kept at this incubation temperature for between 10 minutes and 2 hours. After this time, I2 was added to trap the remaining cyclopropyl Grignard intermediate, with the reaction being left for 1 hour at the incubation temperature to allow this to occur. The results from this investigation which are displayed in Graph 2 show that there was complete stability of cyclopropyl Grignard intermediate 99 at –30 °C and 0 °C for up to 2 hours, however there was significant degradation at 25 °C. At 25 °C there was an approximate 50% decrease in yield between the data points corresponding to incubation for 10 minutes and 1 hour, and around a 67% decrease between incubation for 10 minutes and 2 hours. There were no clearly identified products formed from the decomposition of the cyclopropyl Grignard intermediate. This demonstrated that to achieve the maximum reactivity of the cyclopropyl Grignard intermediate whilst ensuring its complete stability, 0 °C was the optimum temperature to conduct the electrophilic trapping.

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With the stability of the cyclopropyl Grignard intermediate now well understood, the resulting optimised conditions were to be tested with a wide variety of electrophiles to generate a diverse collection of cyclopropane-containing compounds.

2.3.2.3. Electrophile Scope for trans-Cyclopropyl Scaffold With the optimised sulfoxide–magnesium exchange, electrophilic trap conditions proven to be successful with both trans- and cis-cyclopropyl sulfoxide diastereoisomers 96 and 97, the electrophile scope was explored (Schemes 63 and 64 respectively). First, the electrophile scope for trans-cyclopropyl sulfoxide 96 is described, with the ethyl ester abbreviated to CO2Et for conciseness (Scheme 63). The synthesised cyclopropane-containing compounds are shown along with a variety of their physicochemical properties, namely, molecular weight, lipophilicity (AlogP, calculated by LLAMA software),291 number of hydrogen bond donors and acceptors, fraction of sp3 centres and the polar surface area of the compound.

CO Et 2 1) i-PrMgCl (1.5 equiv) CO Et THF, -78 ºC, 10 min 2 Ph S 2) Electrophile (2.0 equiv) E O THF, 0 ºC 96 106, 108–119

Entry Electrophile Product

CO Et MW = 212 O 2 71% AlogP = 1.91 a HBD/HBA = 1/3 1 H dr = 56:44 108 Fsp3 = 0.92 OH PSA = 46.53 Å2

M = 220 O CO2Et W 94% AlogP = 2.09 a 2 H dr = 61:39 HBD/HBA = 1/3 109 Fsp3 = 0.46 OH PSA = 46.53 Å2

M = 221 O CO2Et W 90% AlogP = 1.08 a 3 H N dr = 52:48 HBD/HBA = 1/4 110 Fsp3 = 0.50 N OH PSA = 59.42 Å2

CO2Et MW = 186 O AlogP = –0.16 66% 4a OH HBD/HBA = 1/4 111 Fsp3 = 0.89 O 2 O PSA = 55.76 Å

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CO2Et M = 365 O OH W AlogP = 5.05 80% 5b HBD/HBA = 1/3 Cl 112 Fsp3 = 0.32 Cl Cl PSA = 46.53 Å2

CO2Et M = 298 O W OH AlogP = 1.98 90% 6b HBD/HBA = 1/5 113 Fsp3 = 0.35 N N N N PSA = 72.31 Å2

M = 218 O CO2Et W AlogP = 2.19 38% 7b HBD/HBA = 0/3 Cl 114 Fsp3 = 0.38 O PSA = 43.37 Å2

O CO2Et MW = 233 C AlogP = 1.81 H 75% 8c HBD/HBA = 1/4 N N 115 Fsp3 = 0.38 O PSA = 55.40 Å2

OMe MW = 252 CO2Et AlogP = 3.53 OMe 55% 9c S HBD/HBA = 0/3 S 116 Fsp3 = 0.46 S MeO PSA = 35.53 Å2

MW = 240 CO2Et AlogP = 2.07 82% 10a,d I HBD/HBA = 0/2 2 106 Fsp3 = 0.83 I PSA = 26.30 Å2

CO Et 2 MW = 240 i-PrO O AlogP = 3.10 B 54% 11c O HBD/HBA = 0/4 O B 117 Fsp3 = 0.92 O PSA = 44.76 Å2

MW = 276 CO2Et AlogP = 2.77 c 43% 12 Cl Si(OEt)3 HBD/HBA = 0/5 118 3 Si(OEt) Fsp = 0.92 3 PSA = 53.99 Å2

M = 142 CO2Et W O AlogP = 0.47 85% 13c HBD/HBA = 0/3 N H H 119 Fsp3 = 0.71 O PSA = 43.37 Å2 Scheme 63: Electrophile scope for the sulfoxide–magnesium exchange, electrophilic trapping of 96. a Trapping time = 1 h. b Trapping time = 3 h. c Trapping time = 6 h. d Electrophilic trapping conducted at –78 °C.

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The trans-Grignard intermediate derived from trans-cyclopropyl sulfoxide 96 was trapped effectively with aliphatic-, aryl- and heteroaryl-substituted aldehydes, giving excellent yields of the resulting trans-cyclopropane products 108–110 (Scheme 63, entries 1–3). The physicochemical properties of these compounds fit well within fragment guidelines and possess functionality that can act as potential pharmacophores or synthetic vectors for further manipulations. Dialkyl, diaryl and diheteroaryl ketones were also competent electrophiles, giving good to excellent yields of the product cyclopropanes 111–113 (entries 4–6). Due to the large rate difference between sulfoxide–magnesium exchange and chlorine–magnesium exchange the aryl chloride functionality in entry 5 remained untouched, with no products observed from chlorine–magnesium exchange. This left the aryl chloride functionalities as possible synthetic vectors for further derivatisation. These ketone-derived cyclopropane-containing products fitted well into fragment or lead-like chemical space. Acyl chlorides could be used to trap the cyclopropyl Grignard intermediate, giving a reasonable yield of the cyclopropyl ketone 114 (entry 7). This occurred without the need to transmetalate the cyclopropyl Grignard to copper, which is often required to efficiently react a Grignard species with an acyl chloride.284,292 Such transmetalations generally use CuCN, which is potentially extremely dangerous due to the risk of hydrogen cyanide evolution. Phenyl isocyanate was an effective electrophile, generating cyclopropyl amide 115 in an excellent yield (entry 8), and trapping with a disulfide produced the cyclopropyl sulfide 116 in a good yield (entry 9). Having generated a range of cyclopropane-containing fragments and lead-like compounds through the sulfoxide–magnesium exchange, electrophilic trap protocol, the utilisation of this methodology towards synthesising cyclopropyl building blocks was explored.

As shown in the reaction optimisation, I2 was an effective trap which generated cyclopropyl iodide 106 in an excellent yield (entry 10). Trapping with an iso-propoxy dioxaborolane generated the corresponding cyclopropyl boronic ester 117 in a good yield (entry 11), and trapping with a silyl chloride generated the corresponding cyclopropyl silane 118 (entry 12). Cyclopropane-containing products 106, 107 and 108 could be taken forward for further derivatisation through cross-coupling of the installed functionality, with methods for these transformations having been developed for similar cyclopropanes.293,294,295 Finally, trapping with N,N-dimethylformamide

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generated cyclopropyl aldehyde 119 in an excellent yield (entry 13), which could be used as a building block in derivatisation reactions such as reductive amination.296

2.3.2.4. Electrophile Scope for cis-Cyclopropyl Scaffold A similar electrophile scope was achieved with the cis-Grignard intermediate derived from cis-cyclopropyl sulfoxide 97 (Scheme 64). Aliphatic-, aryl- and heteroaryl-substituted aldehydes were successful electrophiles, giving good to excellent yields of the resulting cis-cyclopropane products 120–122 which fit within fragment guidelines (Scheme 64, entries 1–3). The more electron-rich aldehydes (entries 1 and 2) resulted in lactonisation after the initial electrophilic trapping, producing the corresponding bicyclic product. The observed electronic-dependence of the lactonisation was due to the more electron-rich oxyanions being more reactive towards the proximal ester carbonyl. Dialkyl, diaryl and diheteroaryl ketones were also successful, generating 123–126 (entries 4–6). Similar to when trapping with aldehydes, lactonisation was observed with certain ketone substrates. Phenyl acyl chloride was compatible, giving a good yield of the cis-cyclopropyl ketone 127 (entry 7). Finally, cis-cyclopropyl iodide 107 and cis-cyclopropyl boronic ester 128 building blocks were synthesised in good to excellent yields (entries 8 and 9).

CO Et 2 1) i-PrMgCl (1.5 equiv) CO Et THF, -78 ºC, 10 min 2 Ph S 2) Electrophile (2.0 equiv) E O THF, 0 ºC 97 107, 120–128

Entry Electrophile Product

O MW = 166 O O 86% AlogP = 2.04 a HBD/HBA = 0/2 1 H dr = 61:39 120 Fsp3 = 0.90 PSA = 26.30 Å2

O M = 174 O W O 69% AlogP = 1.90 a 2 H dr = 56:44 HBD/HBA = 0/2 121 Fsp3 = 0.36 PSA = 26.30 Å2

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M = 221 O CO2Et W 86% AlogP = 1.08 a 3 H N dr = 57:43 HBD/HBA = 1/4 122 Fsp3 = 0.50 N OH PSA = 59.42 Å2

O MW = 154 AlogP = 2.25 O O 49% 4b HBD/HBA = 0/2 123 Fsp3 = 0.89 PSA = 26.30 Å2

O M = 319 O O W AlogP = 5.05 Cl 65% 5b HBD/HBA = 0/2 124 Fsp3 = 0.24 Cl Cl PSA = 26.30 Å2

CO2Et M = 298 O W OH 43% AlogP = 1.98 6b 125 HBD/HBA = 1/5 ( 15% lactone 126) 3 N N N + Fsp = 0.35 N PSA = 72.31 Å2

O CO2Et MW = 218 AlogP = 2.19 64% 7b Cl 127 HBD/HBA = 0/3 Fsp3 = 0.38 O PSA = 43.37 Å2

MW = 240 CO2Et AlogP = 2.07 a,d 58% 8 I2 HBD/HBA = 0/2 107 3 I Fsp = 0.83 PSA = 26.30 Å2

CO2Et MW = 240 i-PrO O B AlogP = 3.10 c O 82% 9 O B HBD/HBA = 0/4 128 3 O Fsp = 0.92 2 PSA = 44.76 Å Scheme 64: Electrophile scope for the sulfoxide–magnesium exchange, electrophilic trapping of 97. a Trapping time = 1 h. b Trapping time = 3 h. c Trapping time = 6 h. d Electrophilic trapping conducted at 0 °C.

Having demonstrated a wide electrophile scope for the sulfoxide–magnesium exchange, electrophilic trap protocol with both the trans- and cis-cyclopropyl sulfoxides and generating a variety of cyclopropane-containing fragments, lead-like compounds and building blocks in the process, investigation into the utilisation of the

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trans- and cis-cyclopropyl Grignard intermediates for cross-coupling methodology began.

2.3.3. Sulfoxide–Magnesium Exchange, Negishi Cross-Coupling Protocol (Hetero)aryl-substituted cyclopropanes are of huge importance to medicinal chemistry297 and are found within a large number of pharmaceutical drugs (Figure 41).

HO O

F S OH O N N H O N N NH HO N N N N H OH F O N

O O F

MK-0952 Ticagrelor Merck AstraZeneca Bristol-Myers Squibb Selective PDE-4 inhibitor Platelet aggregation inhibitor Oral melatonin receptor agonist

Oi-Pr

NH2 N O N S O O N

NC NH N

BMS-505130 Cipralisant Bristol-Myers Squibb Merck GPR88 agonist Selective serotonin Histamine H3-antagonist cAMP regulation reuptake inhibitor Ki = 0.18 nM (SERT) EC50 = 77 nM (GPR88) Figure 41: Examples of medicinally important (hetero)aryl-substituted cyclopropanes. References: MK-0952.213 Ticagrelor.298 Oral melatonin receptor agonist.299 BMS-505130.300 Cipralisant.301 GPR88 agonist.219

With a powerful sulfoxide–magnesium exchange protocol in hand, it was a possibility to build upon that with cross-coupling methodology to allow aromatic and heteroaromatic rings to be installed directly onto the intact cyclopropane ring. Knochel has reported examples of halogen–magnesium exchange, Negishi cross-coupling on

159

cyclopropane rings however only a very limited scope of aromatic halides was achieved.284,292

In 2013 the Bull group developed methodology for a sulfoxide–magnesium exchange, Negishi cross-coupling protocol on aziridines which allowed the installation of a variety of substituted phenyl rings from the corresponding bromobenzenes (Scheme 65).282

PMP PMP 1. i-PrMgCl (1.5 equiv) N R = H 80% N THF, –78 – 0 °C H3C Ph R = p-Me 70% H3C Ph H R = p-F 70% p-Tol S H 2. R = p-Cl 65% O Br R = o-OMe 81% R R (2.0 equiv)

Pd2(dba)3⋅CHCl3 (2.5 mol%) (t-Bu)3P (5.5 mol%) ZnCl2 (1.5 equiv) THF, rt, 15 h Scheme 65: Sulfoxide–magnesium exchange, Negishi cross-coupling on an aziridine282

It was envisaged that combining the optimised set of sulfoxide–magnesium exchange conditions developed for the ester-substituted cyclopropyl sulfoxides 96 and 97 with a suitable set of Negishi cross-coupling conditions would enable direct functionalisation of the intact cyclopropane with (hetero)aromatic rings. With this in mind, it seemed reasonable that the Negishi cross-coupling conditions developed within the Bull group282 for aziridinyl Grignards could be applied to cyclopropyl Grignards, functioning as a starting point from which optimisation could be conducted if necessary.

Given the known instability of the ester-substituted cyclopropyl Grignard species 99 at 25 °C, the Negishi cross-coupling protocol was adapted to allow transmetalation to zinc to occur at 0 °C over 1 hour before warming the reaction mixture to 25 °C for the Negishi cross-coupling to take place. These conditions proved to be very successful in the cross-coupling of bromobenzene with either trans- or cis-cyclopropyl sulfoxides 96 and 97, giving the corresponding aryl-substituted cyclopropane 129 or 130 in an excellent yield with complete retention of configuration at the cyclopropyl carbon (Scheme 66). With the success of the sulfoxide–magnesium exchange, Negishi cross-coupling protocol determined, a variety or aromatic and heteroaromatic

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bromides were tested. The electron-poor 4-chlorobromobenzene gave an excellent yield of 131, with no reaction observed at the aryl chloride, leaving the functional handle intact for further elaboration. Also, the electron-rich 4-bromoanisole gave an excellent yield of 132. b-Bromostyrene gave an excellent yield of the vinyl cyclopropane 133. Next, the cross-coupling of heteroaromatics onto the intact cyclopropane ring was investigated. 2-Bromopyridine and 2-bromopyrimidine gave good yields of the pyridine- and pyrimidine-substituted cyclopropanes 134 and 135 as fragments possessing low lipophilicities. Finally, a 3-bromoindole was successful, producing the indole-substituted cyclopropane 136 in a 94% yield as a potential lead-like compound.

EtO O 1. i-PrMgCl (1.5 equiv) Addition time = 10 s, EtO O THF, -78 ºC, 10 min Ph S 2. Pd2(dba)3 (2.5 mol%) (Het)Ar O (t-Bu)3P (5.5 mol%) 96 ZnCl2 (1.5 equiv) 129–136 THF, 0 ºC, 1 h 3. (Het)ArBr (2.0 equiv) THF, 25 ºC, 15 h

EtO O EtO O EtO O EtO O

Cl OMe From the cis-cyclopropane 97 74% 76% 85% 73% 129 130 131 132 MW = 190 MW = 190 MW = 225 MW = 220 AlogP = 2.95 AlogP = 2.95 AlogP = 3.45 AlogP = 3.20 HBD/HBA = 0/2 HBD/HBA = 0/2 HBD/HBA = 0/2 HBD/HBA = 0/3 Fsp3 = 0.42 Fsp3 = 0.42 Fsp3 = 0.42 Fsp3 = 0.46 PSA = 26.30 Å2 PSA = 26.30 Å2 PSA = 26.30 Å2 PSA = 35.53 Å2

EtO O EtO O EtO O EtO O

N N Boc N N

84% 60% 59% 94% 133 134 135 136 MW = 216 MW = 191 MW = 192 MW = 329 AlogP = 3.81 AlogP = 1.31 AlogP = 0.56 AlogP = 4.39 HBD/HBA = 0/2 HBD/HBA = 0/3 HBD/HBA = 0/4 HBD/HBA = 0/5 Fsp3 = 0.36 Fsp3 = 0.46 Fsp3 = 0.50 Fsp3 = 0.47 PSA = 26.30 Å2 PSA = 39.19 Å2 PSA = 52.08 Å2 PSA = 57.53 Å2 Scheme 66: Scope of (hetero)aryl bromides for the sulfoxide–magnesium exchange, Negishi cross-coupling

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The high yields and broad (hetero)aryl bromide scope achieved show that the sulfoxide–magnesium exchange, Negishi cross-coupling protocol developed for cyclopropanes 96 and 97 is a powerful way to generate (hetero)aryl-substituted cyclopropanes in a divergent manner.

2.3.4. Conclusions A sulfoxide–magnesium exchange, electrophilic trap protocol has been developed for cyclopropyl sulfoxides 96 and 97 that allows chemoselective generation and reaction of the cyclopropyl Grignard whilst leaving the cyclopropyl ester functionality intact. The stability of the trans-cyclopropyl Grignard intermediate 99 originating from trans-cyclopropyl sulfoxide 96 was investigated. The trans-cyclopropyl Grignard intermediate 99 was stable at –30 °C and 0 °C but underwent gradual decomposition at 25 °C. To maximise the reactivity of 99 whilst ensuring its complete stability during its trapping, the electrophilic trap reaction was conducted at 0 °C. These optimised conditions led to both the trans- and the cis-cyclopropyl sulfoxides undergoing successful sulfoxide–magnesium exchange and being trapped with a wide range of electrophiles. This formed a diverse collection of cyclopropane-containing compounds possessing a variety of functionalities and physicochemical properties. A sulfoxide–magnesium exchange, Negishi cross-coupling protocol was developed which allowed the trans- and the cis-cyclopropyl scaffolds to be directly functionalised with a variety of (hetero)aromatic rings. The sulfoxide–magnesium exchange protocols allowed a diverse range of cyclopropane-containing compounds to be divergently synthesised from the cyclopropyl sulfoxides 96 and 97. The synthesised cyclopropane-containing compounds possessed suitable physicochemical properties for use as fragments, lead-like compounds or building blocks within medicinal chemistry. The collection of synthesised cyclopropane-containing compounds possessed a diverse variety of functionalities that could be potential pharmacophores or be utilised as synthetic vectors for further derivatisation. No epimerisation was observed for any of the reactions. Additionally, no reaction was observed at the cyclopropyl ester functionality, leaving this synthetic vector intact.

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2.4. Sequential Scaffold Functionalisation using Both Synthetic Vectors A variety of methods have been developed in this work to divergently functionalise the designed bifunctional scaffolds 15 and 16 orthogonally through the ester functionality (Section 2.2) and through the sulfide functionality (Section 2.3). Having established these methods, they could then be used for the consecutive functionalisation of a single cyclopropyl scaffold to allow the generation of a huge scope of cyclopropane-containing compounds.

2.4.1. Sequential Scaffold Functionalisation: Amidation and Oxidation The first demonstration of using these methodologies for difunctionalisation of a cyclopropyl scaffold utilised a selection of the cyclopropyl amides generated in Section 2.2.2. The remaining sulfide functional handle on these cyclopropyl amides was oxidised to the corresponding sulfone, creating a small set of cyclopropyl amide sulfones 137–140 in extremely high yields (Scheme 67). For compounds 137 and 139, aqueous work-up proved problematic due to their high water solubility. This difficulty was overcome by an aqueous-free work-up. Excess mCPBA was quenched by the addition of solid Na2S2O5 to the reaction. This was followed by removal of the reaction solvent, redissolution in acetone containing 5% Et3N and filtration of the suspension. Under this procedure, after collection of the filtrate, all mCPBA derived materials had been removed, providing the sulfones in excellent purity and yield. These cyclopropane-containing compounds possessed interesting lead-like properties, with

137 and 139 having notably low lipophilicity for their MW; desirable for populating new regions of chemical space.

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R' R' R' R' mCPBA mCPBA N O N O N O (3.0 equiv) R N O (3.0 equiv) R R R CH Cl (0.02 M) CH Cl (0.02 M) 2 2 Ph 2 2 Ph Ph 25 °C, 6 h S Ph 25 °C, 6 h S S S O O O O

N N N O N O N O N O

Ph Ph Ph Ph S S S S O O O O O O O O quant. 98% quant. 86% 137 138 139 140

MW = 308 MW = 341 MW = 308 MW = 341 AlogP = 0.16 AlogP = 2.00 AlogP = 0.16 AlogP = 2.00 HBD/HBA = 0/5 HBD/HBA = 0/4 HBD/HBA = 0/5 HBD/HBA = 0/4 Fsp3 = 0.53 Fsp3 = 0.32 Fsp3 = 0.53 Fsp3 = 0.32 PSA = 57.69 Å2 PSA = 54.45 Å2 PSA = 57.69 Å2 PSA = 54.45 Å2

Scheme 67: Oxidation of amide-substituted cyclopropyl sulfides to the corresponding sulfones

2.4.2. Sequential Scaffold Functionalisation: Sulfoxide–Magnesium Exchange, Negishi Cross-Coupling and Amidation To further illustrate the synthetic potential that could be obtained by the combination of the designed bifunctional scaffolds and the orthogonal derivatisation methodologies, a second complex bifunctional cyclopropane was proposed. Synthesis was achieved by utilising the developed sulfoxide–magnesium exchange, Negishi cross-coupling, hydrolysis and amidation reactions.

Sulfoxide–magnesium exchange, Negishi cross-coupling of 96 to give pyridine-substituted cyclopropane 134 has already been demonstrated in this work, giving a 60% yield (Scheme 68). Hydrolysis of 134 to form the corresponding sodium carboxylate salt 141 in a quantitative yield followed by amidation with pyrrolidine in an 82% yield gave the desired cyclopropane product 142, functionalised with both a pyridine ring and a pyrrolidine amide (Scheme 68). This compound fits well within fragment chemical space.

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EtO O 1. NaOH(aq) (1.0 equiv) N O MW = 216 EtOH, 30 °C, 24 h AlogP = 1.35 HBD/HBA = 0/3 2. Pyrrolidine (1.2 equiv) Fsp3 = 0.54 N HATU (1.2 equiv) PSA = 33.20 Å2 DIPEA (3.0 equiv) N 134 DMF (0.2 M), 40 °C, 24 h 82% 142 Scheme 68: Hydrolysis and amidation of 134 to generate the complex bifunctional cyclopropane fragment 142 via cyclopropyl sodium carboxylate 141

2.4.3. Sequential Scaffold Functionalisation: Sulfoxide–Magnesium Exchange, Negishi Cross-Coupling and Reduction Finally, a bifunctional lead-like cyclopropane-containing compound was targeted that would possess suitable physicochemical properties for incorporation into drug discovery libraries and would also demonstrate the utility of this work. Inspiration for this was obtained from the selective serotonin reuptake inhibitor BMS-505130 (Figure 42).300 Cyclopropanes possessing similar functionality could be obtained quickly and easily through the developed sulfoxide–magnesium exchange, Negishi cross-coupling protocol and ester reduction reaction.

N HO

N S O N S O O O

BMS-505130 Target compound Bristol-Myers Squibb Selective serotonin reuptake inhibitor Figure 42: The structure of BMS-505130300 and a similar bifunctional cyclopropane

A sulfoxide–magnesium exchange, Negishi cross-coupling reaction produced the sulfonyl-protected cyclopropyl indole 143 in an excellent yield (Scheme 69). This reaction was performed on a 1.5 mmol scale and produced over 400 mg of 143, demonstrating that the sulfoxide–magnesium exchange, Negishi cross-coupling protocol could be used to generate sizeable quantities of material. Reduction of the ester on 143 produced 144 in a 94% yield.

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EtO O OH EtO O 1. i-PrMgCl (1.5 equiv) Addition time = 10 s, THF, -78 °C, 10 min LiAlH4 (2.5 equiv) Ph S 2. Pd2(dba)3 (2.5 mol%) N THF (0.3 M), 0 – 25 °C N (t-Bu) P (5.5 mol%) O 3 S S ZnCl (1.5 equiv) O Ph O Ph 97 2 THF, 0 °C, 1 h O O 75% 94% 3. Br 143 144

MW = 369 MW = 327 N AlogP = 3.43 AlogP = 2.62 O S HBD/HBA = 0/5 HBD/HBA = 1/4 3 3 O Ph Fsp = 0.25 Fsp = 0.22 2 2 (2.0 equiv) PSA = 65.37 Å PSA = 59.30 Å THF, 25 °C, 15 h Scheme 69: Sulfoxide–magnesium exchange, Negishi cross-coupling of 97 followed by ester reduction

The three examples (Schemes 68–70) demonstrate how the bifunctional scaffolds 15 and 16 can utilise the various developed methodologies to produce a wide variety of cyclopropane-containing compounds.

2.4.4. Conclusions Using methodologies developed and described in previous sections of this thesis, both synthetic handles on the designed cyclopropyl scaffolds have been utilised in orthogonal derivatisation reactions to generate a variety of cyclopropane-containing compounds. The synthesised compounds sample distinct regions of chemical space and possess a very diverse range of chemical and structural features. These compounds illustrate the enormous scope of cyclopropane-containing compounds that are possible through the orthogonal derivatisation of the bifunctional cyclopropyl scaffolds 15 and 16.

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2.5. Physicochemical Property Analysis The physicochemical properties of a compound have a dramatic effect on the way that that compound behaves in the body and as such, compound physicochemical properties are carefully analysed within medicinal chemistry (Sections 1.2–1.5). Two of the most important physicochemical properties for medicinal chemistry are lipophilicity and MW. These parameters are often plotted against each other on a graph as a useful way to analyse these important molecular properties for both individual compounds and entire libraries.

It has been found that compound libraries within medicinal chemistry contain an over-representation of linear and flat compounds.302 The 3-dimensionality of a compound can be represented with a Principal Moments of Inertia (PMI) plot.303 A recent analysis by Morley and co-workers analysed a library of around 1000 fragments that were reportedly representative of commercial fragment space and found that the majority occupied the region of chemical space close to the rod-like–disk-like axis (Figure 43).302

Figure 43: A PMI plot of approximately 1000 fragments representative of commercial chemical space by Morley and co-workers302

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As such, a variety of physicochemical properties as well as 3D shape features for the synthesised cyclopropane-containing compounds were calculated to ensure that they were desirable for use within medicinal chemistry.

2.5.1. Synthesised Cyclopropane-Containing Compounds The physicochemical properties for the synthesised cyclopropane-containing compounds are shown in Figure 44.291 The properties were calculated using the Lead Likeness and Molecular Analysis (LLAMA) computational tool, developed by Nelson, Marsden and co-workers.291 The LLAMA tool estimates lipophilicity using AlogP calculations instead of the more commonly-used term of clogP. This is due to LLAMA calculating the atomic logP (addition of individual atomic logP contributions)291 opposed to the compound logP (calculated using experimental values for smaller compounds and modelling using regression techniques).

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O O O O HO O HO O

S S S S 15 16 79 80

MW = 222 MW = 222 MW = 194 MW = 194 AlogP = 3.21 AlogP = 3.21 AlogP = 2.44 AlogP = 2.44 HBD/HBA = 0/2 HBD/HBA = 0/2 HBD/HBA = 1/2 HBD/HBA = 1/2 Fsp3 = 0.416 Fsp3 = 0.416 Fsp3 = 0.300 Fsp3 = 0.300 PSA = 26.30 Å2 PSA = 26.30 Å2 PSA = 37.30 Å2 PSA = 37.30 Å2

O N H N O N O N O N O

S S S S 84 85 86 87

MW = 283 MW = 263 MW = 276 MW = 309 AlogP = 3.51 AlogP = 1.98 AlogP = 1.75 AlogP = 4.08 HBD/HBA = 1/2 HBD/HBA = 0/3 HBD/HBA = 0/3 HBD/HBA = 0/2 Fsp3 = 0.235 Fsp3 = 0.50 Fsp3 = 0.53 Fsp3 = 0.32 PSA = 29.10 Å2 PSA = 29.54 Å2 PSA = 23.55 Å2 PSA = 20.31 Å2

O N H N O N O N O N O

S S S S 83 88 89 90

HO HO O O O O

S S S S O O O O 91 92 94 95

MW = 180 MW = 180 MW = 254 MW = 254 AlogP = 2.74 AlogP = 2.74 AlogP = 1.24 AlogP = 1.24 HBD/HBA = 1/1 HBD/HBA = 1/1 HBD/HBA = 0/4 HBD/HBA = 0/4 Fsp3 = 0.400 Fsp3 = 0.400 Fsp3 = 0.417 Fsp3 = 0.417 PSA = 20.23 Å2 PSA = 20.23 Å2 PSA = 60.44 Å2 PSA = 60.44 Å2

O O O O O O O O

S S O O OH OH 96 97 108 109

MW = 238 MW = 238 MW = 212 MW = 220 AlogP = 0.82 AlogP = 0.82 AlogP = 1.91 AlogP = 2.09 HBD/HBA = 0/3 HBD/HBA = 0/3 HBD/HBA = 1/3 HBD/HBA = 1/3 Fsp3 = 0.42 Fsp3 = 0.42 Fsp3 = 0.92 Fsp3 = 0.46 PSA = 43.37 Å2 PSA = 43.37 Å2 PSA = 46.53 Å2 PSA = 46.53 Å2

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O O O O O O O O

N OH OH OH

OH Cl N O N

Cl 110 111 112 113

MW = 221 MW = 186 MW = 365 MW = 298 AlogP = 1.08 AlogP = −0.16 AlogP = 5.05 AlogP = 1.98 HBD/HBA = 1/4 HBD/HBA = 1/4 HBD/HBA = 1/3 HBD/HBA = 1/5 Fsp3 = 0.50 Fsp3 = 0.89 Fsp3 = 0.32 Fsp3 = 0.35 PSA = 59.42 Å2 PSA = 55.76 Å2 PSA = 46.53 Å2 PSA = 72.31 Å2

O O O O O O O O O O S O HN

114 115 116 120

MW = 218 MW = 233 MW = 252 MW = 166 AlogP = 2.19 AlogP = 1.81 AlogP = 3.53 AlogP = 2.04 HBD/HBA = 0/3 HBD/HBA = 1/4 HBD/HBA = 0/3 HBD/HBA = 0/2 Fsp3 = 0.38 Fsp3 = 0.38 Fsp3 = 0.46 Fsp3 = 0.90 PSA = 43.37 Å2 PSA = 55.40 Å2 PSA = 35.53 Å2 PSA = 26.30 Å2

O O O O O O O O N OH

OH Cl

121 122 123 Cl 124

MW = 174 MW = 221 MW = 154 MW = 365 AlogP = 1.90 AlogP = 1.08 AlogP = 2.25 AlogP = 5.05 HBD/HBA = 0/2 HBD/HBA = 1/4 HBD/HBA = 0/2 HBD/HBA = 1/3 Fsp3 = 0.36 Fsp3 = 0.50 Fsp3 = 0.89 Fsp3 = 0.32 PSA = 26.30 Å2 PSA = 59.42 Å2 PSA = 26.30 Å2 PSA = 46.53 Å2

O O O O O O O O OH N N N O N

125 126 127 129

MW = 298 MW = 252 MW = 218 MW = 190 AlogP = 1.98 AlogP =2.13 AlogP = 2.19 AlogP = 2.95 HBD/HBA = 1/5 HBD/HBA = 0/4 HBD/HBA = 0/3 HBD/HBA = 0/2 Fsp3 = 0.35 Fsp3 = 0.27 Fsp3 = 0.38 Fsp3 = 0.42 PSA = 72.31 Å2 PSA = 52.08 Å2 PSA = 43.37 Å2 PSA = 26.30 Å2

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O O O O O O O O

Cl O 130 131 132 133

MW = 190 MW = 225 MW = 220 MW = 216 AlogP = 2.95 AlogP = 3.45 AlogP = 3.20 AlogP = 3.81 HBD/HBA = 0/2 HBD/HBA = 0/2 HBD/HBA = 0/3 HBD/HBA = 0/2 Fsp3 = 0.42 Fsp3 = 0.42 Fsp3 = 0.46 Fsp3 = 0.36 PSA = 26.30 Å2 PSA = 26.30 Å2 PSA = 35.53 Å2 PSA = 26.30 Å2

N O O O O O O N O

N S N N N O O O O

134 135 136 137

MW = 191 MW = 192 MW = 329 MW = 308 AlogP = 1.31 AlogP = 0.56 AlogP = 4.39 AlogP = 0.16 HBD/HBA = 0/3 HBD/HBA = 0/4 HBD/HBA = 0/5 HBD/HBA = 0/5 Fsp3 = 0.46 Fsp3 = 0.5 Fsp3 = 0.47 Fsp3 = 0.53 PSA = 39.19 Å2 PSA = 52.08 Å2 PSA = 57.53 Å2 PSA = 57.69 Å2

N N O N O N O N O

S S S O O O O O O N

138 139 140 142

MW = 341 MW = 308 MW = 341 MW = 216 AlogP = 2.00 AlogP = 0.16 AlogP = 2.00 AlogP = 1.35 HBD/HBA = 0/4 HBD/HBA = 0/5 HBD/HBA = 0/4 HBD/HBA = 0/3 Fsp3 = 0.32 Fsp3 = 0.53 Fsp3 = 0.32 Fsp3 = 0.54 PSA = 54.45 Å2 PSA = 57.69 Å2 PSA = 54.45 Å2 PSA = 33.20 Å2

O O OH

N N O S O S O O

143 144

MW = 369 MW = 327 AlogP = 3.43 AlogP = 2.62 HBD/HBA = 0/5 HBD/HBA = 1/4 Fsp3 = 0.25 Fsp3 = 0.22 PSA = 65.37 Å2 PSA = 59.30 Å2 Figure 44: Physicochemical properties of the synthesised compounds calculated by the LLAMA software291

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The physicochemical properties for compounds 106, 107, 117, 118, 119 and 128 were not included due to their possession of functionality that would be undesirable for compound screening. The small library of compounds produced by the divergent functionalisation of cyclopropyl scaffold 15 and 16 possess varied physicochemical properties and fit within either fragment or lead-like chemical space (Figure 44).

To analyse the MW and AlogP diversity of the library, the AlogP value for each compound was plotted against its MW (Graph 3). The plot showed that the small library of compounds sampled a large range of lipophilicities and MW’s, with a weak positive correlation between the two parameters. The weak positive correlation between the

AlogP and the MW in the library produced by this methodology showed that regions of chemical space that are typically difficult to sample, e.g. high MW compounds with a polar nature, could be readily accessed through this approach.

AlogP 2

0 100 150 200 250 300 350 400 !1 Mw0(Da)

Graph 3: AlogP vs. MW plot for the synthesised cyclopropane-containing compounds

Using the LLAMA software, a PMI plot for these compounds was generated (Figure 45). The small library of synthesised cyclopropane-containing compounds sampled a large range of chemical space, with the compounds being located away from the frequently-overpopulated rod-like–disk-like axis. This confirmed that the synthesised cyclopropanes possessed significant 3-dimensionality.

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HO O HO O

SPh SPh 80 79

Sphere-like Rod-like

O O

N O OH

N N SPh 87 113

O O

N O OH

N N SPh 90 Disk-like 125

Figure 45: A plot produced from the LLAMA-generated PMI data for the synthesised cyclopropane-containing compounds

Three pairs of diastereoisomers have been illustrated in Figure 45, showing both the trans- and cis-diastereoisomers, highlighting the difference that the cyclopropane configuration can make on the 3-dimensional structure of the compound.

2.5.2. Virtual Cyclopropane-Containing Compounds A feature of the LLAMA software was that it allowed the virtual derivatisation of molecular scaffolds using a limited set of common transformations and a library of reactants.291 This feature was utilised in the virtual derivatisation of the cyclopropane-containing compounds synthesised in this work, this time including the cyclopropyl building blocks 106, 107, 117, 118, 119 and 128. The cyclopropane-containing compounds were virtually functionalised using the default LLAMA set of reactants (Figure 46).

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O Cl O O O O O O O O C F S O S S S Cl N Cl Cl S O Cl F N N F O N

O OH N OH F O N N C HN B NH O B F O HN 2 N F OH N OH

NH2 N OH N N HN N B N Br Br H HN NH2 N OH N N H N O O O OH O HO F C OH O N N O N O

N F O HO N O OH O O Br Br O OH Br O O OH N S NH2 F O Cl N B Br N O C OH N N O O O O OH C OH O NH N O N N N H

Br O

HO O N Figure 46: The default LLAMA reactant set

The default set of transformations that could be used by the software did not include an ester hydrolysis reaction, which meant that the ester functionality on the bifunctional cyclopropanes could not undergo theoretical functionalisation. Therefore, the hydrolysis of an ester to form the corresponding carboxylic acid was enabled by adding a piece of SMARTS code (Figure 47) via ‘Advanced settings > Add a new reaction to the library’.

[*;$([CX3](=O)):1][OX2H0][#6]>>[*:1][OX2H1]

Figure 47: SMARTS code to enable the ester hydrolysis reaction to produce the corresponding carboxylic acid

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This meant that the set of reactions that could be employed by the software consisted of BOC deprotection, reductive amination, Suzuki-Miyaura cross-coupling, Buchwald-Hartwig amination, sulfonamide formation, urea formation, alcohol alkylation, carbamate formation, secondary amide alkylation, secondary amide arylation, amide formation, alcohol arylation, urea alkylation, urea arylation, esterification and ester hydrolysis.

Submitting the 56 synthesised cyclopropane-containing compounds for virtual functionalisation with the set of 44 default reactants and allowing a maximum of two functionalisations from the enabled reaction set generated 1187 compounds (Figure 48).

Up to 2 reactions using: 500 Da < MW BOC deprotection 153 Compounds Reductive amination Suzuki-Miyaura cross-coupling Buchwald-Hartwig amination Drug-Like Compounds Sulfonamide formation 400 Da < M < 500 Da Urea formation W 56 44 275 Compounds Alcohol alkylation Cyclopropane LLAMA 1187 Containing Default Compounds Carbamate formation Compounds Reactants MW Secondary amide alkylation Lead-Like Compounds Secondary amide arylation 300 Da < MW < 400 Da Amide formation 366 Compounds Urea alkylation Urea arylation Esterification Fragments Ester hydrolysis 300 Da < MW 393 Compounds Figure 48: Theoretical derivatisation of the synthesised bifunctional cyclopropanes

The number and variety of synthetic vectors on the synthesised cyclopropane-containing compounds allowed a substantial virtual library of cyclopropane-containing compounds to be generated. An AlogP vs. MW plot was constructed for these virtually generated compounds which showed that the compound library sampled fragment, lead-like and drug-like chemical space to a sizeable degree (Graph 4).

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8 7 6 5 4 3 AlogP 2 1 0 0 100 200 300 400 500 600 700 !1 !2 Mw2(Da)

Graph 4: AlogP vs. MW plot for the theoretically-functionalised cyclopropanes

Constructing a PMI plot with the data for the 1187 compounds demonstrated that these derivatised cyclopropane-containing compounds sampled a huge amount of chemical space, possessing varied 3-dimensional structures (Figure 49). The compounds occupied regions of chemical space that were distant from the rod-like–disk-like axis, with many compounds possessing PMI data points around the centre of the plot.

Rod-like Sphere-like

Disk-like

Figure 49: PMI plot for the 1187 theoretically-functionalised cyclopropane-containing compounds

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Through the use of AlogP vs. MW (Graph 4) and PMI (Figure 49) plots it was clear that the library of virtually functionalised cyclopropane-containing compounds both contained compounds that possessed appropriate physicochemical properties for use within drug discovery and contained a vast amount of shape diversity that explored less-populated regions of chemical space.

2.5.3. Conclusions The physicochemical properties of the individual synthesised cyclopropane-containing compounds have been calculated and the compound collection has been analysed with MW vs. AlogP and PMI plots. The compounds fit well within fragment or lead-like chemical space, and would be useful when incorporated into an existing drug discovery compound library. The collection of cyclopropane-containing compounds samples a large amount of chemical space, with a considerable variety of 3-dimensional structures present. The PMI data points for the synthesised compounds were located significantly away from the frequently-overpopulated rod-like–disk-like axis, in a region of chemical space that is of substantial interest within medicinal chemistry. The synthesised cyclopropane-containing compounds were virtually derivatised with the LLAMA software.291 This virtual derivatisation of 56 synthesised cyclopropanes with the default LLAMA library of 44 reactants, in ≤ 2 reactions using common medicinal chemistry transformations generated 1187 cyclopropane-containing products. These theoretical compounds occupied fragment, lead-like and drug-like chemical space, and possessed an enormous amount of shape diversity.

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3. Conclusions and Future Work 3.1. Conclusions A CoII-catalysed cyclopropanation of PVS with EDA has been developed for the synthesis of the desired trans- and cis-bifunctional cyclopropyl scaffolds (Scheme 70). Notable characteristics of the developed cyclopropanation include that it is scalable, being capable of generating multi-gram quantities of the products from a single reaction. In addition, the CoII(salen)-type catalyst is air and moisture stable, meaning a glovebox is not required for its storage and handling. Furthermore, the CoII catalyst does not cause dimerisation of the diazo reagent, meaning that a slow addition protocol using a syringe pump is not required and that the diazo reagent can be used as the limiting reagent, reducing the quantity used in the reaction and hence increasing the safety of the method. These factors make the cyclopropanation extremely practical.

•No glovebox required •No syringe pump required •Commercially available catalyst

N N Co t-Bu O O t-Bu

t-Bu t-Bu 28 O EtO O EtO O (5 mol%) S EtO Ph H2O, 40 ºC, 24 h Ph Ph N2 S S (1.5 equiv) 15 16

•Commercially available reagents •Green reaction solvent304 •Excellent yields •Scalable (up to 40 mmol demonstrated) Scheme 70: Overview of the developed CoII-catalysed cyclopropanation of PVS with EDA.304

The asymmetric cyclopropanation of PVS with EDA was examined with a variety of CuI(BOX), CuI(PyBOX) and CoII(salen)-type complexes. The investigation led to two sets of prominent conditions being developed for enantiopure CoII(salen)-type complex 28*, inducing enantioenrichments of 56% (trans) and 77% (cis) (Scheme 71).

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N N Co t-Bu O O t-Bu

t-Bu t-Bu 28* O EtO O EtO O S (5.0 mol%) EtO solvent, temperature, 24 h N2 S S (1.5 equiv) 15* 16*

Conditions: Cyclohexane, 25 °C trans ee = 56% cis ee = 74%

Conditions: H2O, 20 °C trans ee = 52% cis ee = 77% Scheme 71: Optimised enantioselective CoII-catalysed cyclopropanation of PVS with EDA

Using chiral supercritical fluid chromatography, enantiopure samples of 15 and 16 were obtained. X-ray crystallography of the corresponding sulfones allowed the absolute configurations of each isomer, and hence the absolute configuration of the precursor sulfides, to be determined.

Having developed practical access to the trans- and cis-bifunctional cyclopropyl scaffolds 15 and 16, the ethyl ester functionality was divergently derivatised through hydrolysis, amidation, reduction and esterification reactions (Scheme 72).

Oxidation of the sulfide on scaffolds 15 and 16 was achieved, enabling the corresponding sulfoxides or sulfones to be obtained selectively and in excellent yields. Conditions for sulfoxide–magnesium exchange have been developed for cyclopropyl sulfoxides 96 and 97, with the stability of the trans-cyclopropyl Grignard 96 being investigated. These stability investigations showed that the Grignard intermediate was stable for multiple hours up to 0 °C, but became unstable at 25 °C. This allowed the reactivity of the cyclopropyl Grignard to be maximised whilst retaining its stability under the reaction conditions. This resulted in a wide variety of electrophiles being successfully utilised in the electrophilic trapping of the cyclopropyl Grignard intermediates derived from 96 and 97 and in doing so, generated a variety of cyclopropane-containing compounds (Scheme 72). The cyclopropyl Grignard

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intermediates were also utilised in Negishi cross-coupling reactions, allowing the intact cyclopropane ring to be directly functionalised with a range of aromatic and heteroaromatic rings (Scheme 72).

R2 Stereochemistry retained N O for all transformations R1

Ph HO O S

NaO O RO O Ph S Ph Ph S S EtO O HO EtO O E Ph S EtO O Ph S Ph S O

EtO O EtO O

Ph S O O (Het)Ar

Scheme 72: Divergent derivatisation of the bifunctional cyclopropyl scaffolds 15 and 16

The physicochemical properties of the synthesised cyclopropane-containing compounds were calculated and plotted in AlogP vs. MW and PMI plots to illustrate the chemical space that the compound collection sampled. The compounds were found to sample a large amount of chemical space and possessed a wide range of 3-dimensional structures that were located significantly away from the rod-like–disk-like axis. The synthesised fragments, lead-like compounds and building blocks were submitted to virtual derivatisation with the LLAMA computational tool. This generated a collection of 1187 cyclopropane-containing compounds which also displayed a broad distribution of medicinally-relevant physicochemical properties and 3-dimensional structures.

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In summary, a fast and efficient route has been developed to generate trans- and cis-bifunctional cyclopropyl scaffolds, which can be orthogonally derivatised through a variety of reactions in a divergent manner to synthesise medicinally-relevant compounds.

Future project-oriented work should be directed towards a variety of targets, each extending on from the methodology that has already been developed.

3.2. Future Work: Biological Screening The cyclopropane-containing fragments and lead-like compounds that have been synthesised in this work should be submitted for biological screening against a variety of biological targets.

3.3. Future Work: Asymmetric Cyclopropanation Another area of future work is to improve on the asymmetric induction achieved already through the design and synthesis of suitable enantiopure CoII-catalysts. Towards this aim, complexes were designed that possessed the advantages of two related commonly used ligand structures; salen-type and porphyrin. Enantioenriched salen-type complexes generally require fewer synthetic steps to synthesise than enantioenriched porphyrin complexes. Additionally, the chirality of a salen-type complex is located closer to the reactive metal centre than for a porphyrin complex, suggesting higher transfer of chiral information may be possible. However, salen-type complexes are known to twist conformation depending on a variety of factors including the transition metal used and the presence of any external ligands.305 This makes predicting or explaining the stereochemical induction of a salen-type complex less than trivial. In contrast, porphyrin complexes retain their rigidity and are therefore much less conformationally varied.306 Consequently, the resulting complex designs should benefit from the increased synthetic ease and closer chirality location associated with a salen-type complex and the rigidity associated with a porphyrin complex. Additional benefits that were desired were stability of the complex towards silica chromatography to allow facile separation and reuse, and a relatively inexpensive source of chirality.

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Towards this aim, two salenophen-related ligands have been designed. The first proposed catalyst design, complex 145, makes use of the salen-type scaffold architecture, possessing chirality attached to the imine functionality as opposed to a conventional chiral diamine backbone used in typical salen-type complexes (Figure 50). In 2001, Katsuki proposed that during transition metal(salen)-type complex-catalysed cyclopropanation the alkene approached by crossing the imine functionality (illustrated previously in Scheme 36).199 Having the chirality located at this mechanistically-important region of the complex may allow better chiral induction between the complex and the cyclopropanation transition state. Additionally, adding substitution to the imine would make it less electrophilic and therefore more resistant to decomposition, potentially allowing its isolation and reuse through silica chromatography of the cyclopropanation reaction mixture.

Me F F Ph Me Ph N N Co O O

145 II Figure 50: Structure of designed C2-symmetric Co -complex 145

In addition to the bond linking it to the imine carbon, the chiral carbon would possess three groups of distinctly different sizes, allowing steric differentiation. This steric II differentiation of the groups would generate a C2-symmetric Co -complex. The first step in the synthesis of 145 would be the fluorination of 2-phenylpropionic acid 146 or 2-phenylpropionyl chloride 148 to generate 149 (Scheme 73). Fluorine would be required as a replacement for a proton due to the acidity of the position a to the carbonyl. Not substituting this proton would leave the enantioenriched ligand vulnerable to base-mediated epimerisation. The incorporation of fluorine should still allow steric differentiation between itself, a methyl and a phenyl group. The transformation could be achieved through a racemic fluorination as demonstrated by Zhang and co-workers to give 147,307 followed by a chiral resolution with (S)-(–)a-methyl benzylamine as demonstrated by Hamman (Scheme 73, route a),308 or an asymmetric fluorination of acyl chloride 148 utilising an Evans chiral auxiliary

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(Scheme 73, route b).309 The reaction with 2,4-di-tert-butylphenol to generate 150 could be carried out using a protocol by Nicolaou and co-workers,310 which would be followed by diamine formation to give Schiff base 151 and cobalt complexation to yield II the desired C2-symmetric Co -complex 145.

Route a Me H TBSCl Me F (S)-(–)-∝-Methyl OH LiHMDS OH benzylamine

O Select-Fluor O 146 147

Route b 1a. BuLi 1b. Me H t-Bu OH Me F O 148 O Me F t-Bu O HN O Cl O 3. BuLi, SelectFluor BF3·Et2O t-Bu OH HO 4. LiOH, H2O2 120 °C, 2 h 149 150 t-Bu

H2N NH2 (0.5 equiv) EtOH, reflux

Me F F Me F F Me Me Co(OAc)2 N N N N Co EtOH, reflux t-Bu O O t-Bu t-Bu OH HO t-Bu

t-Bu t-Bu t-Bu t-Bu 145 151

Scheme 73: Proposed synthetic routes to CoII-complex 145

An alternative asymmetric ligand, 152, and the corresponding CoII-complex, 153, were also designed as part of this work but have not yet been synthesised (Figure 51A). This design would possess similar benefits to those outlined for complex 145, however in addition, it was anticipated that the chiral arms of the C2-symmetric ligand (highlighted in blue, Scheme 51B) would also interact with the carbonyl of the cobalt carbene intermediate (red, Figure 51B) via a hydrogen bond. This interaction would generate a strong conformational preference for the carbene during the cyclopropanation reaction. Such hydrogen bonding interactions have been used to great effect by Zhang and co-workers in enantioselective CoII(porphyrin)-catalysed

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cyclopropanations.130 As discussed in Section 2.1.4.2, successful asymmetric induction in a cyclopropanation reaction proceeding via carbene insertion relies on three requirements being fulfilled; control over the carbene orientation, control over the alkene approach trajectory and control over the alkene orientation. The hydrogen bonding interaction is expected to fulfil the first of these requirements. The chiral arm is anticipated to act as an effective obstruction towards reaction from one side of the complex, fulfilling the second requirement. Finally, the alkene approach trajectory would result in the incoming alkene passing within close proximity to one of the fluoro-substituted aromatic rings on complex 153 (pink, Figure 51B). This would be expected to generate alkene facial selectivity, favouring the alkene orientation that minimises steric repulsion between its substituents and the fluoro-substituted ring. This interaction could fulfil the third requirement for successful asymmetric induction; control of the alkene orientation. If successful, these factors would result in the CoII complex generating highly enantioenriched cyclopropanes, with the potential for the ligand to be used in other asymmetric transition metal-catalysed reactions.

A) B)

R' O OH H R' O H O O N N F F O Co R' = OH Co N F F F O S O N F R' R'

153

Figure 51: A) Designed structure for complex 153. B) Potential asymmetric induction mechanism for the 153-catalysed cyclopropanation of EDA with PVS

The proposed synthesis of CoII complex 153 begins with a formylation of 154 to give 155, followed by a one-pot borylation, Suzuki-Miyaura cross-coupling sequence to generate 157 (Scheme 74). Such one-pot cross-coupling reactions have been reported, with a notable example being produced by Molander, Trice and Kennedy.311 The presence of two fluoro substituents on aryl bromide 156 in the Suzuki-Miyaura cross-coupling reaction allow regiocontrol in the upcoming I2-promoted ring closure

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step and result in slightly greater conformational rigidity to the chiral side-arms. A Heck reaction would install a substantial portion of the chiral side-arm which would be followed by the I2-promoted ring closure reaction at the only available position to give aldehyde 160.

Borylation, Suzuki-Miyaura cross-coupling

Formylation 1) XPhos-Pd-G2 (1 mol%) XPhos (2 mol%) (CH2O)n, Et3N O B2(OH)4, KOAc OH MgCl2, MeCN EtOH (0.1 M), 80 ºC OH Br Br 2) Br Br Br OH O 154 155 F F F F 156 157

R' = OH R = Cl Heck Cl reaction OH Borylation, Suzuki-Miyaura cross-coupling 158 1) XPhos-Pd-G2 (1 mol%) XPhos (2 mol%) Cl H B2(OH)4, KOAc R' EtOH (0.1 M), 80 ºC R I2, UV H R' R 2) Br OH OH O OH O OH O F F F F F F 162 160 159 OH 161

Separation of enantiomers

R' R' R' R' H N NH 2 2 OH N O N R' 164 F F Co(OAc)2 F F Co R' F F F F OH N EtOH O N reflux OH O F F R' R' 163 R' R'

152 153

Scheme 74: Designed structures and proposed synthesis of ligand 152 and CoII-complex 153. References for 312,313 311 314,315 conditions: Formylation. Borylation, Suzuki-Miyaura cross-coupling. I2-mediated cyclisation. Potential conditions for di-imine formation and CoII complexation can be found in the experimental section of this thesis.

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Borylation and Suzuki-Miyaura cross-coupling of 160 with 3,5-dihydroxybromobenzene 161 would generate the racemic salicylaldehyde-related component of the ligand, 162. Chiral separation of the two enantiomers would produce the enantiomerically pure 163, along with its enantiomer. Condensation of 163 with 1,2-diaminobenzene 164 would produce the desired enantiopure ligand 152. Cobalt II insertion with a Co salt such as Co(OAc)2 would result in the designed CoII(salen)-type complex 153.

3.4. Recovery of CoII Catalyst Future work could also focus on developing a method for the regeneration of the CoII catalyst after oxygenation with air. One approach towards this may be through the use of hydroquinone as a reducing agent which has been shown to facilitate the removal 316 of bound O2 from transition metal complexes.

3.5. Expansion of the Cyclopropyl Scaffold Derivatisation Methodology Future work should be conducted on developing more reactions that can be performed on the bifunctional cyclopropane scaffolds to further increase the number and variety of cyclopropane-containing compounds that can be created from them.

One such reaction that should be investigated is the decarbonylative organoboron cross-coupling of the cyclopropyl ester functionality. Muto and co-corkers have described a nickel-catalysed cross-coupling of aryl esters with boronic acids.317 An aryl ester was required for the reaction to proceed and ethyl esters were found to be virtually unreactive under the otherwise identical conditions, however it has been demonstrated in this thesis that a phenyl ester-substituted cyclopropane can be synthesised in an excellent yield (Section 2.2.4). This reaction is proposed to proceed via a transmetalation–decarbonylation pathway, which offers the possibility of retention of stereochemical information adjacent to the ester carbonyl.317 The reaction was largely demonstrated on aromatic esters, however there were limited examples using benzylic esters, giving moderate yields.317 If successful, this methodology would allow the installation of (hetero)aromatics onto the intact cyclopropane ring, utilising

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the ester functionality. This would be complementary to the sulfoxide–magnesium exchange, Negishi cross-coupling protocol utilised on scaffolds 15 and 16 in this work.

Another alternative method of functionalisation that should be investigated is the transformation of the cyclopropyl ethyl ester of scaffolds 15 and 16 into an amine. Amine-substituted and more generally nitrogen-substituted cyclopropanes are widely found within pharmaceutical drugs and are a very important motif within medicinal chemistry (Figure 52).

S O OH O I NH3Cl N N N

N NH N N N O HO H H N N F OH F O N O

F (±)-Tranylcypromine⋅HCl Ticagrelor Trametinib (Mekinist) Monoamine oxidase inhibitor AstraZeneca GlaxoSmithKline Depression Platelet aggregation inhibitor MEK inhibitor MAO A (Ki = 19 µM) Anti-cancer activity MAO B (Ki = 16 µM) P-MEK (Ki = 12 nM) Figure 52: Examples of pharmaceutically-relevant nitrogen-substituted cyclopropanes. References: (±)Tranylcypromine×HCl.318 Ticagrelor.298 Trametinib.319

Routes to form an amine-substituted cyclopropane from an ethyl ester-substituted cyclopropane exist (Scheme 75),320 and the transformation should be tested on cyclopropyl scaffolds 15 and 16 to demonstrate that the scaffolds are compatible with the reaction conditions, allowing access to the cyclopropyl amine motif.

1) 1 M NaOH, EtOH O O NH 2) (i) DPPA, Et3N, t-BuOH 2 (ii) Boc2O OMe OMe 3) (i) TFA, CH2Cl2 (ii) 1 M HCl, Et2O 49%

Scheme 75: A route to form an amine-substituted cyclopropane from an ester-substituted cyclopropane by Hyland and co-workers320

In addition, methodology could be explored for the formation of a cyclopropyl amine through the developed sulfoxide–magnesium exchange followed by trapping with an

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electrophilic nitrogen source, such as that developed by Narasaka and co-workers using 4,4,5,5-tetramethyl-1,3-dioxolan-2-one O-sulfonyloxime (Scheme 76).321

CO Et 2 1) i-PrMgCl (1.5 equiv) CO2Et THF, −78 °C, 10 min Ph S 2) OSO Ph O N 2 NH3Cl

O O (2.0 equiv)

THF, 0 °C 3) Acidic work-up Scheme 76: Proposed route to amine-substituted cyclopropanes via a sulfoxide–magnesium exchange protocol

Another synthetic transformation that could be explored using the methodology that has been developed for cyclopropyl scaffolds 15 and 16 is the trapping of the cyclopropyl Grignard intermediate with an electrophilic fluorinating agent, generating the corresponding fluorine-substituted species. Fluorine-substituted cyclopropanes are medicinally-relevant motifs and it would be highly desirable to be able to synthesise such a motif (Figure 53).

Cl CN

O N NH N N NH F HN NH N

HN O N F

HN F Tyrosine protein kinase inhibitor p21-Activated kinase inhibitor Ki (TYK2) = 1.6 nM Ki (PAK1) = 11 nM Figure 53: Examples of medicinally-relevant compounds possessing the cyclopropyl fluoride motif. References: TYK2 inhibitor.322 PAK1 inhibitor.323

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4. Experimental 4.1. General Experimental Considerations All non-aqueous reactions were run under an inert atmosphere (argon) with flame-dried glassware using standard techniques. Anhydrous solvents were obtained by filtration through drying columns (THF, CH2Cl2, toluene, DMF). Where applicable, rt denotes a room temperature of approximately 22 °C, and a specifically noted temperature e.g. “stirred at 25 °C” indicates the stated temperature was accurately maintained.

Flash column chromatography was performed using 230–400 mesh silica with the indicated solvent system according to standard techniques. Analytical thin-layer chromatography (TLC) was performed on precoated, glass-backed silica gel plates. Visualisation of the developed chromatogram was performed by UV absorbance (254 nm), aqueous potassium permanganate, vanillin, ninhydrin or p-anisaldehyde stains as appropriate.

-1 Infrared spectra (nmax, FTIR ATR) were recorded in reciprocal centimetres (cm ).

Nuclear magnetic resonance spectra were recorded on 400 or 500 MHz spectrometers. Chemical shifts for 1H NMR spectra are recorded in parts per million from tetramethylsilane with the solvent resonance as the internal standard (chloroform: d = 7.27 ppm, DMSO: d = 2.50 ppm). Data is reported as follows: chemical shift [multiplicity (s = singlet, d = doublet, t = triplet, m = multiplet and br = broad), coupling constant in Hz, integration, assignment]. 13C NMR spectra were recorded with complete proton decoupling. Chemical shifts are reported in parts per million from 13 tetramethylsilane with the solvent resonance as the internal standard ( CDCl3: d = 13 1 77.0 ppm, ( CD3)2SO: d = 39.5 ppm). J values are reported in Hz. Assignments of H and 13C spectra were based upon the analysis of d and J values, as well as COSY, HSQC, HMBC and NOESY experiments where appropriate.

Melting points are uncorrected.

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Optical rotations (a’) were recorded in CHCl3 at the indicated temperature (T °C) and were converted to the corresponding specific rotations [�].

Commercial reagents were used as supplied or purified by standard techniques where necessary.

Use of diazo compounds: Although we have not experienced any problems in the handling or reaction of diazo reagents, extreme care should be taken when manipulating them due to their potentially explosive nature.

CuI-catalysed cyclopropanation: For the CuI-catalysed procedure, all catalysts were stored in a desiccator, except for CuIOTf which was stored and handled in a glovebox. Reactions were conducted in a sealed microwave vial. Slow addition of the diazo compound solution was achieved with a syringe pump.

CoII-catalysed cyclopropanation: For the CoII-catalysed procedure, no special precautions were taken to exclude air or moisture from the catalyst during storage or handling. After all reagents were added, the reaction vessel was sealed with either a crimp seal microwave vial lid with a septum, or a suba seal and the reaction vessel flushed with Ar(g). Ar(g) flushed, deflated balloons were attached to the flask, so that the total potential volume of the balloons when inflated was greater than the volume of N2(g) evolved from the reaction. On scales where ≥ 10 mmol of diazo compound were used, a precautionary blast shield was placed between the reaction flask and the fume hood sash.

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4.2. Experimental Details and Characterisation Data

Synthesis of 15 and 16 by CoII-catalysed cyclopropanation

(trans)-Ethyl 2-(phenylsulfanyl)cyclopropane-1-carboxylate (15) and (cis)-Ethyl 2-(phenylsulfanyl)cyclopropane-1-carboxylate (16)

O O O Hc Hc O H Hd a H Ha d Hb S Hb S 15 16

A flask containing (±)N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino cobalt(II) (28) (1.21 g, 2.0 mmol, 5 mol%) was flushed with Ar(g) for 15 min. Water

(80 mL, degassed with Ar(g)), phenyl vinyl sulfide (7.84 mL, 60 mmol, 1.5 equiv) and ethyl diazoacetate (4.84 mL, containing 13 wt% CH2Cl2, 40 mmol, 1.0 equiv) were added and the mixture was warmed to 40 °C. After stirring at 40 °C for 24 h, the mixture was cooled to rt. i-Hexane (20 mL) was added and air bubbled through the stirring mixture for 15 min. Filtration of the mixture through a pad of silica, washing with

CH2Cl2, followed by purification by flash column chromatography (15:1 pentane:Et2O) gave (trans)-ethyl 2-thiophenylcyclopropane carboxylate 15 (3.66 g, 41%) as a yellow oil followed by (cis)-ethyl 2-thiophenylcyclopropane carboxylate 16 (4.25 g, 48%) as a yellow oil.

(trans)-Ethyl 2-(phenylsulfanyl)cyclopropane-1-carboxylate (15) -1 Rf = 0.54 (4:1 n-hexane:Et2O). IR (film)/cm 3078 (CH), 3059 (CH), 2981 (CH), 2941 1 (CH), 2906 (CH), 1725 (C=O), 1584, 1480, 1380. H NMR (400 MHz, CDCl3) d

7.35–7.28 (m, 4 H, 4 × Ph-H), 7.21-7.17 (m, 1 H, Ph-H), 4.25–4.13 (m, 2 H, CH2CH3),

2.77 (ddd, J = 8.5, 5.6, 3.6 Hz, 1 H, Hc), 1.92 (ddd, J = 8.5, 5.4, 3.6 Hz, 1 H, Hd), 1.67

(ddd, J = 8.5, 5.4, 4.9 Hz, 1 H, Hb), 1.29 (t, J = 7.1 Hz, 3 H, CH3), 1.25 (ddd, J = 8.5, 13 5.6, 4.9 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 172.3 (C=O), 136.8 (Ph-C quat),

128.9 (2 × Ph-C), 127.2 (2 × Ph-C), 125.7 (Ph-C), 61.0 (CH2CH3), 24.2 (C(Hd)), 22.3 + + (C(Hc)), 17.2 (C(Ha)(Hb)), 14.2 (CH3). HRMS (ES) m/z Calcd for C12H15O2S [M+H] : 223.0793; Found: 223.0795.

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(cis)-Ethyl 2-(phenylsulfanyl)cyclopropane-1-carboxylate (16) -1 Rf = 0.35 (4:1 n-hexane:Et2O). IR (film)/cm 3074 (CH), 3059 (CH), 2981 (CH), 2937 1 (CH), 2906 (CH), 2874, 1728 (C=O), 1585, 1480, 1380. H NMR (400 MHz, CDCl3) d 7.37–7.34 (m, 2 H, 2 × Ph-H), 7.30–7.25 (m, 2 H, 2 × Ph-H), 7.17–7.13 (m, 1 H, Ph-H),

4.06 (q, J = 7.1 Hz, 2 H, CH2CH3), 2.70 (ddd, J = 7.8, 7.8, 6.7 Hz, 1 H, Hc), 2.25 (ddd,

J = 7.8, 7.8, 6.7 Hz, 1 H, Hd), 1.49–1.45 (m, 2 H, Ha + Hb), 1.11 (t, J = 7.1 Hz, 3 H, 13 CH3). C NMR (101 MHz, CDCl3) d 169.6 (C=O), 137.1 (Ph-C quat), 128.7 (2 × Ph-C),

127.5 (2 × Ph-C), 125.5 (Ph-C), 60.8 (CH2CH3), 22.07 (C(Hd)), 22.05 (C(Hc)), 14.1 + + (CH3), 13.2 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C12H15O2S [M+H] : 223.0793; Found: 223.0801. The observed data for (cis)-Ethyl 2-(phenylsulfanyl)cyclopropane- 1-carboxylate (IR, 1H, 13C) was consistent with that previously reported.284

These compounds display characteristic J-values which have been considered in all assignments:[9]

(trans)-Ethyl 2-(phenylsulfanyl) (cis)-Ethyl 2-(phenylsulfanyl) cyclopropane-1-carboxylate (15) cyclopropane-1-carboxylate (16)

5.6 Hz 6.9 Hz 2 CO2Et Jgem = 4.5-7.0 Hz 8.2 Hz Hc 3.6 Hz Hb 3 Hb SPh Jtrans = 4.5-7.5 Hz SPh 3 4.9 Hz J = 7.5-11.0 Hz H cis CO2Et c Ha 7.8 Hz Ha 7.8 Hz 8.8 Hz 7.8 Hz Hd Hd 5.4 Hz 6.7 Hz

Synthesis of CoII(salen)-type complex 28 via Schiff base 27

(±)-N,N’-Bis[(E)-3,5-di-tert-butylsalicylidene]-(trans)-1,2-cyclohexanediamine (27)

N N

t-Bu OH HO t-Bu

t-Bu t-Bu

3,5-Di-tert-butyl-2-hydroxybenzaldehyde (4.0 g, 17.0 mmol), ethanol (40 mL) and (±)-1,2-trans-diaminocyclohexane (1.0 mL, 1.1 g, 9.4 mmol) were stirred at reflux for

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3.5 h. The reaction mixture was cooled to rt and the mixture filtered, washing with ethanol, to give Schiff base (±)-27 (3.79 g, 81%) as a vivid yellow crystalline solid. Rf -1 = 0.76 (2:1 n-hexane:Et2O). mp = 213–216 °C. IR (pure sample)/cm 2949 (CH), 2862 1 (CH), 1630 (C=N), 1468, 1437, 1362. H NMR (400 MHz, CDCl3) d 13.70 (s, 2 H, 2 ´ N=CH), 8.29 (s, 2 H, 2 ´ OH), 7.29 (d, J = 2.5 Hz, 2 H, 2 ´ Ar-H), 6.97 (d, J = 2.5 Hz,

2 H, 2 ´ Ar-H), 3.37–3.26 (m, 2 H, 2 ´ NCH), 1.93 (d, J = 13.5 Hz, 2 H, CH2), 1.89–

1.86 (m, 2 H, CH2), 1.78–1.69 (m, 2 H, CH2), 1.56–1.43 (m, 2 H, CH2), 1.41 (s, 18 H, 13 2 ´ C(CH3)3, 1.23 (s, 18 H, 2 ´ C(CH3)3). C NMR (101 MHz, CDCl3) d 165.8 (2 ´ N=C), 158.0 (2 ´ Ar-C quat.), 139.9 (2 ´ Ar-C quat.), 136.3 (2 ´ Ar-C quat.), 126.7 (2 ´

Ar-C), 126.0 (2 ´ Ar-C), 117.8 (2 ´ Ar-C quat.), 72.4 (2 ´ NCH), 34.9 (4 ´ C(CH3)3),

33.3 (2 ´ NCH2), 31.4 (2 ´ C(CH3)3), 29.4 (2 ´ C(CH3)3), 24.3 (2 ´ NCH2CH2). HRMS + + (ES) m/z Calcd for C36H55N2O2 [M+H] : 547.4264; Found: 547.4247. Observed data (1H, 13C) was consistent with that previously reported.324

(±)-N,N’-Bis[(E)-3,5-di-tert-butylsalicylidene]-(trans)-1,2-cyclohexanediamino cobalt(II) (28)

N N Co t-Bu O O t-Bu

t-Bu t-Bu

To a 50 mL round bottomed flask were added Co(OAc)2 (0.647 g, 3.66 mmol), EtOH (30 mL) and (±)-27 (2.00 g, 3.66 mmol) and the mixture stirred at reflux for 3.5 h. The reaction mixture was allowed to cool to rt, then filtered, washing with ethanol. Recrystallisation from i-propanol gave complex (±)-28 (2.01 g, 91%) as a vivid red solid. Melting point > 250 °C. IR (pure sample)/cm-1 2947 (CH), 2913 (CH), 2864 (CH), + + 1595, 1528, 1462, 1360, 1339. HRMS (ES) m/z Calcd for C36H52N2O2 [M] : 603.3361; Found: 603.3355.

193

Synthesis of disulfides 37–40

Bis(2-methylphenyl) disulfide (37)

CH3 S S CH3

2-Methylbenzenethiol (3.8 mL, 4.0 g, 32.2 mmol, 1.0 equiv), CHCl3 (310 mL) and 1,3-dibromo-5,5-dimethylhydantoin (2.3 g, 8.05 mmol, 0.25 equiv) were stirred at rt for 1.5 h. The reaction mixture was filtered and concentrated under reduced pressure.

The residue was dissolved in EtOAc (100 mL), washed with 1.0 M KOH(aq) (250 mL) and the aqueous phase extracted with EtOAc (100 mL). The organic phases were combined, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure to give disulfide 37 (3.91 g, 99%) as a yellow crystalline solid. Rf (9:1 1 i-hexane:Et2O) = 0.55. H NMR (400 MHz, CDCl3) d 7.52–7.49 (m, 2 H, 2 ´ Ar-H), 13 7.18–7.10 (m, 6 H, 6 ´ Ar-H), 2.43 (s, 6 H, 2 ´ CH3). C NMR (101 MHz, CDCl3) d 137.4 (2 ´ Ar-C quat), 135.4 (2 ´ Ar-C quat), 130.3 (2 ´ Ar-C), 128.6 (2 ´ Ar-C), 127.3 1 13 (2 ´ Ar-C), 126.7 (2 ´ Ar-C), 20.1 (2 ´ CH3). The observed data ( H, C) was consistent with that previously reported.325

Bis(2-trifluoromethylphenyl) disulfide (38)

F F F

S S

F F F

2-(Trifluoromethyl)benzenethiol (3.7 mL, 5.0 g, 28.1 mmol, 1.0 equiv), CHCl3 (270 mL) and 1,3-dibromo-5,5-dimethylhydantoin (2.0 g, 7.02 mmol, 0.25 equiv) were stirred at rt for 3 h. The reaction mixture was filtered and concentrated under reduced pressure.

194

1 i-hexane:Et2O) = 0.43. H NMR (400 MHz, CDCl3) d 7.84 (d, J = 8.0 Hz, 2 H, 2 ´ Ar-H), 7.64, (d, J = 8.0 Hz, 2 H, 2 ´ Ar-H), 7.49 (t, J = 8.0 Hz, 2 H, 2 ´ Ar-H), 7.33 (t, J =

13 8.0 Hz, 2 H, 2 ´ Ar-H). C NMR (101 MHz, CDCl3) d 135.4 (2 ´ Ar-C-S), 132.5 (2 ´ Ar-C), 129.5 (2 ´ Ar-C), 128.5 (q, J = 31.3 Hz, 2 ´ Ar-C quat), 127.2 (2 ´ Ar-C), 126.7

1 13 (q, J = 5.1 Hz, 2 ´ Ar-C), 123.6 (q, J = 274.7 Hz, 2 ´ CF3). The observed data ( H, C) was consistent with that previously reported.326

Bis(4-chlorophenyl) disulfide (39)

S S Cl

4-Chlorobenzenethiol (4.05 g, 28.0 mmol, 1.0 equiv), CHCl3 (270 mL) and 1,3-dibromo-5,5-dimethylhydantoin (2.0 g, 7.0 mmol, 0.25 equiv) were stirred at rt for 2 h. The reaction mixture was filtered and concentrated under reduced pressure. The residue was dissolved in EtOAc (100 mL), washed with 1.0 M KOH(aq) (250 mL) and the aqueous phase extracted with EtOAc (100 mL). The organic phases were combined, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure to give disulfide 39 (3.941 g, 98%) as a yellow crystalline solid. Rf (9:1 1 i-hexane:Et2O) = 0.60. H NMR (400 MHz, CDCl3) d 7.42–7.38 (m, 4 H, 4 ´ Ar-H), 13 7.29–7.26 (m, 4 H, 4 ´ Ar-H). C NMR (101 MHz, CDCl3) d 135.2 (2 ´ Ph-C quat), 133.7 (2 ´ Ph-C quat), 129.4 (4 ´ Ph-C), 129.3 (4 ´ Ph-C). The observed data (1H, 13C) was consistent with that previously reported.327

Bis(4-trifluoromethylphenyl) disulfide (40)

F F F S S F F F

4-(Trifluoromethyl)benzenethiol (3.85 g, 28.0 mmol, 1.0 equiv), CHCl3 (270 mL) and 1,3-dibromo-5,5-dimethylhydantoin (2.0 g, 7.0 mmol, 0.25 equiv) were stirred at rt for 2 h. The reaction mixture was filtered and concentrated under reduced pressure. The

195

residue was dissolved in EtOAc (100 mL), washed with 1.0 M KOH(aq) (250 mL) and the aqueous phase extracted with EtOAc (100 mL). The organic phases were combined, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure to give disulfide 40 (4.744 g, 96%) as a cream crystalline solid. Rf (9:1 1 i-hexane:Et2O) = 0.57. H NMR (400 MHz, CDCl3) d 7.82–7.34 (m, 8 H, 8 ´ Ar-H). 13 C NMR (101 MHz, CDCl3) d 140.8 (d, J = 1.5 Hz, 4 ´ Ar-C), 129.6 (q, J = 33.3 Hz, 2 ´ Ar-C quat), 126.6 (2 ´ Ar-C-S), 126.1 (q, J = 4.4 Hz, 4 ´ Ar-C), 123.8 (q, J = 272.7 Hz, 1 13 327 2 ´ CF3). The observed data ( H, C) was consistent with that previously reported.

Synthesis of vinyl sulfides 41–45

2-Methylphenylvinyl sulfide (41)

CH3 Hb S Hc Ha

Vinyl magnesium bromide (1.0 M in THF, 2.44 mL, 2.44 mmol, 2.0 equiv) was added to a 0 °C solution of disulfide 37 (300 mg, 1.22 mmol, 1.0 equiv) in THF (10 mL) and the reaction mixture was stirred at 0 °C for 3.5 h, then rt for 1 h. The reaction mixture was concentrated under reduced pressure, dissolved in i-hexane, filtered and concentrated under reduced pressure. Purification (12 g RediSep silica cartridge,

3–10% Et2O:i-hexane, 20 column volumes) gave the vinyl sulfide 41 (65 mg, 35%) as 1 a colourless oil. H NMR (400 MHz, CDCl3) d 7.40–7.37 (m, 1 H, Ar-H), 7.24–7.12 (m,

3 H, 2 ´ Ar-H), 6.47 (dd, J = 16.5, 9.6 Hz, 1 H, Ha), 5.31 (d, J = 9.6 Hz, 1 H, Hc), 5.15 1 (d, J = 16.5 Hz, 1 H, Hb), 2.40 (s, 3 H, CH3). The observed data ( H) was consistent with that previously reported.328

196

2-Trimethylphenylvinyl sulfide (42)

F F F Hb S Hc Ha

Vinyl magnesium bromide (1.0 M in THF, 2.25 mL, 2.25 mmol, 2.0 equiv) was added to a 0 °C solution of disulfide 38 (400 mg, 1.13 mmol, 1.0 equiv) in THF (9.25 mL) and the reaction stirred at 0 °C for 3 h, then rt for 1 h. The reaction mixture was concentrated under reduced pressure and purified (150 g C18 RediSep cartridge, ammonium bicarbonate(aq):acetonitrile). The required fractions were combined and extracted with i-hexane (5 × 100 mL). The organic phases were combined, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure (in a water bath cooled to 5–10 °C) to obtain vinyl sulfide 42 (168 mg, 73%) as a light pink 1 oil. H NMR (400 MHz, CDCl3) d 7.68 (d, J = 8.0 Hz, 1 H, Ar-H), 7.49 (m, 2 H, 2 ´

Ar-H), 7.34 (m, 1 H, Ar-H), 6.50 (dd, J = 16.6, 9.6 Hz, 1 H, Ha), 5.51–5.48 (d, J =

9.6 Hz, 1 H, Hc), 5.50–5.46 (d, J = 16.6 Hz, 1 H, Hb).

4-Chlorophenylvinyl sulfide (43)

Hb S Hc H Cl a

Vinyl magnesium bromide (1.0 M in THF, 2.1 mL, 2.1 mmol, 2.0 equiv) was added to a 0 °C solution of disulfide 39 (300 mg, 1.04 mmol, 1.0 equiv) in THF (8.5 mL) and the reaction mixture stirred at 0 °C for 3 h, then room temperature for 1 h. Sat. NH4Cl(aq)

(10 mL was added and stirred for 10 min. The mixture was extracted with CH2Cl2 (2 ×

15 mL), the organic phases were combined and washed with 1.0 M KOH(aq), with the aqueous phase being washed with CH2Cl2 (15 mL). The organic phases were combined and concentrated under reduced pressure to give vinyl sulfide 43 (147 mg, 1 83%) as a pale yellow oil. H NMR (400 MHz, CDCl3) d 7.32–7.28 (m, 4 H, 4 ´ Ar-H),

6.49 (dd, J = 16.6, 9.6 Hz, 1 H, Ha), 5.39 (d, J = 9.6 Hz, 1 H, Hc), 5.35 (d, J = 16.6 Hz, 1 329 1 H, Hb). The observed data ( H) was consistent with that previously reported.

197

4-Trifluoromethylphenylvinyl sulfide (44)

Hb S Hc F Ha F F

Vinyl magnesium bromide (1.0 M in THF, 1.7 mL, 1.7 mmol, 1.5 equiv) was added to a 0 °C solution of disulfide 40 (400 mg, 1.13 mmol, 1.0 equiv) in THF (9.25 mL) and the reaction mixture stirred at 0 °C for 2.5 h, then room temperature for 2 h. Sat.

NH4Cl(aq) (10 mL) was added and stirred for 10 min. The mixture was extracted with

CH2Cl2 (2 × 20 mL), then the organic phases were combined and washed with 1.0 M

KOH(aq), with the aqueous phase being extracted with CH2Cl2 (20 mL). The organic phases were combined and concentrated under reduced pressure. Purification (24 g RediSep silica cartridge, 100% i-hexane, 20 column volumes) gave vinyl sulfide 44 1 (89 mg, 38%) as a pale yellow oil. H NMR (400 MHz, CDCl3) d 7.70–7.32 (m, 5 H, 5 ´

Ar-H), 6.55 (dd, J = 12.0, 8.0 Hz, 1 H, Ha), 5.55 (d, J = 12.0 Hz, 1 H, Hb), 5.55 (d, J = 1 8.0 Hz, 1 H, Hc). The observed data ( H) was consistent with that previously reported.330

4-Methoxyphenylvinyl sulfide (45)

Hb S Hc H MeO a

Vinyl magnesium bromide (1.0 M in THF, 2.2 mL, 2.2 mmol, 1.5 equiv) was added to a 0 °C solution of bis(4-methoxyphenyl)disulfide (400 mg, 1.44 mmol, 1.0 equiv) in THF (12 mL) and the reaction mixture stirred at 0 °C for 3.5 h, then rt for 1 h. Sat.

NH4Cl(aq) (10 mL) was added and stirred for 10 min. The mixture was extracted with

CH2Cl2 (2 × 10 mL), the organic phases combined and washed with 1.0 M KOH(aq), with the aqueous phase being extracted with CH2Cl2 (10 mL). The organic phases were combined and concentrated under reduced pressure. Purification (24 g RediSep silica cartridge, 1–3% Et2O:i-hexane, 20 column volumes) gave vinyl sulfide 45 1 (30.0 mg, 13%) as a pale yellow oil. H NMR (400 MHz, CDCl3) d 7.37 (d, J = 9.0 Hz,

2 H, 2 ´ Ar-H), 6.89 (d, J = 9.0 Hz, 2 H, 2 ´ Ar-H), 6.47 (dd, J = 16.6, 9.8 Hz, 1 H, Ha),

198

5.22 (d, J = 9.8 Hz, 1 H, Hc), 5.10 (d, J = 16.6 Hz, 1 H, Hb), 3.81 (s, 3 H, CH3). The observed data (1H) was consistent with that previously reported.329

II Synthesis of Enantiopure C2-Symmetric Co -(Salen)-Type Complexes

Complexes 28* and 67 were obtained commercially from Sigma Aldrich.

Synthesis of complex 66

2,2'-{[(1R,2R)-1,2-diphenylethane-1,2diyl]bis[azanylylidene(E)-methanyl ylidene]}bis(4,6-di-tert-butylphenol) (65)

N N

t-Bu OH HO t-Bu

t-Bu t-Bu

3,5-Di-tert-butyl-2-hydroxybenzaldehyde (600 mg, 2.56 mmol, 2.0 equiv), EtOH (20 mL) and (1R,2R)-(+)-1,2-diphenylethylenediamine (272 mg, 1.28 mmol, 1.0 equiv) were stirred at reflux for 20 h. The reaction was cooled, then filtered to give Schiff base 1 65 (500 mg, 61%) as a pale yellow solid. H NMR (400 MHz, CDCl3) d 13.60 (s, 2 H, 2 ´ N=CH), 8.40 (s, 2 H, 2 ´ Ar-H), 7.36–6.93 (m, 12 H, 2 ´ Ar-H + 10 ´ Ph-H), 4.71 13 (s, 2 H, 2 ´ CH(N)), 1.42 (s, 18 H, C(CH3)3), 1.21 (s, 18 H, C(CH3)3). C NMR

(101 MHz, CDCl3) d 167.2 (2 ´ C=N), 158.0 (2 ´ Ar-C quat), 140.0 (2 ´ Ar-C quat), 139.8 (2 ´ Ar-C quat), 136.4 (2 ´ Ar-C quat), 128.3 (4 ´ Ph-C), 128.0 (4 ´ Ph-C), 127.4 (2 ´ Ar-C), 127.1 (2 ´ Ar-C), 126.3 (2 ´ Ar-C), 117.9 (2 ´ Ar-C quat), 35.0 (2 ´ CH(N)),

1 34.0 (4´ C(CH3)3 quat), 31.4 (C(CH3)3), 29.4 (C(CH3)3). The observed data ( H) was consistent with that previously reported.331

199

N,N'-Bis[(E)-(3,5-di-tert-butyl)-2-hydroxyphenylmethylene]-[(1R,2R)-1,2- diphenylethylenediamino]cobalt(II) (66)

N N Co t-Bu O O t-Bu

t-Bu t-Bu

A mixture of Co(OAc)2 (123 mg, 0.70 mmol, 1.0 equiv), H2O (2.0 mL) and ethanol (4.0 mL) was added to a solution of 65 (450 mg, 0.70 mmol, 1.0 equiv) in toluene (4.0 mL, 0.18 M). The reaction mixture was stirred at reflux for 3 h, cooled to rt, concentrated under reduced pressure, then recrystallised from ethanol to obtain 66 (327 mg, 67%) as a vivid red solid. mp > 250 °C. IR (film)/cm-1 2951 (CH), 2904 (CH), 2867 (CH), 1589 (C=N), 1525, 1454, 1319, 1250, 1179, 787, 698. FTMS (+ p NSI) m/z + + Calcd for C44H54CoN2O2 [M] : 701.3512; Found: 701.3505. The observed data (IR) was consistent with that previously reported.201

Synthesis of complex 68

N,N′-Bis[(E)-5-tert-butyl-3-[(morpholin-4-yl)methyl]-2-hydroxybenzylidene]- [(1S,2S)-1,2-cyclohexanediamino]cobalt(II) (68)

N N Co O O

N N

O O

4-tert-Butyl-2-[({(1S,2S)-2-[(E)-({5-tert-butyl-2-hydroxy-3-[(morpholin-4yl)methyl] phenyl}methylidene)amino]cyclohexyl}imino)methyl]-6-[(morpholin-4yl)methyl]phenol

(100 mg, 0.16 mmol, 1.0 equiv), EtOH (2.0 mL) and Co(OAc)2 (28 mg, 1.0 equiv) were stirred at reflux for 17 h. The reaction mixture was cooled slowly to -78 °C and filtered

200

to give complex 68 (15 mg, 14%) as a vivid orange solid. High pH LCMS; 1.286 min, mass found: 689.4.

Synthesis of complex 69

N,N′-Bis[(E)-2,3-dihydroxybenzylidene]-[(1R,2R)-1,2-cyclohexanediamino] cobalt(II) (69)

N N Co O O

OH HO

3-({[(1R,2R)-2-{(E)-[(2,3dihydroxyphenyl)methylidene]amino}cyclohexyl]imino} methyl)benzene-1,2-diol (155 mg, 0.44 mmol, 1.0 equiv), EtOH (8 mL) and Co(OAc)2 (77 mg, 0.44 mmol, 1.0 equiv) were stirred at reflux for 17 h. The reaction mixture was cooled to rt and filtered. The filtrate was recrystallised from a solution of EtOH (30 mL),

MeOH (30 mL) and CHCl3 (5 mL) to give complex 69 (25 mg, 14%) as a brown solid. + + FTMS (+p NSI) m/z Calcd for C20H20N2O4Co [M] : 411.0750; Found: 411.0750.

Synthesis of complex 71

2-Ethoxy-6-({[(1R,2R)-2-{(E)-[(3-ethoxy-2-hydroxyphenyl)methylidene] amino}cyclohexyl]imino}methyl)phenol (70)

N N

OH HO

OEt EtO

A solution of 3-ethoxy-2-hydroxybenzaldehyde (283 mg, 1.7 mmol, 2.0 equiv) in EtOH (10 mL) was added to a solution of (1R,2R)-(–)-1,2-diaminocyclohexane (97 mg, 0.85 mmol, 1.0 equiv) in EtOH (3 mL) and the mixture was stirred at reflux for 3 h. The

201

mixture was concentrated under reduced pressure to give Schiff base 70 (342 mg, -1 98%) as a vivid yellow oil. Rf (2:1 n-hexane:Et2O) = 0.10. IR (film)/cm 2980 (CH), 1 2930 (CH), 2859 (CH), 1625 (C=N), 1462, 1244, 1077. H NMR (400 MHz, CDCl3) d 13.93 (s, 2 H, 2 ´ OH), 8.24 (s, 2 H, 2 ´ HC=N), 6.86 (dd, J = 7.8, 1.6 Hz, 2 H, 2 ´ Ar-H), 6.78 (dd, J = 7.8, 1.6 Hz, 2 H, 2 ´ Ar-H), 6.71 (t, J = 7.8 Hz, 2 H, 2 ´ Ar-H), 4.07

(q, J = 7.0 Hz, 4 H, 2 ´ CH2CH3), 3.34–3.26 (m, 2 H, 2 ´ NCH), 2.01–1.69 (m, 8 H, 4 13 ´ CH2), 1.48 (t, J = 7.0 Hz, 6 H, 2 ´ CH3). C NMR (101 MHz, CDCl3) d 164.7 (2 ´ C=N), 151.7 (2 ´ Ar-quat), 147.5 (2 ´ Ar-quat), 123.1 (2 ´ Ar-H), 118.4 (2 ´ Ar-quat),

117.8 (2 ´ Ar-H), 115.0 (2 ´ Ar-H), 72.4 (2 ´ NCH), 64.3 (2 ´ OCH2), 33.0 (2 ´ CH2), + + 24.0 (2 ´ CH2), 14.9 (2 ´ CH3). ES+ m/z Calcd for C24H31N2O4 [M-H] : 411.2284; Found: 411.2291. The observed data (1H, 13C) was consistent with that previously reported.332

N,N′-Bis[(E)-3-ethoxy-2-hydroxybenzylidene]-[(1R,2R)-1,2-cyclohexane diamino]cobalt(II) (71)

N N Co O O

OEt EtO

A mixture of Co(OAc)2 (33 mg, 0.18 mmol), H2O (1.0 mL) and ethanol (2.5 mL) was added to a solution of 70 (74 mg, 0.18 mmol) in toluene (1.5 mL, 0.12 M). The reaction mixture was refluxed for 3 h, cooled to rt, concentrated under reduced pressure, then recrystallised from CHCl3 to give 71 (74 mg, quant) as a brown solid. mp > 250 °C. IR (film)/cm-1 3250 (CH), 2980 (CH), 2935 (CH), 2864 (CH), 1635 (C=N), 1603, 1561, + + 1469, 1447, 1390, 1247, 1222. FTMS (+ p NSI) m/z Calcd for C20H20CoN2O4 [M] : 411.0750; Found: 411.0750.

202

Synthesis of complex 74

2,3-Dichloro-5-ethoxy-6-hydroxybenzaldehyde (72)

Cl O

Cl OH

OEt

3-Ethoxysalicylaldehyde (283 mg, 1.7 mmol), AcOH (6.5 mL), then N-chlorosuccinimide (481 mg, 3.6 mmol, 2.1 equiv) were added to a flask and stirred at 80 °C for 17 h. The reaction was cooled to rt, H2O (50 mL) added, and the mixture extracted with CH2Cl2 (3 ´ 40 mL). The organic phases were combined, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash chromatography (10:1 n-hexane:Et2O) gave aldehyde 72 (285 mg, 71%) as a -1 yellow crystalline solid. Rf (8:1 n-hexane:Et2O) = 0.28. IR (film)/cm 3088 (CH), 2941 1 (CH), 2899 (CH), 1639 (C=O), 1572, 1451, 1241. H NMR (400 MHz, CDCl3) d 12.33

(s, 1 H, OH), 10.41 (s, 1 H, C=O(H)), 7.11 (s, 1 H, Ar-H), 4.11 (q, J = 7.0 Hz, 2 H, CH2), 13 1.51 (t, J = 7.0 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 195.9 (C=O), 153.5 (Ar-C quat), 147.2 (Ar-C quat), 125.4 (Ar-C quat), 123.0 (Ar-C quat), 119.7 (Ar-C), 117.0

(Ar-C quat), 65.3 (CH2), 14.5 (CH3).

3,4-Dichloro-2-({[(1R,2R)-2-{(E)-[(2,3-dichloro-5-ethoxy-6-hydroxyphenyl) methylidene]amino}cyclohexyl]imino}methyl)-6-ethoxyphenol (73)

Cl N N Cl

Cl OH HO Cl

OEt EtO

Aldehyde 72 (200 mg, 0.85 mmol, 2.0 equiv), EtOH (15 mL) and (1R,2R)-(–)-1,2- diaminocyclohexane (49 mg, 0.43 mmol, 1.0 equiv) were stirred at 90 °C for 3.5 h. The reaction mixture was concentrated under reduced pressure to give Schiff base 73 1 (225 mg, 97%) as a yellow crystalline solid. Rf (EtOAc) = 0.68. H NMR (400 MHz,

CDCl3) d 15.09 (s, 2 H, 2 ´ OH), 8.64 (s, 2 H, (H)C=N), 6.84 (s, 2 H, 2 ´ Ar-H), 4.05

(q, J = 6.8 Hz, 4 H, 2 ´ CH2), 3.48–3.31 (m, 2 H, 2 ´ CH), 2.06 (m, 2 H, CH2), 1.91 (m,

203

2 H, CH2), 1.78–1.64 (m, 2 H, CH2), 1.60–1.44 (m, 2 H, CH2), 1.48 (t, J = 6.8 Hz, 6 H, 13 2 ´ CH3). C NMR (101 MHz, CDCl3) d 163.2 (C=N), 156.4 (Ar-C quat), 147.9 (Ar-C quat), 123.4 (Ar-C quat), 120.1 (Ar-C quat), 115.9 (Ar-C), 114.3 (Ar-C), 70.8 (2 ´ NCH),

64.7 (2 ´ OCH2), 32.6 (2 ´ CH2), 23.8 (2 ´ CH2), 14.6 (2 ´ CH3).

N,N'-Bis[(E)-(2,3-di-chloro)-5-ethoxy-6-hydroxyphenylmethylene]-[(1R,2R)-1,2- cyclohexanediamino]cobalt(II) (74)

Cl N N Cl Co Cl O O Cl

OEt EtO

Co(OAc)2 (48 mg, 0.27 mmol, 1.0 equiv), H2O (150 µL), EtOH (1.5 mL), toluene (1.5 mL) and 73 (150 mg, 0.27 mmol, 1.0 equiv) were stirred at 100 °C for 1 h. EtOH (1.5 mL) was added and the mixture stirred at 100 °C for 2 h. Concentration under reduced pressure followed by recrystallisation from CHCl3 gave complex 74 (89 mg, + 54%) as a brown solid. mp > 250 °C. FTMS (+ p NSI) m/z Calcd for C24H24CoN2O4Cl4 [M]+: 602.9817; Found: 602.9813.

Synthesis of complex 76

2-({[(1R,2R)-2-{(E)-[(2-hydroxy-3,5-diiodophenyl)methylidene]amino}cyclo hexyl]imino}methyl)-4,6-diiodophenol (75)

N N

I OH HO I

I I

A solution of (1R,2R)-(–)-1,2-diaminocyclohexane (97 mg, 0.85 mmol, 1.0 equiv) in EtOH (4 mL) was added to a mixture of 3,5-diiodosalicylaldehyde (636 mg, 1.7 mmol, 2.0 equiv) in EtOH (10 mL) and the mixture was stirred at reflux for 3.5 h. The mixture was cooled to rt and concentrated under reduced pressure. Recrystallisation from

204

EtOH (10 mL) gave Schiff base 75 (571 mg, 81%) as an orange crystalline solid. Rf -1 (2:1 n-hexane:Et2O) = 0.21. mp = 130–133 °C. IR (film)/cm 3059 (OH), 2931 (CH), 1 2854 (CH), 1623 (C=N), 1436, 1275, 1155, 865. H NMR (400 MHz, CDCl3) d 14.55 (s, 2 H, 2 ´ OH), 8.05 (s, 2 H, 2 ´ HC=N), 8.01 (d, J = 2.0 Hz, 2 H, 2 ´ Ar-H), 7.43 (d, J = 2.0 Hz, 2 H, 2 ´ Ar-H), 3.35 (dd, J = 8.1, 4.2 Hz, 2 H, 2 ´ NCH), 2.03–1.40 (m, 8 H, 13 4 ´ CH2). C NMR (101 MHz, CDCl3) d 163.0 (2 ´ C=N), 160.9 (2 ´ Ar-C quat), 148.8 (2 ´ Ar-C), 140.0 (2 ´ Ar-C), 119.5 (2 ´ Ar-C quat), 87.7 (2 ´ Ar-C quat), 79.3 (2 ´ Ar-C quat), 71.8 (2 ´ CH2), 32.8 (2 ´ CH2), 23.9 (2 ´ CH2). FTMS (+ p NSI) m/z Calcd for + + 1 C20H19N2O2I4 [M-H] : 826.7626; Found: 826.7631. The observed data (IR, H) was consistent with that previously reported.333

N,N'-Bis[(E)-(3,5-di-iodo)-2-hydroxyphenylmethylene]-[(1R,2R)-1,2-cyclo hexanediamino]cobalt(II) (76)

N N Co I O O I

I I

A mixture of Co(OAc)2 (33 mg, 0.18 mmol, 1.0 equiv), H2O (1.0 mL) and ethanol (2.5 mL) was added to a solution of 75 (148 mg, 0.18 mmol, 1.0 equiv) in toluene (1.5 mL). The reaction mixture was stirred at reflux for 3 h, cooled to rt, concentrated under reduced pressure, then recrystallised in 3:2 ethanol:CHCl3 (v/v) to give 76 (151 mg, 95%) as a vivid orange solid. mp > 250 °C. IR (film)/cm-1 3003 (CH), 2938 (CH), 2858 (CH), 1738, 1599, 1568, 1490, 1422, 1398, 1160, 1031. FTMS (+ p NSI) + + m/z Calcd for C20H16CoN2O2I4 [M] : 882.6717; Found: 882.6714.

205

Synthesis of 79–82 through ester hydrolysis

(trans)-2-(Phenylsulfanyl)cyclopropane-1-carboxylic acid (79)

O HO Hc H Ha d H S b

Aqueous NaOH (1.0 M, 0.55 mL, 0.55 mmol, 1.1 equiv) was added to a solution of (trans)-ethyl 2-thiophenylcyclopropane carboxylate 15 (111 mg, 0.50 mmol, 1.0 equiv) in ethanol (2.5 mL) and the solution stirred at 30 °C for 24 h. HCl(aq) (1.0 M, 10 mL) was added and the mixture was extracted with EtOAc (5 ´ 10 mL). The combined organic phases were dried (MgSO4), filtered and concentrated under reduced pressure to give carboxylic acid 79 (97 mg, quant) as a white crystalline solid. Rf = -1 0.18 (1:1 pentane:Et2O). mp = 106-110 °C. IR (film)/cm 3008 (CH), 2863 (CH), 2530, 1 1679 (C=O), 1585, 1440, 1272, 1223, 928. H NMR (400 MHz, CDCl3) d 7.37–7.29

(m, 4 H, 4 × Ph-H), 7.25–7.18 (m, 1 H, Ph-H), 2.85 (ddd, J = 8.4, 5.8, 3.5 Hz, 1 H, Hc),

1.95 (ddd, J = 8.7, 5.3, 3.5 Hz, 1 H, Hd), 1.73 (ddd, J = 8.4, 5.3, 5.0 Hz, 1 H, Hb), 1.35 13 (ddd, J = 8.7, 5.8, 5.0 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 178.3 (C=O), 136.3

(Ph-C quat), 129.0 (2 ´ Ph-C), 127.6 (2 ´ Ph-C), 126.0 (Ph-C), 24.1 (C(Hd)), 23.5 + + (C(Hc)), 17.9 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C10H9O2S [M-H] : 193.0323; Found: 193.0332.

(cis)-2-(Phenylsulfanyl)cyclopropane-1-carboxylic acid (80)

HO Hc O H Ha d H S b

Aqueous NaOH (1.0 M, 0.55 mL, 0.55 mmol, 1.1 equiv) was added to a solution of (cis)-ethyl 2-thiophenylcyclopropane carboxylate 16 (111 mg, 0.50 mmol, 1.0 equiv) in ethanol (2.5 mL) and the solution stirred at 30 °C for 24 h. HCl(aq) (1.0 M, 10 mL) was added and the mixture was extracted with EtOAc (5 ´ 10 mL). The combined organic phases were dried (MgSO4), filtered and concentrated under reduced

206

pressure to give carboxylic acid 80 (97 mg, quant) as a cream crystalline solid. Rf = -1 0.22 (1:1 pentane:Et2O). mp = 76-79 °C. IR (film)/cm 3044 (CH), 2685 (CH), 2533, 1 1688 (C=O), 1478, 1436, 1202, 902. H NMR (400 MHz, DMSO-d6) d 12.25 (br s,

1 H, CO2H), 7.36–7.29 (m, 4 H, 4 × Ph-H), 7.18–7.13 (m, 1 H, Ph-H), 2.77 (ddd, J =

8.1, 8.0, 6.4 Hz, 1 H, Hc), 2.23 (ddd, J = 8.0, 7.9, 6.3 Hz, 1 H, Hd), 1.45 (ddd, J = 8.1, 13 7.9, 5.0 Hz, 1 H, Ha), 1.13 (ddd, J = 6.4, 6.3, 5.0 Hz, 1 H, Hb). C NMR (101 MHz,

DMSO-d6) d 170.6 (C=O), 137.3 (Ph-C quat), 129.0 (2 ´ Ph-C), 126.4 (2 ´ Ph-C),

125.2 (Ph-C), 21.3 (C(Hd)), 20.9 (C(Hc)), 12.6 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for + + C10H9O2S [M-H] : 193.0323; Found: 193.0311.

(trans)-Sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate (81)

O Na O Hc H Ha d H S b

Aqueous NaOH (1.0 M, 2.9 mL, 2.9 mmol, 1.0 equiv) was added to a solution of (trans)-ethyl 2-thiophenylcyclopropane carboxylate 15 (646 mg, 2.9 mmol, 1.0 equiv) in ethanol (14.5 mL) and the solution stirred at 30 °C for 24 h. The reaction mixture was concentrated under reduced pressure to give sodium carboxylate salt 81 (622 mg, quant) as a cream solid. mp = 207-212 °C. IR (film)/cm-1 3521 (CH), 3232 (CH), 1567

1 (C=O), 1417, 1318, 1251, 955. H NMR (400 MHz, DMSO-d6) d 7.34–7.27 (m, 4 H,

4 × Ph-H), 7.15–7.10 (m, 1 H, Ph-H), 2.39 (ddd, J = 7.9, 4.9, 3.7 Hz, 1 H, Hc), 1.43

(ddd, J = 8.8, 5.5, 3.7 Hz, 1 H, Hd), 1.30 (ddd, J = 7.9, 5.5, 3.8 Hz, 1 H, Hb), 0.76 (ddd, 13 J = 8.8, 4.9, 3.8 Hz, 1 H, Ha). C NMR (101 MHz, DMSO-d6) d 174.9 (C=O), 138.4

(Ph-C quat), 128.9 (2 ´ Ph-C), 125.8 (2 ´ Ph-C), 124.8 (Ph-C), 27.2 (C(Hd)), 18.3 + + (C(Hc)), 15.0 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C10H9O2S [M-Na] : 193.0323; Found: 193.0317.

207

(cis)-Sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate (82)

Na O Hc O H Ha d H S b

Aqueous NaOH (1.0 M, 4.5 mL, 4.5 mmol, 1.0 equiv) was added to a solution of (cis)-ethyl 2-thiophenylcyclopropane carboxylate 16 (1.00 g, 4.50 mmol, 1.0 equiv) in ethanol (22.5 mL) and the solution stirred at 30 °C for 24 h. The reaction mixture was concentrated under reduced pressure to give sodium carboxylate salt 82 (0.98 g, quant) as a cream solid. mp = 236-240 °C. IR (film)/cm-1 3078 (CH), 3055 (CH), 3016 1 (CH), 1586 (C=O), 1424, 1315, 1282, 956. H NMR (400 MHz, DMSO-d6) d 7.36–7.33 (m, 2 H, 2 × Ph-H), 7.27–7.22 (m, 2 H, 2 × Ph-H), 7.09–7.05 (m, 1 H, Ph-H), 2.24 (ddd,

J = 8.2, 8.0, 5.9 Hz, 1 H, Hc), 1.77 (ddd, J = 8.2, 8.0, 6.5 Hz, 1 H, Hd), 1.10 (ddd, J = 13 8.0, 8.0, 4.0 Hz, 1 H, Ha), 0.90 (ddd, J = 6.5, 5.9, 4.0 Hz, 1 H, Hb). C NMR (101 MHz,

DMSO-d6) d 173.2 (C=O), 139.8 (Ph-C quat), 128.6 (2 ´ Ph-C), 126.3 (2 ´ Ph-C),

124.3 (Ph-C), 24.2 (C(Hd)), 19.4 (C(Hc)), 13.3 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for + + C10H9O2S [M-Na] : 193.0323; Found: 193.0319.

Synthesis of 83–90 through amide bond formation

(cis)-N-Benzyl-2-(phenylsulfanyl)cyclopropane-1-carboxamide (83)

NH Hc O H Ha d H S b

208

Diisopropylethylamine (0.27 mL, 1.50 mmol, 3.0 equiv) was added and the solution stirred for 24 h. Water (100 mL) was added and the mixture was extracted with EtOAc (5 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (Et2O) gave amide 83 (123 mg, 87%) as a white solid. Rf = -1 0.32 (Et2O). mp = 137-140 °C. IR (film)/cm 3303 (NH), 3060 (CH), 1645 (C=O), 1552, 1 1244, 687. H NMR (400 MHz, CDCl3) d 7.36–7.09 (m, 10 H, 10 × Ph-H), 6.11 (br s,

1 H, NH), 4.37 (d, J = 5.7 Hz, 2 H, PhCH2), 2.64 (ddd, J = 8.2, 7.7, 6.4 Hz, 1 H, Hc), 13 2.10 (ddd, J = 8.2, 7.7, 6.6 Hz, 1 H, Hd), 1.49–1.41 (m, 2 H, Ha + Hb). C NMR

(101 MHz, CDCl3) d 168.5 (C=O), 138.0 (Ph-C quat), 137.1 (Ph-C quat), 128.9 (2 ´ Ph-C), 128.5 (2 ´ Ph-C), 127.7 (2 ´ Ph-C), 127.34 (2 ´ Ph-C), 127.28 (Ph-C), 125.6

(Ph-C), 43.9 (PhCH2), 23.4 (C(Hd)), 21.1 (C(Hc)), 12.9 (C(Ha)(Hb)). HRMS (ES) m/z + + Calcd for C17H18NOS [M+H] : 284.1109; Found: 284.1117.

(trans)-N-Benzyl-2-(phenylsulfanyl)cyclopropane-1-carboxamide (84)

O HN Hc H Ha d H S b

HATU (183 mg, 0.48 mmol, 1.2 equiv) was added to a solution of (trans)-sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate 81 (87 mg, 0.40 mmol, 1.0 equiv) in N,N-dimethylformamide (2.0 mL) and stirred at 40 °C for 10 min. Benzylamine (53 µL, 0.48 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (0.21 mL, 1.20 mmol, 3.0 equiv) was added and the solution stirred for 24 h. Water (100 mL) was added and the mixture was extracted with CH2Cl2 (5 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (2:1 pentane:Et2O) gave amide 84 (112 mg, 99%) as a white -1 solid. Rf = 0.17 (2:1 pentane:Et2O). mp = 129-130 °C. IR (film)/cm 3287 (NH), 3092 1 (CH), 2916 (CH), 1636 (C=O), 1559, 1391, 1222, 736, 695. H NMR (400 MHz, CDCl3) d 7.39–7.24 (m, 9 H, 9 × Ph-H), 7.18–7.13 (m, 1 H, Ph-H), 6.04 (br s, 1 H, NH), 4.57 (dd, J = 14.7, 6.1 Hz, 1 H, NC(H)H), 4.41 (dd, J = 14.7, 5.4 Hz, 1 H, NC(H)H), 2.80

209

(ddd, J = 8.5, 5.5, 3.5 Hz, 1 H, Hc), 1.74 (ddd, J = 8.3, 5.5, 4.7 Hz, 1 H, Ha), 1.61 (ddd, 13 1 H, J = 8.3, 5.4, 3.5 Hz, Hd), 1.19 (ddd, J = 8.5, 5.4, 4.7 Hz, 1 H, Hb). C NMR

(101 MHz, CDCl3) d 170.6 (C=O), 138.1 (Ph-C quat), 137.4 (Ph-C quat), 128.9 (2 ´ Ph-C), 128.8 (2 ´ Ph-C), 127.8 (2 ´ Ph-C), 127.6 (Ph-C), 126.7 (2 ´ Ph-C), 125.4

(Ph-C), 43.9 (PhCH2), 26.3 (C(Hd)), 21.1 (C(Hc)), 16.5 (C(Ha)(Hb)). HRMS (ES) m/z + + Calcd for C17H18NOS [M+H] : 284.1109; Found: 284.1103.

(trans)-(Morpholin-4-yl)-2-[(phenylsulfanyl)cyclopropyl]methanone (85)

O O N Hc H Ha d H S b

HATU (183 mg, 0.48 mmol, 1.2 equiv) was added to a solution of (trans)-sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate 81 (87 mg, 0.40 mmol, 1.0 equiv) in N,N-dimethylformamide (2.0 mL) and stirred at 40 °C for 10 min. Morpholine (42 µL, 0.48 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (0.21 mL, 1.20 mmol, 3.0 equiv) was added and the solution stirred for 24 h. H2O (100 mL) was added and the mixture was extracted with EtOAc (6 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (Et2O) gave amide 85 (101 mg, 96%) as a white solid. Rf = -1 0.36 (Et2O). mp = 77-78 °C. IR (film)/cm 2962 (CH), 2893 (CH), 2856 (CH), 1629 1 (C=O), 1441, 1233, 1117, 880. H NMR (400 MHz, CDCl3) d 7.33–7.28 (m, 4 H, 4 ×

Ph-H), 7.21–7.16 (m, 1 H, Ph-H), 3.70–3.52 (m, 8 H, 2 ´ OCH2 + 2 ´ NCH2), 2.80 (ddd,

J = 8.2, 5.4, 3.6 Hz, 1 H, Hc), 1.94 (ddd, J = 8.7, 5.3, 3.6 Hz, 1 H, Hd), 1.74 (ddd, J = 13 8.2, 5.3, 4.6 Hz, 1 H, Hb), 1.22 (ddd, J = 8.7, 5.4, 4.6 Hz, 1 H, Ha). C NMR (101 MHz,

CDCl3) d 169.4 (C=O), 137.2 (Ph-C quat), 128.9 (2 ´ Ph-H), 127.3 (2 ´ Ph-H), 125.7

(Ph-H), 66.8 (OCH2), 66.7 (OCH2), 46.0 (NCH2), 42.6 (NCH2), 22.6 (C(Hd)), 22.0 + + (C(Hc)), 16.9 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C14H18NO2S [M+H] : 264.1058; Found: 264.1056.

210

(trans)-(4-Methylpiperazin-1-yl)[2-(phenylsulfanyl)cyclopropyl]methanone (86)

O N N Hc H Ha d H S b

HATU (183 mg, 0.48 mmol, 1.2 equiv) was added to a solution of (trans)-sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate 81 (87 mg, 0.40 mmol, 1.0 equiv) in N,N-dimethylformamide (2.0 mL) and stirred at 40 °C for 10 min. 1-Methylpiperazine (54 µL, 0.48 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (0.21 mL, 1.20 mmol, 3.0 equiv) was added and the solution stirred for 24 h. Water (100 mL) was added and the mixture was extracted with EtOAc (6 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:19 MeOH:CH2Cl2) gave amide 86 (106 mg, 96%) as a -1 brown gum. Rf = 0.17 (1:19 MeOH:CH2Cl2). IR (film)/cm 3078 (CH), 3005 (CH), 2938 1 (CH), 2846 (CH), 2791, 1632 (C=O), 1439, 737. H NMR (400 MHz, CDCl3) d 7.33– 7.27 (m, 4 H, 4 × Ph-H), 7.21–7.15 (m, 1 H, Ph-H), 3.76–3.70 (m, 1 H, NCH(H)), 3.63–

3.55 (m, 3 H, 3 ´ NCH(H)), 2.78 (ddd, J = 8.2, 5.4, 3.7 Hz, 1 H, Hc), 2.42–2.37 (m, 3 H,

3 ´ NCH(H)), 2.34–2.29 (m, 4 H, 1 ´ NCH(H) + NCH3), 1.98 (ddd, J = 8.8, 5.4, 3.7 Hz,

1 H, Hd), 1.72 (ddd, J = 8.2, 5.4, 4.6 Hz, 1 H, Hb), 1.20 (ddd, J = 8.8, 5.4, 4.6 Hz, 1 H, 13 Ha). C NMR (101 MHz, CDCl3) d 169.2 (C=O), 137.3 (Ph-C quat), 128.9 (2 ´ Ph-C),

127.1 (2 ´ Ph-C), 125.6 (Ph-C), 55.2 (NCH2), 54.7 (NCH2), 46.0 (CH3), 45.5 (NCH2),

42.2 (NCH2), 22.7 (C(Hd)), 21.8 (C(Hc)), 16.8 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for + + C15H21N2OS [M+H] : 277.1375; Found: 277.1374.

211

(trans)-(3,4-Dihydroquinolin-1(2H)-yl)[2-(phenylsulfanyl)cyclopropyl] methanone (87)

O N Hc H Ha d H S b

HATU (183 mg, 0.48 mmol, 1.2 equiv) was added to a solution of (trans)-sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate 81 (87 mg, 0.40 mmol, 1.0 equiv) in N,N-dimethylformamide (2.0 mL) and stirred at 40 °C for 10 min. 1,2,3,4-Tetrahydroquinoline (60 µL, 0.48 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (0.21 mL, 1.20 mmol, 3.0 equiv) was added and the solution stirred for 24 h. Water (100 mL) was added and the mixture was extracted with EtOAc (6 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried (MgSO4), filtered and concentrated under reduced pressure.

Purification by flash column chromatography (2:1 pentane:Et2O) gave amide 87 -1 (116 mg, 94%) as a yellow gum. Rf = 0.23 (2:1 pentane:Et2O). IR (film)/cm 3058 1 (CH), 2945 (CH), 2887 (CH), 1641 (C=O), 1491, 1397, 737. H NMR (400 MHz, CDCl3) d 7.35–7.27 (m, 4 H, 4 × Ar-H), 7.20–7.09 (m, 5 H, 5 × Ph-H), 3.82 (t, J = 6.6 Hz, 2 H,

CH2), 2.96 (ddd, J = 8.1, 5.5, 3.7 Hz, 1 H, Hc), 2.73 (t, J = 6.6 Hz, 2 H, CH2), 2.26 (ddd,

J = 8.8, 5.3, 3.7 Hz, 1 H, Hd), 1.96 (m, 2 H, CH2), 1.82 (ddd, J = 8.1, 5.3, 4.5 Hz, 1 H, 13 Hb), 1.17 (ddd, J = 8.8, 5.5, 4.5 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 170.6 (C=O), 138.6 (Ar-C quat), 137.1 (2 ´ Ar-C quat), 128.9 (2 ´ Ar-C), 128.5 (Ar-C), 127.6

(2 ´ Ar-C), 126.2 (Ar-C), 125.7 (Ar-C), 125.3 (Ar-C), 124.7 (Ar-C), 43.1 (NCH2), 26.8

(CH2), 24.5 (CH2), 24.1 (C(Hd)), 23.3 (C(Hc)), 18.1 (C(Ha)(Hb)). HRMS (ES) m/z Calcd + + for C19H20NOS [M+H] : 310.1266; Found: 310.1259.

212

(cis)-(Morpholin-4-yl)-2-[(phenylsulfanyl)cyclopropyl]methanone (88)

N Hc O H Ha d H S b

HATU (228 mg, 0.60 mmol, 1.2 equiv) was added to a solution of (cis)-sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate 82 (108 mg, 0.5 mmol, 1.0 equiv) in N,N-dimethylformamide (2.5 mL) and stirred at 40 °C for 10 min. Morpholine (52 µL, 0.60 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (0.27 mL, 1.50 mmol, 3.0 equiv) was added and the solution stirred for 24 h. Water (100 mL) was added and the mixture was extracted with EtOAc (5 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (EtOAc) gave amide 88 (98 mg, 74%) as a yellow gum. Rf = 0.26 (EtOAc). IR (film)/cm-1 3055 (CH), 2963 (CH), 2855 (CH), 1635 (C=O), 1437, 1 1228, 1112, 1035, 840, 739. H NMR (400 MHz, CDCl3) d 7.39–7.36 (m, 2 H, 2 × Ph-H), 7.31–7.29 (m, 2 H, 2 × Ph-H), 7.21–7.17 (m, 1 H, Ph-H), 3.74–3.58 (m, 3 H, 3 ´ C(H)H), 3.55–3.45 (m, 3 H, 3 ´ C(H)H), 3.38–3.28 (m, 2 H, 2 ´ C(H)H), 2.76 (ddd,

J = 8.1, 8.0, 5.9 Hz, 1 H, Hc), 2.18 (ddd, J = 8.0, 8.0, 6.2 Hz, 1 H, Hd), 1.61 (ddd, J = 13 6.2, 5.9, 5.5 Hz, 1 H, Hb), 1.43 (ddd, J = 8.1, 8.0, 5.5 Hz, 1 H, Ha). C NMR (101 MHz,

CDCl3) d 166.5 (C=O), 137.0 (Ph-C quat), 128.8 (2 ´ Ph-C), 128.4 (2 ´ Ph-C), 126.0

(Ph-C), 66.8 (OCH2), 66.4 (OCH2), 45.7 (NCH2), 42.3 (NCH2), 21.5 (C(Hd)), 20.9 + + (C(Hc)), 12.8 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C14H18NO2S [M+H] : 264.1058; Found: 264.1058.

213

(cis)-(4-Methylpiperazin-1-yl)[2-(phenylsulfanyl)cyclopropyl]methanone (89)

N Hc O H Ha d H S b

HATU (228 mg, 0.60 mmol, 1.2 equiv) was added to a solution of (cis)-sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate 82 (108 mg, 0.50 mmol, 1.0 equiv) in N,N-dimethylformamide (2.5 mL) and stirred at 40 °C for 10 min. 1-Methylpiperazine (67 µL, 0.60 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (0.27 mL, 1.50 mmol, 3.0 equiv) was added and the solution stirred for 24 h. Water (100 mL) was added and the mixture was extracted with EtOAc (5 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:19 MeOH:CH2Cl2) gave amide 89 (125 mg, 90%) as a -1 brown gum. Rf = 0.08 (1:19 MeOH:CH2Cl2). IR (film)/cm 3004 (CH), 2937 (CH), 2793 1 (CH), 1635 (C=O), 1438, 1291, 1225, 1001, 739. H NMR (400 MHz, CDCl3) d 7.38– 7.36 (m, 2 H, 2 × Ph-H), 7.30–7.26 (m, 2 H, 2 × Ph-H), 7.19–7.15 (m, 1 H, Ph-H), 3.72–3.66 (m, 1 H, NC(H)H), 3.59–3.52 (m, 2 H, 2 ´ NC(H)H), 3.41–3.36 (m, 1 H,

NCH(H)), 2.74 (ddd, J = 8.0, 8.2, 5.9 Hz, 1 H, Hc), 2.44–2.31 (m, 2 H, 2 ´ NCH(H)),

2.31–2.24 (m, 1 H, NCH(H)), 2.26 (s, 3 H, CH3), 2.20 (ddd, J = 8.1, 8.0,

6.1 Hz, 1 H, Hd), 2.12 (m, 1 H, NCH(H)), 1.59 (ddd, J = 6.1, 5.9, 5.5 Hz, 1 H, Hb), 1.41 13 (ddd, J = 8.2, 8.1, 5.5 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 166.2 (C=O), 137.1

(Ph-C quat), 128.8 (2 ´ Ph-C), 128.4 (2 ´ Ph-C), 125.9 (Ph-C), 54.9 (NCH2), 54.6

(NCH2), 46.0 (CH3), 45.3 (NCH2), 41.9 (NCH2), 21.6 (C(Hd)), 20.9 (C(Hc)), 12.9 + + (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C15H21N2OS [M+H] : 277.1375; Found: 277.1371.

214

(cis)-(3,4-Dihydroquinolin-1(2H)-yl)[2-(phenylsulfanyl)cyclopropyl]methanone (90)

N Hc O H Ha d H S b

HATU (228 mg, 0.60 mmol, 1.2 equiv) was added to a solution of (cis)-sodium 2-(phenylsulfanyl)cyclopropane-1-carboxylate 82 (108 mg, 0.50 mmol, 1.0 equiv) in N,N-dimethylformamide (2.5 mL) and stirred at 40 °C for 10 min. 1,2,3,4-Tetrahydroquinoline (75 µL, 0.60 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (0.27 mL, 1.50 mmol, 3.0 equiv) was added and the solution stirred for 24 h. Water (100 mL) was added and the mixture was extracted with EtOAc (5 ´ 20 mL). The combined organic phases were washed with brine (30 mL), dried (MgSO4), filtered and concentrated under reduced pressure.

Purification by flash column chromatography (2:1 pentane:Et2O) gave amide 90 -1 (122 mg, 79%) as a yellow gum. Rf = 0.15 (2:1 pentane:Et2O). IR (film)/cm 3004 (CH), 2937 (CH), 2793 (CH), 1635 (C=O), 1438, 1291, 1225, 1001, 739. 1H NMR

(400 MHz, CDCl3) d 7.42–7.40 (m, 2 H, 2 ´ Ph-H), 7.29–7.26 (m, 2 H, 2 ´ Ph-H), 7.19– 7.07 (m, 5 H, 5 ´ Ar-H), 4.14–4.12 (m 1 H, 1 ´ CH(H)), 3.57–3.54 (m, 1 H, CH(H)),

2.68–2.64 (m, 3 H, 2 ´ CH(H) + Hc), 2.42 (ddd, J = 8.0, 8.0, 6.3 Hz, 1 H, Hd), 2.05– 1.98 (m, 1 H, CH(H)), 1.85–1.75 (m, 1 H, CH(H)), 1.70 (ddd, J = 6.3, 6.2, 5.1 Hz, 1 H, 13 Hb), 1.44 (ddd, J = 8.0, 8.0, 5.1 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 167.8 (C=O), 138.9 (Ar-C quat), 137.1 (2 ´ Ar-C quat), 128.82 (2 ´ Ph-C), 128.78 (2 ´ Ph-C),

128.5 (Ar-C), 126.0 (Ar-C), 125.9 (Ar-C), 125.1 (2 ´ Ar-C), 124.5 (Ar-C), 43.4 (NCH2),

26.9 (CH2), 24.0 (CH2), 23.8 (C(Hc)), 22.6 (C(Hd)), 15.0 (C(Ha)(Hb)). HRMS (ES) m/z + + Calcd for C19H20NOS [M+H] : 310.1266; Found: 310.1267.

215

Synthesis of 91–92 through reduction

(trans)-[2-(Phenylsulfanyl)cyclopropyl]methanol (91)

HO Hc H Ha d H S b

Lithium aluminium tetrahydride (1.0 M in THF, 1.0 mL, 1.0 mmol, 2.5 equiv) was added dropwise over 5 min to a 0 °C solution of (trans)-ethyl 2-thiophenylcyclopropane carboxylate 15 (89 mg, 0.40 mmol, 1.0 equiv) in THF (0.5 mL) and the solution stirred at 0 °C for 10 min. The solution was warmed to 25 °C and stirred for 3 h. The reaction mixture was cooled to 0 °C, EtOAc (5 ml) was added and the mixture stirred for 15 min. The mixture was warmed to 25 °C, sat. aq. potassium sodium tartrate (5.0 mL) was added and the mixture stirred for 1 h. The organic phase was separated, and the aqueous phase extracted with Et2O (6 ´ 10 mL). The combined organic phases were washed with brine (20 mL), dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (2:1 pentane:Et2O) gave -1 alcohol 91 (63 mg, 87%) as a yellow oil. Rf = 0.13 (2:1 pentane:Et2O). IR (film)/cm 3340 (OH), 3059 (CH), 3004 (CH), 2923 (CH), 2873 (CH), 1584, 1480, 1271, 1025, 1 738, 690. H NMR (400 MHz, CDCl3) d 7.41–7.39 (m, 2 H, 2 × Ph-H), 7.32–7.28 (m, 2 H, 2 × Ph-H), 7.18–7.14 (m, 1 H, Ph-H), 3.73 (dd, J = 11.4, 6.1 Hz, 1 H, OCH(H)),

3.56 (dd, J = 11.4, 7.1 Hz, 1 H, OCH(H)), 2.17 (ddd, J = 8.0, 4.3, 4.5 Hz, 1 H, Hc),

1.48–1.40 (m, 1 H, Hd), 1.05 (ddd, J = 8.0, 5.5, 4.8 Hz, 1 H, Hb), 0.95 (ddd, J = 8.9, 13 4.8, 4.5 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 138.2 (Ph-C quat), 128.8 (2 ´

Ph-C), 126.8 (2 ´ Ph-C), 125.3 (Ph-C), 65.2 (OCH2), 24.9 (C(Hc)), 17.4 (C(Hd)), 13.2 + + (C(Ha)(Hb)). HRMS (EI) m/z Calcd for C10H12OS [M] : 180.0609; Found: 180.0599.

216

(cis)-[2-(Phenylsulfanyl)cyclopropyl]methanol (92)

HO Hc H Ha d H S b

Lithium aluminium tetrahydride (1.0 M in THF, 1.0 mL, 1.0 mmol, 2.5 equiv) was added dropwise over 5 min to a solution of (cis)-ethyl 2-thiophenylcyclopropane carboxylate 16 (89 mg, 0.40 mmol, 1.0 equiv) in THF (0.5 mL) at 0 °C. The solution was stirred at 0 °C for 10 min then 25 °C for 3 h. The reaction mixture was cooled to 0 °C, EtOAc (5 ml) was added and the mixture stirred for 15 min. The mixture was warmed to 25 °C, sat. aq. potassium sodium tartrate (5.0 mL) was added and the mixture stirred for 1 h.

The organic phase was separated, and the aqueous phase extracted with Et2O (6 ´ 10 mL). The combined organic phases were washed with brine (20 mL), dried

(MgSO4), filtered and concentrated under reduced pressure to give cyclopropane 92 -1 (63 mg, 87%) as a colourless oil. Rf = 0.40 (1:1 pentane:Et2O). IR (film)/cm 3245 (OH), 3069 (CH), 3008 (CH), 2928 (CH), 2869 (CH), 1582, 1478, 1438, 1056, 1022, 1 733. H NMR (400 MHz, CDCl3) d 7.41–7.38 (m, 2 H, 2 × Ph-H), 7.33–7.29 (m, 2 H, 2 × Ph-H), 7.19–7.14 (m, 1 H, Ph-H), 3.87 (dd, J = 11.7, 4.4 Hz, 1 H, OCH(H)), 3.69

(dd, J = 11.7, 8.6 Hz, 1 H, OCH(H)), 2.48 (ddd, J = 8.0, 7.1, 5.1 Hz, 1 H, Hc), 1.71–

1.62 (m, 1 H, Hd), 1.28 (ddd, J = 8.4, 8.0, 5.5 Hz, 1 H, Ha), 0.61 (ddd, J = 5.5, 5.3, 13 5.1 Hz, 1 H, Hb). C NMR (101 MHz, CDCl3) d 138.2 (Ph-C quat), 129.0 (2 ´ Ph-C),

126.4 (2 ´ Ph-C), 125.4 (Ph-C), 62.5 (OCH2), 21.2 (C(Hd)), 18.1 (C(Hc)), 10.9 + + (C(Ha)(Hb)). HRMS (EI) m/z Calcd for C10H10S [M-H2O] : 162.0503; Found: 162.0507.

217

Synthesis of 93 through esterification

(cis)-Phenyl-2-(phenylsulfanyl)cyclopropane-1-carboxylate (93)

O Hc O H Ha d H S b

Phenol (485 mg, 5.15 mmol, 2.0 equiv), di-tert-butyl dicarbonate (590 µL, 2.57 mmol,

1.0 equiv), MgCl2 (20 mg, 0.26 mmol, 0.1 equiv), MeCN (0.5 mL) and (cis)-2-(phenylsulfanyl)cyclopropane-1-carboxylic acid 80 (500 mg, 2.57 mmol,

1.0 equiv) were stirred at 25 °C for 15 h. H2O (30 mL) was added and the mixture was extracted with EtOAc (3 ´ 20 mL). The organic phases were combined, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (19:1 pentane:EtOAc) gave ester 93 (515 mg, 74%) as a white 1 crystalline solid. Rf = 0.24 (19:1 pentane:EtOAc). H NMR (400 MHz, CDCl3) d 7.50–7.41 (m, 2 H, 2 × PhH), 7.39–7.25 (m, 4 H, 4 × Ph-H), 7.24–7.14 (m, 2 H, 2 ×

Ph-H), 6.85–6.75 (m, 2 H, 2 × Ph-H), 2.90 (q, J = 7.3 Hz, 1 H, Hc), 2.54 (q, J = 7.3 Hz, 13 1 H, Hd), 1.62 (m, 2 H, Ha + Hb). C NMR (101 MHz, CDCl3) d 168.2 (C=O), 150.6 (Ph-C quat.), 137.0 (Ph-C quat.), 129.2 (2 × Ph-C), 128.9 (2 × Ph-C), 127.4 (2 × Ph-C),

125.68 (Ph-C), 125.67 (Ph-C), 121.5 (2 × Ph-C), 22.8 (C(Hc)), 22.3 (C(Hd)), 13.6 + + (C(Ha)(Hb)). HRMS (EI) m/z Calcd for C16H14O2S [M] : 270.0715; Found: 270.0710.

218

Synthesis of 94–97 through sulfide oxidation

(trans)-Ethyl-2-(benzenesulfonyl)cyclopropane-1-carboxylate (94)

O O Hc H Ha d H S b O O mCPBA (62 mg, 0.36 mmol, 2.5 equiv) was added to a solution of (trans)-ethyl

2-thiophenylcyclopropane carboxylate 15 (32 mg, 0.14 mmol, 1.0 equiv) in CH2Cl2

(5.0 mL) and the mixture stirred at 25 °C for 24 h. Water (15 mL) and sat. aq. NaHCO3

(15 mL) were added and the mixture was extracted with CH2Cl2 (3 × 15 mL). The combined organic phases were washed with brine (15 mL), dried (MgSO4), filtered and concentrated under reduced pressure to give sulfone 94 (39 mg, quant.) as a pale -1 yellow crystalline solid. Rf = 0.45 (1:2 n-hexane:Et2O). mp = 53-56 °C. IR (film)/cm 3074 (CH), 3041 (CH), 2991 (CH), 2964 (CH), 2906 (CH), 1721 (C=O), 1449, 1306 1 (S=O), 1147 (S=O). H NMR (400 MHz, CDCl3) d 7.93–7.90 (m, 2 H, 2 × Ph-H), 7.68 (t, J = 7.5 Hz, 1 H, Ph-H), 7.59 (t, J = 7.5 Hz, 2 H, 2 × Ph-H), 4.13 (q, J = 7.1 Hz, 2 H,

CH2CH3), 2.98 (ddd, J = 8.8, 5.9, 4.1 Hz, 1 H, Hc), 2.52 (ddd, J = 9.7, 5.6, 4.1 Hz, 1 H,

Hd), 1.73 (ddd, J = 9.7, 5.9, 5.6 Hz, 1 H, Ha), 1.55 (ddd, J = 8.8, 5.6, 5.6 Hz, 1 H, Hb), 13 1.25 (t, J = 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 170.2 (C=O), 139.7 (Ph-C quat.), 133.9 (Ph-C), 129.4 (2 × Ph-C), 127.7 (2 × Ph-C), 61.6 (CH2), 40.3 (C(Hc)), + + 20.1 (C(Hd)), 14.0 (CH3), 13.3 (C(Ha)(Hb)). HRMS (EI) m/z Calcd for C12H14O4S [M] : 254.0613; Found: 254.0619.

(cis)-Ethyl-2-(benzenesulfonyl)cyclopropane-1-carboxylate (95)

O Hc O H Ha d H S b O O

mCPBA (56 mg, 0.33 mmol, 2.5 equiv) was added to a solution of (cis)-ethyl

2-thiophenylcyclopropane carboxylate 16 (29 mg, 0.13 mmol, 1.0 equiv) in CH2Cl2

219

(5.0 mL) and the mixture stirred at 25 °C for 25 h. H2O (10 mL) and sat. aq. NaHCO3

(15 mL) were added and the mixture was extracted with CH2Cl2 (3 × 15 mL). The combined organic phases were washed with brine (20 mL), dried (MgSO4), filtered and concentrated under reduced pressure to give sulfone 95 (33 mg, quant.) as a pale -1 yellow crystalline solid. Rf = 0.33 (1:2 n-hexane:Et2O). mp = 100–102 °C. IR (film)/cm 3098 (CH), 3063 (CH), 3042 (CH), 2984 (CH), 2937 (CH), 2910 (CH), 1733, 1447, 1 1324 S=O), 1150 (S=O). H NMR (400 MHz, CDCl3) d 7.95–7.93 (m, 2 H, 2 × Ph-H),

7.68–7.64 (m, 1 H, Ph-H), 7.59–7.55 (m, 2 H, 2 × Ph-H), 4.28–4.14 (m, 2 H, CH2CH3),

2.81 (ddd, J = 8.8, 8.5, 6.5 Hz, 1 H, Hc), 2.25 (ddd, J = 8.5, 8.5, 7.5 Hz, 1 H, Hd), 2.08

(ddd, J = 7.5, 6.5, 6.1 Hz, 1 H, Hb), 1.45 (ddd, J = 8.8, 8.5, 6.1 Hz, 1 H, Ha), 1.29 (t, 13 J = 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) 166.9 (C=O), 140.4 (Ph-C quat.),

133.6 (Ph-C), 129.1 (2 × Ph-C), 127.7 (2 × Ph-C), 61.8 (CH2), 39.6 (C(Hc)), 23.5 + + (C(Hd)), 13.9 (CH3), 10.4 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C12H15O4S [M+H] : 255.0691; Found: 255.0694.

(trans)-Ethyl 2-(benzenesulfinyl)cyclopropane-1-carboxylate (96)

O O Hc H Ha d Hb S O

mCPBA (2.40 g, 13.9 mmol, 1.05 equiv) was added portionwise (3 ´ 0.80 g over 30 min) to a solution of (trans)-ethyl 2-(phenylsulfanyl)cyclopropane-1-carboxylate 15

(2.95 g, 13.3 mmol, 1.0 equiv) in CH2Cl2 (133 mL) at 0 °C. The reaction was stirred at 0 °C for 2 h, then aqueous KOH (3.0 M, 50 mL) was added and the phases separated.

The aqueous phase was extracted with CH2Cl2 (5 ´ 50 mL), then the organic phases were combined, washed with brine (50 mL), dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:1 to 1:2 n-hexane:Et2O) afforded a yellow oil which was dissolved in CH2Cl2, dried (MgSO4), filtered and concentrated under reduced pressure to give sulfoxides 96 (2.91 g, 92%, -1 dr = 53:47) as a pale yellow oil. Rf = 0.24 (1:2 n-hexane:Et2O). IR (film)/cm 3094 (CH), 3055 (CH), 2982 (CH), 2941 (CH), 2910 (CH), 1726 (C=O), 1444, 1381, 1258, 1182, 1048 (S-O).

220

1 Major diastereoisomer: H NMR (400 MHz, CDCl3) d 7.67–7.61 (m, 2 H, 2 × Ph-H),

7.57–7.52 (m, 3 H, 3 × Ph-H), 4.16 (dq, J = 7.1, 1.3 Hz, 2 H, CH2CH3), 2.75–2.68 (m,

1 H, Hc), 2.21 (ddd, J = 9.4, 5.6, 4.2 Hz, 1 H, Hd), 1.69 (ddd, J = 9.4, 6.0, 5.2 Hz, 1 H, 13 Ha), 1.34 (ddd, J = 8.5, 5.6, 5.2 Hz, 1 H, Hb), 1.27 (t, J = 7.1 Hz, 3 H, CH3). C NMR

(101 MHz, CDCl3) d 171.5 (C=O), 143.8 (Ph-C quat), 131.4 (Ph-C), 129.3 (2 × Ph-C),

123.9 (2 × Ph-C), 61.3 (CH2CH3), 40.6 (C(Hc)), 18.2 (C(Hd)), 14.1 (CH3), 8.1

(C(Ha)(Hb)). 1 Minor diastereoisomer H NMR (400 MHz, CDCl3) d 7.69–7.61 (m, 2 H, 2 × Ph-H),

7.57–7.52 (m, 3 H, 3 × Ph-H), 4.07 (t, J = 7.1 Hz, 2 H, CH2CH3), 2.75–2.68 (m, 1 H,

Hc), 2.40 (ddd, J = 9.1, 5.7, 4.1 Hz, 1 H, Hd), 1.57 (ddd, J = 8.9, 5.7, 5.2 Hz, 1 H, Hb), 13 1.51 (ddd, J = 9.1, 6.2, 5.2 Hz, 1 H, Ha), 1.20 (t, J = 7.1 Hz, 3 H, CH3). C NMR

(101 MHz, CDCl3) d 171.4 (C=O), 143.9 (Ph-C quat), 131.3 (Ph-C), 129.3 (2 × Ph-C),

123.9 (2 × Ph-C), 61.2 (CH2CH3), 41.4 (C(Hc)), 15.8 (C(Hd)), 14.1 (CH3), 11.7

(C(Ha)(Hb)). + + HRMS (ES) m/z Calcd for C12H15O3S [M+H] : 239.0742; Found: 239.0731.

(cis)-Ethyl-2-(benzenesulfinyl)cyclopropane-1-carboxylate (97)

O Hc O H Ha d Hb S O

mCPBA (1.21 g, 7.03 mmol, 1.05 equiv) was added portionwise (3 ´ 0.40 g over 30 min) to a solution of (cis)-ethyl 2-thiophenylcyclopropane carboxylate 16

(1.49 g, 6.69 mmol, 1.0 equiv) in CH2Cl2 (67 mL) at 0 °C. The reaction was stirred at 0 °C for 3 h then warmed to 25 °C for 16 h 30 min. Aqueous KOH (3.0 M, 50 mL) was added and the phases separated. The aqueous phase was extracted with CH2Cl2 (5 ´ 30 mL), then the organic phases were combined, washed with brine (50 mL), dried (MgSO4), filtered and concentrated under reduced pressure to give sulfoxides 97 (1.56 g, 98%, dr = 75:25) as a pale yellow oil. IR (film)/cm-1 3059 (CH), 2983 (CH), 2941 (CH), 1725 (C=O), 1444, 1382, 1188, 1040 (S-O).

221

1 Major diastereoisomer: Rf = 0.23 (Et2O). H NMR (400 MHz, CDCl3) d 7.68–7.64 (m,

2 H, 2 × Ph-H), 7.57–7.50 (m, 3 H, 3 × Ph-H), 4.23 (dt, J = 7.1, 0.7 Hz, 2 H, CH2CH3),

2.61 (ddd, J = 8.4, 8.2, 6.7 Hz, 1 H, Hc), 2.13 (ddd, J = 8.4, 8.2, 6.5 Hz, 1 H, Hd), 2.07

(ddd, J = 6.7, 6.5, 5.6 Hz, 1 H, Hb), 1.63 (ddd, J = 8.2, 8.2, 5.6 Hz, 1 H, Ha), 1.30 (t, 13 J = 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 170.0 (C=O), 145.1 (Ph-C quat.),

131.2 (Ph-C), 129.3 (2 × Ph-C), 124.0 (2 × Ph-C), 61.5 (CH2CH3), 43.3 (C(Hc)), 21.2

(C(Hd)), 14.2 (CH3), 14.1 (C(Ha)(Hb)). 1 Minor diastereoisomer: Rf = 0.31 (Et2O). H NMR (400 MHz, CDCl3) d 7.76–7.73 (m,

2 H, 2 × Ph-H), 7.57–7.50 (m, 3 H, 3 × Ph-H), 4.31 (dt, J = 7.1, 4.5 Hz, 2 H, CH2CH3),

2.68 (ddd, J = 8.8, 8.0, 6.5 Hz, 1 H, Hc), 2.31 (ddd, J = 8.0, 8.0, 6.4 Hz, 1 H, Hd), 1.75

(ddd, J = 6.5, 6.4, 5.7 Hz, 1 H, Hb), 1.38 (ddd, J = 8.8, 8.0, 5.7 Hz, 1 H, Ha), 1.35 (t, 13 J = 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 170.1 (C=O), 145.2 (Ph-C quat),

131.0 (Ph-C), 129.3 (2 × Ph-C), 124.0 (2 × Ph-C), 61.7 (CH2CH3), 44.3 (C(Hc)), 20.9

(C(Hd)), 13.6 (CH3), 11.8 (C(Ha)(Hb)). + + HRMS (ES) m/z Calcd for C12H15O3S [M+H] : 239.0742; Found: 239.0754.

Synthesis of 106–119 through sulfoxide–magnesium exchange, electrophilic trapping

(trans)-Ethyl-2-iodocyclopropanecarboxylate (106)

O O Hc

Hd Ha I Hb

i-PrMgCl (0.32 mL, 1.87 M in THF, 0.60 mmol, 1.5 equiv) was added to a −78 °C solution of (trans)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 96 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. A solution of I2 (203 mg, 0.80 mmol, 2.0 equiv) in THF (0.5 mL) was added and the reaction stirred at −78 °C for 1 h. The reaction mixture was warmed to rt, sat. aq NH4Cl (5 mL) added and the mixture was stirred for 5 min. Water (10 mL) was added and the mixture was extracted with CH2Cl2 (3 × 30 mL). The combined organic phases were washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure.

Purification by flash column chromatography (100% n-hexane to 10:1 n-hexane:Et2O)

222

gave cyclopropane 106 (79 mg, 82%) as a yellow oil. IR (film)/cm-1 2981 (CH), 1721 1 (C=O), 1396, 1376, 1174, 1033. H NMR (400 MHz, CDCl3) d 4.15 (q, J = 7.1 Hz, 2 H,

CH2CH3), 2.77 (ddd, J = 8.2, 5.6, 3.7 Hz, 1 H, Hd), 1.97 (ddd, J = 9.0, 5.6, 3.7 Hz,

1 H, Hc), 1.63 (ddd, J = 8.2, 5.6, 5.6 Hz, 1 H, Ha), 1.32-1.24 (m, 1 H, Hb), 1.27 (t, J = 13 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 171.9 (C=O), 61.1 (CH2CH3), 24.6 + (C(Hc)), 19.6 (C(Ha)(Hb)), 14.2 (CH3), -17.1 (C(Hd)). HRMS (EI) m/z Calcd for C6H9O2I [M]+: 239.9647; Found: 239.9651.

(trans)-Ethyl 2-[cyclopentyl(hydroxyl)methyl]cyclopropane-1-carboxylate (108)

O O Hc H Ha d Hb HO

Purification by flash column chromatography (2:1 pentane:Et2O) gave cyclopropane 108 as a mixture of two diastereoisomers (dr = 56:44, 60 mg, 71%) as a colourless oil. -1 Rf = 0.16 (2:1 pentane:Et2O). IR (film)/cm 3450 (OH), 2952 (CH), 2911 (CH), 2869 (CH), 1724 (C=O), 1703 (C=O), 1176. 1 Major diastereoisomer: H NMR (400 MHz, CDCl3) d 4.14-4.08 (m, 2 H, OCH2CH3),

2.94 (dd, J = 7.3, 7.3 Hz, 1 H, CH(OH)), 2.06-1.93 (m, 1 H, CH(CH2)2), 1.84-1.73 (m,

2 H, CHCH2CH2), 1.64-1.54 (m, 4 H, CH(CH2)2), 1.67-1.55 (m, 1 H, Hd), 1.60-1.54

(m, 1 H, Hc), 1.41-1.30 (m, 2 H, CHCH2CH2), 1.24 (t, J = 7.2 Hz, 3 H, CH3), 1.25-1.17 13 (m, 1 H, Hb), 0.92-0.87 (m, 1 H, Ha). C NMR (101 MHz, CDCl3) d 174.2 (C=O), 77.2

(CH(OH)), 60.5 (CH2CH3), 46.7 (CH(CH2)2), 28.9 (CH2), 28.6 (CH2), 28.0 (C(Hc)), 25.5

(CH2), 25.2 (CH2), 17.4 (C(Hd)), 14.2 (CH3), 13.2 (C(Ha)(Hb)).

223

1 Minor diastereoisomer: H NMR (400 MHz, CDCl3) d 4.14-4.08 (m, 2 H, OCH2CH3),

3.07 (dd, J = 7.1, 7.1 Hz, 1 H, CH(OH)), 2.06-1.93 (m, 1 H, CH(CH2)2), 1.84-1.73 (m,

2 H, CHCH2CH2), 1.64-1.54 (m, 4 H, CH(CH2)2), 1.67-1.55 (m, 1 H, Hd), 1.60-1.54

(m, 1 H, Hc), 1.41-1.30 (m, 2 H, CHCH2CH2), 1.24 (t, J = 7.2 Hz, 3 H, CH3), 1.14-1.08 13 (m, 1 H, Hb), 0.96-0.92 (m, 1 H, Ha). C NMR (101 MHz, CDCl3) d 174.0 (C=O), 76.4

(CH(OH)), 60.5 (CH2CH3), 46.9 (CH(CH2)2), 28.9 (CH2), 28.8 (CH2), 27.2 (C(Hc)), 25.5

(CH2), 25.2 (CH2), 18.3 (C(Hd)), 14.2 (CH3), 11.4 (C(Ha)(Hb)). + + HRMS (ES) m/z Calcd for C12H19O2 [M-OH] : 195.1385; Found: 195.1386.

(trans)-Ethyl 2-(hydroxy(phenyl)methyl)cyclopropane-1-carboxylate (109)

O O Hc H Ha d Hb HO

0 °C for 1 h. The reaction was warmed to rt, sat. aq NH4Cl (5 mL) added and the mixture was stirred for 5 min. H2O (10 mL) was added and the mixture was extracted with CH2Cl2 (3 × 30 mL). The combined organic phases were washed with brine, dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (10:1 n-hexane:Et2O) gave cyclopropane 109 as a mixture of two diastereoisomers (dr = 61:39, 83 mg, 94%) as a colourless oil. Rf = 0.16 (2:1 -1 n-hexane:Et2O). IR (film)/cm 3458 (OH), 2982 (CH), 1722 (C=O), 1703 (C=O), 1180. 1 Major diastereoisomer: H NMR (400 MHz, CDCl3) d 7.40–7.28 (m, 5 H, 5 ´ Ph-H),

4.21 (d, J = 7.3 Hz, 1 H, CH(OH)), 4.16–4.02 (m, 2 H, CH2CH3), 2.56 (br s, 1 H, OH),

1.86–1.78 (m, 1 H, Hd), 1.81 (ddd, J = 8.5, 4.3, 4.3 Hz, 1 H, Hc), 1.25 (t, J = 7.1 Hz, 13 3 H, CH3), 1.24–1.18 (m, 1 H, Ha), 0.97 (ddd, J = 8.5, 6.4, 4.5 Hz, 1H, Hb). C NMR

(101 MHz, CDCl3) d 173.7 (C=O), 142.8 (Ph-C quat), 128.5 (2 ´ Ph-C), 127.83 (Ph-C),

126.00 (2 ´ Ph-C), 75.6 (CH(OH)), 60.6 (CH2CH3), 29.2 (C(Hd)), 18.8 (C(Hc)), 14.1

(CH3), 12.5 (C(Ha)(Hb)).

224

1 Minor diastereoisomer: H NMR (400 MHz, CDCl3) d 7.40–7.28 (m, 5 H, 5 ´ Ph-H),

4.47 (d, J = 6.0 Hz, 1 H, CH(OH)), 4.16–4.02 (m, 2 H, CH2CH3), 2.45 (br s, 1 H, OH),

1.89–1.78 (m, 1 H, Hd), 1.71 (ddd, J = 8.8, 4.6, 4.6 Hz, 1 H, Hc), 1.24–1.18 (m, 1 H, 13 Ha), 1.22 (t, J = 7.1 Hz, 3 H, CH3), 1.10 (ddd, J = 8.8, 6.4, 4.2 Hz, 1 H, Hb). C NMR

(101 MHz, CDCl3) d 173.8 (C=O), 142.8 (Ph-C quat), 128.4 (2 ´ Ph-C), 127.78 (Ph-C),

126.03 (2 ´ Ph-C), 73.9 (CH(OH)), 60.5 (CH2CH3), 28.4 (C(Hd)), 17.6 (C(Hc)), 14.1

(CH3), 12.2 (C(Ha)(Hb)). + + HRMS (ES) m/z Calcd for C15H20NO3 [M+H+CH3CN adduct] : 262.1443; Found: 262.1447. The observed data (IR, 1H, 13C) was consistent with that previously reported.334

(trans)-Ethyl 2-[hydroxy(pyridine-3-yl)methyl]cyclopropane-1-carboxylate (110)

O O Hc Hf Hg H Ha d Hb Hh HO N He

i-PrMgCl (0.32 mL, 1.87 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (trans)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 96 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. 3-Pyridinecarboxaldehyde (75 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 1 h. The reaction was warmed to rt, sat. aq NH4Cl (5 mL) added and the mixture stirred for 5 min. H2O (10 mL) was added and the mixture was extracted with CH2Cl2 (6 × 20 mL) then EtOAc (6 ´ 20 mL). The combined organic phases were concentrated under reduced pressure, dissolved in CH2Cl2, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (4:1 EtOAc:toluene) gave cyclopropane 110 as a mixture of two diastereoisomers (dr = 52:48, 80 mg, 90%) as a white oil. Rf = 0.26 (4:1 EtOAc:toluene). IR (film)/cm-1 3169 (OH), 2982 (CH), 1719 (C=O), 1177, 1028, 713. 1 Major diastereoisomer: H NMR (400 MHz, CDCl3) d 8.47 (br s, 1 H, He), 8.40-8.38

(m, 1 H, Hh), 7.79-7.73 (m, 1 H, Hf), 7.28-7.24 (m, 1 H, Hg), 4.73 (br s, 1 H, OH), 4.26

(d, J = 7.2 Hz, 1 H, CH(OH)), 4.13–4.00 (m, 2 H, CH2CH3), 1.85-1.76 (m, 1 H, Hc),

225

1.83-1.74 (m, 1 H, Hd), 1.23-1.18 (m, 1 H, Ha), 1.21 (t, J = 7.1 Hz, 3 H, CH3), 0.99 13 (ddd, J = 8.4, 6.4, 4.5 Hz, 1 H, Hb). C NMR (101 MHz, CDCl3) d 173.5 (C=O), 148.5 (Ar-C), 147.3 (Ar-C), 139.1 (Ar-C quat), 134.0 (Ar-C), 123.6 (Ar-C), 72.7 (CH(OH)),

60.6 (CH2CH3), 29.0 (C(Hd)), 18.7 (C(Hc)), 14.1 (CH3), 12.5 (C(Ha)(Hb)). 1 Minor diastereoisomer: H NMR (400 MHz, CDCl3) d 8.47 (br s, 1 H, He), 8.40-8.38

(m, 1 H, Hh), 7.79-7.73 (m, 1 H, Hf), 7.28-7.24 (m, 1 H, Hg), 4.73 (br s, 1 H, OH), 4.50

(d, J = 5.7 Hz, 1 H, CH(OH)), 4.13–4.00 (m, 2 H, CH2CH3), 1.81-1.71 (m, 1 H, Hd),

1.78-1.71 (m, 1 H, Hc), 1.23-1.18 (m, 1 H, Ha), 1.20 (t, J = 7.1 Hz, 3 H, CH3), 1.14 13 (ddd, J = 8.5, 6.5, 4.3 Hz, 1 H, Hb). C NMR (101 MHz, CDCl3) d 173.6 (C=O), 148.5 (Ar-C), 147.4 (Ar-C), 139.2 (Ar-C quat), 134.1 (Ar-C), 123.6 (Ar-C), 71.1 (CH(OH)),

60.6 (CH2CH3), 28.3 (C(Hd)), 17.7 (C(Hc)), 14.1 (CH3), 12.1 (C(Ha)(Hb)). + + HRMS (ES) m/z Calcd for C12H16NO3 [M+H] : 222.1130; Found: 222.1131.

(trans)-Ethyl 2-(3-hydroxyoxetan-3-yl)cyclopropane-1-carboxylate (111)

O O Hc H Ha d Hb OH O

i-PrMgCl (0.32 mL, 1.87 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (trans)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 96 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. 3-Oxetanone (52 µL, 0.8 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 1 h. The reaction was warmed to rt, sat. aq NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (10 mL) was added and the mixture was extracted with CH2Cl2 (3 × 10 mL then 7 × 20 mL) followed by EtOAc (6 ´ 20 mL). The combined organic phases were concentrated under reduced pressure, dissolved in CH2Cl2, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:39 MeOH:CH2Cl2) gave cyclopropane 111 (49 mg, -1 66%) as a pale yellow oil. Rf = 0.10 (1:39 MeOH:CH2Cl2). IR (film)/cm 3400 (OH), 2977 (CH), 2956 (CH), 2876 (CH), 1723 (C=O), 1702 (C=O), 1316, 1178. 1H NMR

(400 MHz, CDCl3) d 4.58 (d, J = 6.8 Hz, 1 H, oxetane C(H)H), 4.54 (d, J = 6.8 Hz, 1 H, oxetane C(H)H), 4.50 (d, J = 6.8 Hz, 1 H, oxetane C(H)H), 4.44 (d, J =

226

6.8 Hz, 1 H, oxetane C(H)H), 4.19-4.07 (m, 2 H, CH2CH3), 3.29 (br s, 1 H, OH), 1.94

(ddd, J = 9.2, 6.5, 4.4 Hz, 1 H, Hd), 1.72 (ddd, J = 8.6, 4.9, 4.4 Hz, 1 H, Hc), 1.26 (t,

J = 7.1 Hz, 3 H, CH3), 1.25–1.18 (m, 1 H, Ha), 1.10 (ddd, J = 8.6, 6.5, 4.6 Hz, 1 H, Hb). 13 C NMR (101 MHz, CDCl3) d 173.8 (C=O), 83.3 (oxetane-CH2), 82.5 (oxetane-CH2),

72.8 (oxetane-C quat), 60.8 (CH2CH3), 27.2 (C(Hd)), 16.4 (C(Hc)), 14.1 (CH3), 10.8 + + (C(Ha)(Hb)). HRMS (CI+) m/z Calcd for C9H18NO4 [M+NH4] : 204.1236; Found: 204.1226.

(trans)-Ethyl-2-[bis(4-chlorophenyl)(hydroxyl)methyl]cyclopropane-1- carboxylate (112)

O O Hc H Ha d OH Hb

Cl Cl

NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (20 mL) was added and the mixture was extracted with EtOAc (5 ´ 20 mL). The combined organic phases were washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (3:1 pentane:toluene) gave cyclopropane -1 112 (117 mg, 80%) as a pale yellow oil. Rf = 0.59 (5:1 pentane:Et2O). IR (film)/cm 2969 (CH), 2923 (CH), 2877 (CH), 1652 (C=O), 1587, 1490, 1399, 1089, 1013, 906, 1 728. H NMR (400 MHz, CDCl3) d 7.39–7.28 (m, 8 H, 8 ´ Ar-H), 4.13 (q, J = 7.2 Hz,

2 H, CH2CH3), 2.18 (ddd, J = 9.0, 6.7, 4.5 Hz, 1 H, Hc), 1.95 (br s, 1 H, OH), 1.79 (ddd,

J = 8.7, 4.8, 4.5 Hz, 1 H, Hd), 1.30–1.23 (m, 4 H, Hb + CH3), 1.13 (ddd, J = 8.7, 6.7, 13 4.3 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 173.8 (C=O), 144.7 (Ar-C-Cl), 144.4 (Ar-C-Cl), 133.5 (2 ´ Ar-C quat), 128.5 (2 ´ Ar-C), 128.4 (2 ´ Ar-C), 128.0 (2 ´ Ar-C),

227

127.9 (2 ´ Ar-C), 75.6 (C(OH)), 60.8 (CH2CH3), 31.5 (C(Hc)), 17.5 (C(Hd)), 14.2 (CH3), + + 11.9 (C(Ha)(Hb)). FTMS (+p NSI) m/z Calcd for C19H18O3Cl2Na [M+Na] : 387.0525; Found: 387.0526.

(trans)-Ethyl 2-[hydroxydi(pyridin-2-yl)methyl]cyclopropane-1-carboxylate (113)

O O Hc

Hd Ha OH Hb

N N

Purification by flash column chromatography (1:1 pentane:Et2O) gave cyclopropane -1 113 (107 mg, 90%) as a colourless oil. Rf = 0.23 (1:1 pentane:Et2O). IR (film)/cm 3319 (OH), 3057 (CH), 2982 (CH), 1718 (C=O), 1587, 1571, 1433, 1177, 749. 1H NMR

(400 MHz, CDCl3) d 8.52–8.49 (m, 2 H, 2 ´ Ar-H), 7.85–7.82 (m, 2 H, 2 ´ Ar-H), 7.69–7.64 (m, 2 H, 2 ´ Ar-H), 7.18–7.14 (m, 2 H, 2 ´ Ar-H), 6.28 (br s, 1 H, OH),

4.11–4.00 (m, 2 H, CH2CH3), 2.85 (ddd, J = 9.0, 6.5, 4.4 Hz, 1 H, Hc), 1.83–1.79 (m,

1 H, Hd), 1.22–1.16 (m, 4 H, Ha + CH3), 1.10 (ddd, J = 9.0, 4.8, 3.9 Hz, 1 H, Hb). 13 C NMR (101 MHz, CDCl3) d 174.2 (C=O), 163.0 (Ar-C quat), 162.9 (Ar-C quat), 147.53 (Ar-C), 147.47 (Ar-C), 136.8 (2 ´ Ar-C), 122.2 (2 ´ Ar-C), 120.9 (2 ´ Ar-C), 74.8

(C(OH)), 60.2 (CH2CH3), 31.3 (C(Hc)), 16.6 (C(Hd)), 14.2 (CH3), 11.2 (C(Ha)(Hb)). + + HRMS (EI) m/z Calcd for C17H18N2O3 [M] : 298.1317; Found: 298.1315.

228

(trans)-Ethyl 2-benzoylcyclopropane-1-carboxylate (114)

O O Hc H Ha d Hb O

0 °C for 3 h. The reaction was warmed to rt, sat. aq NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (10 mL) was added and the mixture was extracted with EtOAc (5 × 30 mL). The combined organic phases were washed with brine, dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash chromatography (9:1–2:1 n-hexane:EtOAc) gave cyclopropane 114 (44 mg, 38%) as -1 a colourless oil. Rf = 0.22 (9:1 n-hexane:EtOAc). IR (film)/cm 3063 (CH), 2982 (CH), 1 1724 (C=O), 1672, 1332, 1207, 1004. H NMR (400 MHz, CDCl3) d 8.04–8.02 (m, 2 H, 2 ´ Ph-H), 7.62–7.58 (m, 1 H, Ph-H), 7.50 (t, J = 7.6 Hz, 2 H, 2 ´ Ph-H), 4.19 (q, J =

7.1 Hz, 2 H, CH2CH3), 3.20 (ddd, J = 8.7, 5.8, 3.9 Hz, 1 H, Hc), 2.39 (ddd, J = 8.7, 5.9, 13 3.9 Hz, 1 H, Hd), 1.66–1.58 (m, 2 H, Ha + Hb), 1.30 (t, J = 7.1 Hz, 3 H, CH3). C NMR

(101 MHz, CDCl3) d 197.0 (C=O ketone), 172.3 (C=O ester), 137.0 (Ph-C quat), 133.3

(Ph-C), 128.6 (2 ´ Ph-C), 128.2 (2 ´ Ph-C), 61.1 (CH2CH3), 25.9 (C(Hc)), 24.7 (C(Hd)), + + 17.9 (C(Ha)(Hb)), 14.2 (CH3). FTMS (+p APCI) m/z Calcd for C13H15O3 [M+H] : 219.1016; Found: 219.1016. The observed data (1H) was consistent with that previously reported.335

229

(trans)-Ethyl 2-(phenylcarbamoyl)cyclopropane-1-carboxylate (115)

O O Hc H Ha d Hb NH O

i-PrMgCl (0.32 mL, 1.85 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (trans)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 96 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. Phenyl isocyanate (87 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 6 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (20 mL) was added and the mixture was extracted with

Et2O (5 × 30 mL). The combined organic phases were washed with brine, dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:1 pentane:Et2O) gave cyclopropane 115 (70 mg, 75%) as -1 a white solid. Rf = 0.31 (1:1 pentane:Et2O). mp = 90-91°C. IR (film)/cm 3282 (NH), 2977 (CH), 2934 (CH), 1722 (C=O), 1652, 1440, 1365, 1338, 1257, 1206, 1185, 1172, 1 988, 939, 750, 693. H NMR (400 MHz, CDCl3) d 7.97 (br s, 1 H, NH), 7.53–7.51 (m, 2 H, 2 ´ Ph-H), 7.33–7.30 (m, 2 H, 2 ´ Ph-H), 7.13–7.09 (t, J = 7.4 Hz, 1 H, Ph-H),

4.19 (q, J = 7.1 Hz, 2 H, CH2CH3), 2.28 (ddd, J = 9.1, 5.7, 3.9 Hz, 1 H, Hc), 2.12 (ddd,

J = 8.9, 5.8, 3.9 Hz, 1 H, Hd), 1.58 (ddd, J = 9.1, 5.8, 3.8 Hz, 1 H, Hb), 1.43 (ddd, J = 13 8.9, 5.7, 3.8 Hz, 1 H, Ha), 1.30 (t, J = 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 173.0 (C=O ester), 168.4 (C=O amide), 137.8 (Ph-C quat), 129.0 (2 ´ Ph-C), 124.3

(Ph-C), 119.7 (2 ´ Ph-C), 61.3 (CH2CH3), 25.1 (C(Hd)), 22.0 (C(Hc)), 15.3 (C(Ha)(Hb)), + + 14.2 (CH3). HRMS (ES) m/z Calcd for C13H16NO3 [M+H] : 234.1130; Found: 234.1137.

230

(trans)-Ethyl 2-[(4-methoxyphenyl)sulfanyl]cyclopropane-1-carboxylate (116)

O O Hc

Hd Ha H S OMe b

i-PrMgCl (0.32 mL, 1.85 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (trans)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 96 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. A solution of bis(4-methoxyphenyl)disulfide (223 mg, 0.80 mmol, 2.0 equiv) in THF (0.5 mL) was added and the reaction stirred at 0 °C for 6 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (20 mL) was added and the mixture was extracted with EtOAc (5 × 30 mL). The combined organic phases were washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (15:1 pentane:Et2O) gave cyclopropane 116 (55 mg, 55%) as a yellow oil. Rf = 0.24 (9:1 pentane:Et2O). IR (film)/cm-1 2981 (CH), 2961 (CH), 2836 (CH), 1721 (C=O), 1494, 1242, 1173, 1030, 1 821. H NMR (400 MHz, CDCl3) d 7.34–7.31 (m, 2 H, 2 ´ Ar-H), 6.89–6.85 (m, 2 H,

2 ´ Ar-H), 4.20–4.09 (m, 2 H, CH2CH3), 3.81 (s, 3 H, OCH3), 2.74 (ddd, J = 8.3, 5.7,

3.6 Hz, 1 H, Hc), 1.90 (ddd, J = 8.8, 5.3, 3.6 Hz, 1 H, Hd), 1.57 (ddd J = 8.3, 5.3, 5.0 Hz,

1 H, Hb), 1.27 (t, J = 7.2 Hz, 3 H, CH2CH3), 1.21 (ddd, J = 8.8, 5.7, 5.0 Hz, 1 H, Ha). 13 C NMR (101 MHz, CDCl3) d 172.3 (C=O), 158.8 (Ar-C-OCH3), 131.2 (2 ´ Ar-C),

126.5 (Ar-C quat), 114.7 (2 ´ Ar-C), 60.8 (CH2CH3), 55.3 (OCH3), 24.5 (C(Hd)), 24.2 + (C(Hc)), 17.2 (C(Ha)(Hb)), 14.2 (CH2CH3). FTMS (+p APCI) m/z Calcd for C13H17O3S [M+H]+: 253.0893; Found: 253.0891.

231

(trans)-Ethyl 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)cyclopropane-1- carboxylate (117)

O O Hc

Hd Ha Hb B O O

MeOH (1 mL) added and stirred for 5 min. Et2O (10 mL) was added and the mixture filtered, then concentrated under reduced pressure. Purification by flash column chromatography (4:1 pentane:Et2O) gave cyclopropane 117 (52 mg, 54%) as a colourless oil. IR (film)/cm-1 2980 (CH), 2932 (CH), 1727 (C=O), 1424, 1370, 1325, 1 1177, 1141, 855. H NMR (400 MHz, CDCl3) d 4.17–4.05 (m, 2 H, CH2CH3), 1.75 (ddd,

J = 7.7, 5.1, 4.9 Hz, 1 H, Hc), 1.26–1.19 (m, 16 H, Hd + 5 ´ CH3), 0.98 (ddd, J = 7.7, 13 7.3, 3.0 Hz, 1 H, Hb), 0.57 (ddd, J = 10.1, 7.3, 5.1 Hz, 1 H, Ha). C NMR (101 MHz,

CDCl3) d 174.2 (C=O), 83.4 (2 ´ C(CH3)2), 60.5 (CH2CH3), 29.7 (C(Hd)), 24.7 (2 ´ 11 CH3), 24.6 (2 ´ CH3), 18.5 (C(Hc)), 14.2 (CH2CH3), 13.0 (C(Ha)(Hb)). B NMR 11 + + (128 MHz, CDCl3) d 32.58 (B(pin)). HRMS (EI) m/z Calcd for C12H21 BO4 [M] : 240.1533; Found: 240.1528.

(trans)-Ethyl 2-(triethoxysilyl)cyclopropane-1-carboxylate (118)

O O Hc H Ha d Hb Si OEt EtO OEt

232

Chlorotriethoxysilane (157 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 6 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (20 mL) was added and the mixture was extracted with EtOAc (5 × 30 mL). The combined organic phases were washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (4:1 pentane:Et2O) gave cyclopropane 118 (55 mg, 43%) as a pale yellow oil. IR (film)/cm-1 2976 (CH), 2934 (CH), 1722 (C=O), 1389, 1 1264, 1166, 1100, 1073, 953, 776. H NMR (400 MHz, CDCl3) d 4.14 (q, J = 7.1 Hz, 2

H, (C=O)OCH2), 3.91–3.81 (m, 6 H, 3 ´ SiOCH2), 1.74 (ddd, J = 7.7, 5.9, 4.3 Hz, 1 H,

Hc), 1.28–1.18 (m, 13 H, Ha + 4 ´ CH3), 0.96 (ddd, J = 7.7, 7.7, 3.1 Hz, 1 H, Hb), 0.36 13 (ddd, J = 10.8, 7.7, 5.9 Hz, 1 H, Hd). C NMR (101 MHz, CDCl3) d 174.6 (C=O), 60.5

(CH2), 59.1 (CH2), 58.7 (2 ´ CH2), 18.2 (2 ´ CH3), 18.0 (CH3), 16.3 (C(Hc)), 14.2 (CH3), + + 11.2 (C(Ha)(Hb)), 2.9 (C(Hd)). HRMS (EI) m/z Calcd for C12H24O5Si [M] : 276.1393; Found: 276.1405.

(trans)-Ethyl 2-formylcyclopropane-1-carboxylate (119)

O O Hc H Ha d Hb O

i-PrMgCl (0.32 mL, 1.85 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (trans)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 96 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. N,N-Dimethylformamide (62 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 6 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture stirred for 5 min. H2O (20 mL) was added and the mixture was extracted with ether (5 × 30 mL). The combined organic phases were washed with brine, with the aqueous being extracted with Et2O (30 mL). The combined organic phases were dried (MgSO4), filtered and concentrated under reduced pressure.

Purification by flash column chromatography (5:1 pentane:Et2O) gave cyclopropane -1 119 (48 mg, 85%) as a colourless oil. Rf = 0.17 (5:1 pentane:Et2O). IR (film)/cm 2984 1 (CH), 2849 (CH), 2738 (CH), 1182, 980. H NMR (400 MHz, CDCl3) d 9.31 (d, J = 4.2

233

Hz, 1 H, C(O)H), 4.18 (q, J = 7.1 Hz, 2 H, CH2CH3), 2.44 (dddd, J = 8.5, 5.8, 4.2, 3.9

Hz, 1 H, Hd), 2.26 (ddd, J = 8.9, 6.0, 3.9 Hz, 1 H, Hc), 1.61 (ddd, J = 8.5, 6.0, 4.4 Hz, 13 1 H, Ha), 1.51 (ddd, J = 8.9, 5.8, 4.4 Hz, 1 H, Hb), 1.28 (t, J = 7.1 Hz, 3 H, CH3). C

NMR (101 MHz, CDCl3) d 198.1 (C=O aldehyde), 171.0 (C=O ester), 61.3 (CH2CH3), 1 13 30.6 (C(Hd)), 22.2 (C(Hc)), 14.8 (C(Ha)(Hb)), 14.1 (CH3). The observed data ( H, C) was consistent with that previously reported.336,337

(cis)-Ethyl-2-iodocyclopropanecarboxylate (107)

O Hc O H Ha d I Hb

i-PrMgCl (0.32 mL, 1.87 M in THF, 0.60 mmol, 1.5 equiv) was added to a −78 °C solution of (cis)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 97 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. A solution of I2 (203 mg, 0.80 mmol, 2.0 equiv) in THF (0.5 mL) was added and the reaction stirred at −78 °C for 1 h. The reaction was warmed to rt, sat. aq NH4Cl (5 mL) added and the mixture was stirred for 5 min. Water (10 mL) was added and the mixture was extracted with CH2Cl2 (3 × 30 mL). The combined organic phases were washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure.

Purification by flash column chromatography (100% n-hexane to 10:1 n-hexane:Et2O) gave cyclopropane 107 (56 mg, 58%) as a yellow oil. IR (film)/cm-1 2981 (CH), 1726 1 (C=O), 1396, 1380, 1248, 1175. H NMR (400 MHz, CDCl3) d 4.30–4.17 (m, 2 H,

CH2CH3), 2.82 (ddd, J = 8.3, 8.1, 6.5 Hz, 1 H, Hd), 1.87 (ddd, J = 8.3, 8.3, 6.5 Hz, 1 H,

Hc), 1.52 (ddd, J = 8.3, 8.1, 6.2 Hz, 1 H, Ha), 1.42 (ddd, J = 6.5, 6.5, 6.2 Hz, 1 H, Hb), 13 1.32 (t, J = 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 169.9 (C=O), 61.2 (CH2),

19.2 (C(Hc)), 16.3 (C(Ha)(Hb)), 14.4 (CH3), -14.6 (C(Hd)). HRMS (ES) m/z Calcd for + + 1 13 C6H10O2I [M+H] : 240.9726; Found: 240.9710. The observed data (IR, H, C) was consistent with that previously reported.338

234

(cis)-4-Cyclopentyl-3-oxabicyclo[3.1.0]hexan-2-one (120)

O H c O

Ha Hb Hd

Purification by flash column chromatography (2:1 pentane:Et2O) gave cyclopropane 120 as a mixture of two diastereoisomers (dr = 61:39, 57 mg, 86%) as a yellow oil. -1 Rf = 0.24 (2:1 pentane:Et2O). IR (film)/cm 2953 (CH), 2869 (CH), 1760 (C=O), 1452, 1330, 1183, 959. 1 Major diastereoisomer: H NMR (400 MHz, CDCl3) d 4.18 (d, J = 7.5 Hz, 1 H,

CH(CHd)), 2.12-2.03 (m, 1 H, CH(CH2)2), 2.06-2.03 (m, 2 H, Hc + Hd), 1.88-1.76 (m,

2 H, CH2), 1.69-1.53 (m, 4 H, 2 ´ CH2), 1.45-1.35 (m, 2 H, CH2), 1.28-1.19 (m, 1 H, 13 Ha), 0.84 (dd, J = 4.7, 4.0 Hz, 1 H, Hb). C NMR (101 MHz, CDCl3) d 176.2 (C=O),

84.7 (CH(CHd)), 45.0 (CH(CH2)2), 28.0 (CH2), 27.7 (CH2), 25.5 (CH2), 25.3 (CH2), 21.5

(C(Hd)), 17.8 (C(Hc)), 12.2 (C(Ha)(Hb)). 1 Minor diastereoisomer: H NMR (400 MHz, CDCl3) d 4.28 (dd, J = 9.6, 4.4 Hz, 1 H,

CH(CHd)), 2.21-2.16 (m, 1 H, Hc), 2.06-2.03 (m, 1 H, Hd), 1.97-1.88 (m, 1 H,

CH(CH2)2), 1.88-1.76 (m, 2 H, CH2), 1.69-1.53 (m, 4 H, 2 ´ CH2), 1.45-1.35 (m, 2 H, 13 CH2), 1.11-1.06 (m, 1 H, Ha), 0.96 (ddd, J = 4.7, 4.7, 3.2 Hz, 1 H, Hb). C NMR

(101 MHz, CDCl3) d 176.3 (C=O), 84.1 (CH(CHd)), 42.2 (CH(CH2)2), 30.5 (CH2), 28.1

(CH2), 25.4 (CH2), 25.1 (CH2), 20.8 (C(Hd)), 18.5 (C(Hc)), 8.8 (C(Ha)(Hb)). + + FTMS (APCI) m/z Calcd for C10H15O2 [M+H] : 167.1067; Found: 167.1068.

235

(cis)-4-Phenyl-3-oxabicyclo[3.1.0]hexan-2-one (121)

O H c O

Ha Hb Hd

0 °C for 1 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture was stirred for 5 min. H2O (10 mL) was added and the mixture was extracted with CH2Cl2 (3 × 30 mL). The combined organic phases were washed with brine, dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (10:1 n-hexane:Et2O) gave cyclopropane 121 as a mixture of two diastereoisomers (dr = 56:44, 48 mg, 69%) as a white solid. Rf = 0.59 (1:1 pentane:EtOAc). mp = 33-34 °C. IR (film)/cm-1 3034 (CH), 3008 (CH), 2930 (CH), 1762 (C=O), 1454, 1312, 1180, 969. 1 Major diastereoisomer: H NMR (400 MHz, CDCl3) d 7.44–7.32 (m, 5 H, 5 ´ Ph-H),

5.34 (s, 1 H, CH(CHd)), 2.31–2.24 (m, 1 H, Hd), 2.29–2.21 (m, 1 H, Hc), 1.37 (ddd, J = 13 8.9, 7.6, 4.9 Hz, 1 H, Ha), 1.10 (ddd, J = 4.9, 4.7, 3.5 Hz, 1 H, Hb). C NMR (101 MHz,

CDCl3) d 175.9 (C=O), 139.7 (Ph-C quat), 128.9 (2 ´ Ph-C), 128.8 (Ph-C), 125.5 (2 ´

Ph-C), 81.6 (CH(CHd)), 24.7 (C(Hd)), 17.8 (C(Hc)), 12.9 (C(Ha)(Hb)). 1 Minor diastereoisomer: H NMR (400 MHz, CDCl3) d 7.44–7.32 (m, 5 H, 5 ´ Ph-H),

5.75 (d, J = 4.9 Hz, 1 H, CH(CHd)), 2.57 (dddd, J = 7.5, 4.9, 4.9, 4.9 Hz, 1 H, Hd),

2.31–2.21 (m, 1 H, Hc), 1.14 (ddd, J = 9.0, 7.5, 5.1 Hz, 1 H, Ha), 0.89 (ddd, J = 5.1, 13 4.9, 3.3 Hz, 1 H, Hb). C NMR (101 MHz, CDCl3) d 175.6 (C=O), 137.4 (Ph-C quat),

128.5 (2 ´ Ph-C), 128.1 (Ph-C), 125.4 (2 ´ Ph-C), 79.2 (CH(CHd)), 22.2 (C(Hd)), 19.1

(C(Hc)), 9.7 (C(Ha)(Hb)). + + HRMS (EI) m/z Calcd for C11H10O2 [M] : 174.0681; Found: 174.0674. The observed data (IR, 1H, 13C) was consistent with that previously reported.284

236

(cis)-Ethyl 2-[hydroxy(pyridine-3-yl)methyl]cyclopropane-1-carboxylate (122)

O Hc O Hf Hg H Ha d Hb Hh HO N He

i-PrMgCl (0.32 mL, 1.87 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (cis)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 97 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. 3-Pyridinecarboxaldehyde (75 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 1 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (10 mL) was added and the mixture was extracted with CH2Cl2 (6 × 20 mL) then EtOAc (6 ´ 20 mL). The combined organic phases were concentrated under reduced pressure, dissolved in CH2Cl2, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (3:1 EtOAc:toluene) gave cyclopropane 122 as a mixture of two diastereoisomers (dr = 57:43, 76 mg, 86%) as a colourless oil. Rf = 0.23 (3:1 EtOAc:toluene). IR (film)/cm-1 3184 (OH), 2981 (CH), 2929 (CH), 2848 (CH), 1774 (C=O), 1183. 1 Major diastereoisomer: H NMR (400 MHz, CDCl3) d 8.62–8.45 (m, 2 H, 2 ´ Ar-H), 7.80–7.63 (m, 1 H, Ar-H), 7.34–7.24 (m, 1 H, Ar-H), 5.72 (d, J = 4.8 Hz, 1 H, CH(OH)),

4.16–4.07 (m, 2 H, CH2CH3), 1.90 (ddd, J = 8.3, 8.3, 5.8 Hz, 1 H, Hc), 1.70–1.62 (m, 13 1 H, Hd), 1.26–1.09 (m, 4 H, Ha + CH3), 0.80–0.79 (m, 1 H, Hb). C NMR (101 MHz,

CDCl3) d 173.2 (C=O), 149.4 (Ar-C), 147.5 (Ar-C), 139.8 (Ar-C quat), 133.6 (Ar-C),

123.4 (Ar-C), 77.1 (CH(OH)), 60.8 (CH2CH3), 28.8 (C(Hd)), 19.0 (C(Hc)), 12.5 (CH3),

9.7 (C(Ha)(Hb)). 1 Minor diastereoisomer: H NMR (400 MHz, CDCl3) d 8.62–8.45 (m, 2 H, 2 ´ Ar-H), 7.80–7.63 (m, 1 H, Ar-H), 7.34–7.24 (m, 1 H, Ar-H), 4.81 (d, J = 9.2 Hz, 1 H, CH(OH)),

4.16–4.07 (m, 2 H, CH2CH3), 2.62–2.57 (m, 1 H, Hd), 2.25 (ddd, J = 6.4, 4.1, 3.6 Hz,

1 H, Hc), 1.46–1.36 (m, 1 H, Ha), 1.24 (t, J = 6.8 Hz, 3 H, CH3), 1.17–1.09 (m, 1 H, Hb). 13 C NMR (101 MHz, CDCl3) d 174.9 (C=O), 148.5 (Ar-C), 146.9 (Ar-C), 135.1 (Ar-C

237

quat), 133.4 (Ar-C), 123.7 (Ar-C), 79.1 (CH(OH)), 69.6 (CH2CH3), 21.6 (C(Hd)), 18.5

(C(Hc)), 14.1 (CH3), 12.8 (C(Ha)(Hb)). + + HRMS (APCI) m/z Calcd for C12H16NO3 [M+H] : 222.1125; Found: 222.1124.

(cis)-4,4-Diethyl-3-oxabicyclo[3.1.0]hexan-2-one (123)

O H c O

Ha Hb Hd

i-PrMgCl (0.32 mL, 1.82 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (cis)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 97 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. Pentan-3-one (85 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 3 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (20 mL) was added and the mixture was extracted with EtOAc

(5 ´ 20 mL). The combined organic phases were washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (2:1 pentane:Et2O) gave cyclopropane 123 (30 mg, 49%) as a pale -1 yellow oil. Rf = 0.23 (2:1 pentane:Et2O). IR (film)/cm 2973 (CH), 2942 (CH), 2885 1 (CH), 1766 (C=O), 1463, 1233, 1000, 941. H NMR (400 MHz, CDCl3) d 2.12 (ddd, J =

8.9, 5.7, 3.1 Hz, 1 H, Hc), 1.99–1.95 (m, 1 H, Hd), 1.87–1.71 (m, 3 H, 3 ´ C(H)H),

1.61–1.52 (m, 1 H, C(H)H), 1.11 (ddd, J = 8.9, 7.6, 5.1 Hz, 1 H, Ha), 1.01–0.94 (m, 13 7 H, Hb + 2 ´ CH3). C NMR (101 MHz, CDCl3) d 176.0 (C=O), 87.7 (C(CH2CH3)2),

30.9 (CH2CH3), 28.1 (CH2CH3), 24.7 (C(Hd)), 19.1 (C(Hc)), 9.7 (C(Ha)(Hb)), 8.4 (CH3), + + 7.1 (CH3). HRMS (CI+) m/z Calcd for C9H15O2 [M+H] : 155.1072; Found: 155.1071.

238

(cis)-4,4-Bis(4-chlorophenyl)-3-oxabicyclo[3.1.0]hexan-2-one (124)

O H c O Cl Ha Hb Hd

Purification by flash column chromatography (2:1 pentane:Et2O–100% Et2O) gave cyclopropane 124 (83 mg, 65%) as a white solid. mp = 153–155 °C. Rf = 0.17 (1:2 -1 pentane:Et2O). IR (film)/cm 2968 (CH), 2932 (CH), 1644 (C=O), 1583, 1443, 1365, 1 1087, 1020, 748, 691. H NMR (400 MHz, CDCl3) d 7.42–7.26 (m, 8 H, 8 ´ Ar-H), 2.75

(ddd, J = 7.5, 5.5, 4.6 Hz, 1 H, Hc), 2.35 (ddd, J = 9.0, 5.5, 3.4 Hz, 1 H, Hd), 1.43 (ddd, 13 J = 9.0, 7.5, 5.3 Hz, 1 H, Ha), 0.94 (ddd, J = 5.3, 4.6, 3.4 Hz, 1 H, Hb). C NMR

(101 MHz, CDCl3) d 174.5 (C=O), 142.4 (Ar-C quat), 139.4 (Ar-C quat), 134.3 (Ar-C quat), 134.2 (Ar-C quat), 128.9 (2 ´ Ar-C), 128.8 (2 ´ Ar-C), 128.0 (2 ´ Ar-C), 126.7

(2 ´ Ar-C), 87.6 (C(Ar)2), 27.9 (C(Hc)), 19.8 (C(Hd)), 13.1 (C(Ha)(Hb)). HRMS (ASAP+) + + m/z Calcd for C17H13O2Cl2 [M+H] : 319.0293; Found: 319.0290.

239

(cis)-Ethyl 2-[hydroxydi(pyridin-2-yl)methyl]cyclopropane-1-carboxylate (125) and (cis)-4,4-Di(pyridin-2-yl)-3-oxabicyclo[3.1.0]hexan-2-one (126)

O O Hc O H c O N Hd Ha Ha H OH b Hb Hd N N N

125 126

NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (10 mL) was added and the mixture was extracted with EtOAc (3 × 30 mL). The combined organic phases were washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (EtOAc) gave alcohol 125 (51 mg, 43%) as a white oil followed by lactone 126 (15 mg, 15%) as a yellow gum. (cis)-Ethyl 2-[hydroxydi(pyridin-2-yl)methyl]cyclopropane-1-carboxylate (125) -1 Rf = 0.54 (EtOAc). IR (film)/cm 3339 (OH), 3058 (CH), 2982 (CH), 2935 (CH), 1728 1 (C=O), 1587, 1432, 1187, 1083, 994, 769, 749. H NMR (400 MHz, CDCl3) d 8.54 (m, 2 H, 2 ´ Ar-H), 7.89 (m, 1 H, Ar-H), 7.75 (m, 1 H, Ar-H), 7.65 (m, 2 H, 2 ´ Ar-H),

7.14–7.10 (m, 2 H, 2 ´ Ar-H), 6.08 (br s, 1 H, OH), 3.96–3.82 (m, 2 H, CH2CH3), 3.00

(ddd, J = 9.0, 8.7, 7.5 Hz, 1 H, Hc), 1.91 (ddd, J = 9.0, 8.7, 6.2 Hz, 1 H, Hd), 1.69 (ddd,

J = 7.5, 6.2, 4.9 Hz, 1 H, Hb), 1.15 (ddd, J = 8.7, 8.7, 4.9 Hz, 1 H, Ha), 1.02 (t, J = 13 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 174.8 (C=O), 164.6 (Ar-C quat), 164.0 (Ar-C quat), 148.2 (Ar-C), 147.9 (Ar-C), 136.7 (Ar-C), 136.2 (Ar-C), 121.9 (Ar-C), 121.8

(Ar-C), 121.1 (Ar-C), 120.3 (Ar-C), 77.2 (C(OH)) 60.7 (CH2CH3), 30.9 (C(Hc)), 19.6 + + (C(Hd)), 13.9 (CH3), 9.9 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C17H19N2O3 [M+H] : 299.1396; Found: 299.1397.

240

(cis)-4,4-Di(pyridin-2-yl)-3-oxabicyclo[3.1.0]hexan-2-one (126) -1 Rf = 0.22 (EtOAc). IR (film)/cm 3059 (CH), 3005 (CH), 2926 (CH), 2854 (CH), 1773 (C=O), 1587, 1572, 1465, 1433, 1201, 1028, 948, 749, 675. 1H NMR (400 MHz,

CDCl3) d 8.67–8.65 (m, 2 H, 2 ´ Ar-H), 7.73–7.64 (m, 2 H, 2 ´ Ar-H), 7.58 (d, J = 7.9 Hz, 1 H, Ar-H), 7.45 (d, J = 7.9 Hz, 1 H, Ar-H), 7.24–7.20 (m, 2 H, 2 ´ Ar-H), 3.57

(ddd, J = 7.7, 5.5, 4.7 Hz, 1 H, Hc), 2.27 (ddd, J = 8.8, 5.5, 3.3 Hz, 1 H, Hd), 1.36 (ddd, 13 J = 8.8, 7.7, 5.1 Hz, 1 H, Ha), 0.82 (ddd, J = 5.1, 4.7, 3.3 Hz, 1 H, Hb). C NMR

(101 MHz, CDCl3) d 175.2 (C=O), 160.1 (Ar-C quat), 159.3 (Ar-C quat), 149.6 (Ar-C), 149.2 (Ar-C), 136.9 (Ar-C), 136.7 (Ar-C), 123.1 (Ar-C), 122.8 (Ar-C), 120.9 (Ar-C),

120.7 (Ar-C), 88.8 (C(Ar)2), 26.3 (C(Hc)), 19.3 (C(Hd)), 12.3 (C(Ha)(Hb)). HRMS (ES) + + m/z Calcd for C15H13N2O2 [M+H] : 253.0977; Found: 253.0986.

(cis)-Ethyl 2-benzoylcyclopropane-1-carboxylate (127)

O Hc O H Ha d Hb O

0 °C for 3 h. The reaction was warmed to rt, sat. aq. NH4Cl (5 mL) added and the mixture stirred for 5 min. Water (10 mL) was added and the mixture was extracted with EtOAc (5 × 30 mL). The combined organic phases were washed with brine, dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (9:1 n-hexane:EtOAc) gave cyclopropane 127 (73 mg, 64%) -1 as a golden oil. Rf = 0.07 (9:1 n-hexane:EtOAc). IR (film)/cm 3063 (CH), 2983 CH), 1 1727 (C=O), 1681, 1382, 1226, 1185. H NMR (400 MHz, CDCl3) d 8.05–8.02 (m, 2 H, 2 ´ Ph-H), 7.58–7.54 (m, 1 H, Ph-H), 7.48–7.44 (m, 2 H, 2 ´ Ph-H), 3.99 (q, J = 7.1 Hz,

2 H, CH2CH3), 2.79 (ddd, J = 9.2, 8.3, 6.9 Hz, 1 H, Hc), 2.31 (ddd, J = 9.2, 8.3, 6.4 Hz,

241

1 H, Hd), 1.92 (ddd, J = 6.9, 6.4, 4.8 Hz, 1 H, Hb), 1.37 (ddd, J = 8.3, 8.3, 4.8 Hz, 1 H, 13 Ha), 1.05 (t, J = 7.1 Hz, 3 H, CH3). C NMR (101 MHz, CDCl3) d 194.5 (C=O ketone), 169.9 (C=O ester), 137.1 (Ph-C quat), 133.1 (Ph-C), 128.5 (2 ´ Ph-C), 128.3 (2 ´

Ph-C), 60.8 (CH2CH3), 26.2 (C(Hc)), 23.0 (C(Hd)), 13.9 (CH3), 11.5 (C(Ha)(Hb)). FTMS + + (+p APCI) m/z Calcd for C13H15O3 [M+H] : 219.1016; Found: 219.1014.The observed data (IR, 1H, 13C) was consistent with that previously reported.284,335

(cis)-Ethyl 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)cyclopropane-1- carboxylate (128)

O Hc O

Hd Ha Hb B O O

i-PrMgCl (0.32 mL, 1.85 M in THF, 0.60 mmol, 1.5 equiv) was added to a -78 °C solution of (cis)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 97 (95 mg, 0.40 mmol, 1.0 equiv) in THF (4.0 mL) over 10 s and the solution stirred for 10 min. 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (163 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 0 °C for 6 h. The reaction was warmed to rt, MeOH (1 mL) added and stirred for 5 min. The mixture was concentrated under reduced pressure, dissolved in acetonitrile (10 mL) and extracted with pentane (5 ´ 10 mL). The combined pentane phases were washed with acetonitrile (10 mL), then concentrated under reduced pressure to give cyclopropane 128 (79 mg, 82%) as a colourless oil. IR (film)/cm-1 2978 (CH), 2927 (CH), 2852 (CH), 1724 (C=O), 1380, 1 1319, 1142, 854. H NMR (400 MHz, CDCl3) d 4.24–4.05 (m, 2 H, CH2CH3), 1.83 (ddd,

J = 9.5, 7.8, 4.8 Hz, 1 H, Hc), 1.35–1.23 (m, 15 H, 5 ´ CH3) 1.12 (ddd, J = 8.7, 4.8,

3.6 Hz, 1 H, Hb), 1.06 (ddd, J = 9.2, 7.8, 3.6 Hz, 1 H, Ha), 0.42 (ddd, J = 9.5, 9.2, 13 8.7 Hz, 1 H, Hd). C NMR (101 MHz, CDCl3) d 174.4 (C=O), 83.5 (2 ´ C(CH3)2), 60.5

(CH2CH3), 29.7 (C(Hd)), 24.89 (2 ´ CH3), 24.87 (2 ´ CH3), 17.8 (C(Hc)), 14.3 (CH2CH3), 11 11.2 (C(Ha)(Hb)). B NMR (128 MHz, CDCl3) d 32.06 (B(pin)). HRMS (EI) m/z Calcd 11 + + for C11H18 BO4 [M-CH3] : 225.1298; Found: 225.1302.

242

Synthesis of 129–136 through sulfoxide–magnesium exchange, Negishi cross-coupling

(trans)-Ethyl 2-phenylcyclopropane-1-carboxylate (129)

O O Hc

Hd Ha Hb

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. Bromobenzene (84 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by purification by flash column chromatography (30:1 n-hexane:EtOAc) gave cyclopropane 129 -1 (56 mg, 74%) as a colourless oil. Rf = 0.21 (19:1 n-hexane:EtOAc). IR (film)/cm 3086 (CH), 3063 (CH), 3032 (CH), 2981 (CH), 2938 (CH), 2907 (CH), 1721 (C=O), 1178, 1 755, 698. H NMR (400 MHz, CDCl3) d 7.31–7.28 (m, 2 H, 2 ´ Ph-H), 7.22 (m, 1 H,

Ph-H), 7.13–7.11 (m, 2 H, 2 ´ Ph-H), 4.19 (q, J = 7.1 Hz, 2 H, CH2CH3), 2.54 (ddd, J =

9.4, 6.5, 4.2 Hz, 1 H, Hc), 1.92 (ddd, J = 8.5, 5.2, 4.2 Hz, 1 H, Hd), 1.62 (ddd, J = 9.4,

5.2, 4.6 Hz, 1 H, Hb), 1.33 (ddd, J = 8.5, 6.5, 4.6 Hz, 1 H, Ha), 1.30 (t, J = 7.1 Hz, 3 H, 13 CH3). C NMR (101 MHz, CDCl3) d 173.4 (C=O), 140.1 (Ph-C quat), 128.4 (2 ´ Ph-

C), 126.4 (Ph-C), 126.1 (2 ´ Ph-C), 60.7 (CH2CH3), 26.2 (C(Hc)), 24.2 (C(Hd)), 17.1 + + (C(Ha)(Hb)), 14.3 (CH3). HRMS (ES) m/z Calcd for C12H15O2 [M+H] : 191.1072; Found: 191.1071. The observed data (1H, 13C) was consistent with that previously reported.339

243

(cis)-Ethyl 2-phenylcyclopropane-1-carboxylate (130)

O Hc O H Ha d Hb

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. Bromobenzene (84 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by purification by flash column chromatography (9:1 pentane:Et2O) gave cyclopropane 130 (58 mg, -1 76%) as a yellow oil. Rf = 0.27 (9:1 pentane:Et2O). IR (film)/cm 3028 (CH), 2982 1 (CH), 2934 (CH), 1726 (C=O), 1382, 1179, 1157. H NMR (400 MHz, CDCl3) d

7.29–7.18 (m, 5 H, 5 ´ Ph-H), 3.88 (q, J = 7.1 Hz, 2 H, CH2CH3), 2.59 (ddd, J = 9.3,

8.8, 7.5 Hz, 1 H, Hc), 2.09 (ddd, J = 9.3, 7.8, 5.5 Hz, 1 H, Hd), 1.73 (ddd, J = 7.5, 5.5,

5.2 Hz, 1 H, Hb), 1.34 (ddd, J = 8.8, 7.8, 5.2 Hz, 1 H, Ha), 0.98 (t, J = 7.1 Hz, 3 H, CH3). 13 C NMR (101 MHz, CDCl3) d 171.0 (C=O), 136.6 (Ph-C quat), 129.3 (2 ´ Ph-C), 127.9

(2 ´ Ph-C), 126.6 (Ph-C), 60.2 (CH2CH3), 25.5 (C(Hc)), 21.8 (C(Hd)), 14.0 (CH3), 11.1 + + (C(Ha)(Hb)). HRMS (EI) m/z Calcd for C12H14O2 [M] : 190.0994; Found: 190.0988. The observed data (1H, 13C) was consistent with that previously reported.340

244

(trans)-Ethyl 2-(4-chlorophenyl)cyclopropane-1-carboxylate (131)

O O Hc

Hd Ha Hb

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. 1-Bromo, 4-chlorobenzene (153 mg, 0.80 mmol, 2.0 equiv) in THF (0.5 mL) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by purification by flash chromatography (9:1 pentane:Et2O) gave cyclopropane 131 (76 mg, 85%) as a pale yellow oil. Rf = 0.31 (9:1 pentane:Et2O). IR (film)/cm-1 2983 (CH), 2938 (CH), 1724 (C=O), 1497, 1328, 1186. 1H NMR (400 MHz,

CDCl3) d 7.27–7.23 (m, 2 H, 2 ´ Ar-H), 7.05–7.02 (m, 2 H, 2 ´ Ar-H), 4.18 (q, J =

7.1 Hz, 2 H, CH2CH3), 2.50 (ddd, J = 9.3, 6.4, 4.2 Hz, 1 H, Hc), 1.87 (ddd, J = 8.5, 5.4,

4.2 Hz, 1 H, Hd), 1.64–1.58 (m, 1 H, Hb), 1.29 (t, J = 7.1 Hz, 3 H, CH3), 1.28 (ddd, J = 13 8.5, 6.4, 4.6 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 173.1 (C=O), 138.6 (Ar-C-Cl),

132.2 (Ar-C quat), 128.5 (2 ´ Ph-C), 127.6 (2 ´ Ph-C), 60.8 (CH2CH3), 25.5 (C(Hc)), + + 24.2 (C(Hd)), 17.0 (C(Ha)(Hb)), 14.2 (CH3). HRMS (EI) m/z Calcd for C12H13O2Cl [M] : 224.0604; Found: 224.0608. The observed data (IR, 1H, 13C) was consistent with that previously reported.110,341

245

(trans)-Ethyl 2-(4-methoxyphenyl)cyclopropane-1-carboxylate (132)

O O Hc H Ha d Hb

OMe

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. 4-Bromoanisole (100 µL, 0.80 mmol, 2.0 equiv) in THF (0.5 mL) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by purification by flash column chromatography (15:1 pentane:Et2O) gave cyclopropane 132 (77 mg, 73%) as a cream crystalline solid. Rf = 0.24 (9:1 -1 pentane:Et2O). IR (film)/cm 2988 (CH), 2953 (CH), 2911 (CH), 2837 (CH), 1719 1 (C=O), 1516, 1252, 1186. H NMR (400 MHz, CDCl3) d 7.06–7.03 (m, 2 H, 2 ´ Ar-H),

6.85–6.81 (m, 2 H, 2 ´ Ar-H), 4.18 (q, J = 7.1 Hz, 2 H, CH2CH3), 3.79 (s, 3 H, OCH3),

2.49 (ddd, J = 9.3, 6.5, 4.2 Hz, 1 H, Hc), 1.83 (ddd, J = 8.4, 5.2, 4.2 Hz, 1 H, Hd), 1.58– 13 1.54 (m, 1 H, Hb), 1.29 (t, J = 7.1 Hz, 3 H, CH3), 1.27–1.24 (m, 1 H, Ha). C NMR

(101 MHz, CDCl3) d 173.5 (C=O), 158.3 (Ph-C-OMe), 132.0 (Ph-C quat), 127.3 (2 ´

Ar-H), 113.9 (2 ´ Ar-H), 60.6 (CH2CH3), 55.3 (OCH3), 25.6 (C(Hc)), 23.8 (C(Hd)), 16.7 + + (C(Ha)(Hb)), 14.3 (CH3). FTMS (+p APCI) m/z Calcd for C13H17O3 [M+H] : 221.1172; Found: 221.1182. The observed data (IR, 1H, 13C) was consistent with that previously reported.110,342

246

(trans)-Ethyl 2-[(E)-2-phenylethenyl]cyclopropane-1-carboxylate (133)

O O Hc

Hd Ha Hf Hb He

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. b-Bromostyrene (103 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by purification by flash column chromatography (19:1 pentane:Et2O) gave cyclopropane 133 (73 mg, -1 84%) as a golden oil. Rf = 0.46 (9:1 pentane:Et2O). IR (film)/cm 3027 (CH), 3000 (CH), 2983 (CH), 2911 (CH), 1718 (C=O), 1650 (C=C), 1341, 1175, 1036, 964, 754. 1 H NMR (400 MHz, CDCl3) d 7.33–7.28 (m, 4 H, 4 ´ Ph-H), 7.25–7.20 (m, 1 H, Ph-H),

6.55 (d, J = 15.8 Hz, 1 H, Hf), 5.77 (dd, J = 15.8, 8.7 Hz, 1 H, He), 4.17 (q, J = 7.1 Hz,

2 H, CH2CH3), 2.19 (dddd, J = 8.9, 8.7, 6.2, 3.9 Hz, 1 H, Hc), 1.77 (ddd, J = 8.4, 5.2,

3.9 Hz, 1 H, Hd), 1.49 (ddd, J = 8.9, 5.2, 4.4 Hz, 1 H, Hb), 1.29 (t, J = 7.1 Hz, 3 H, CH3), 13 1.11 (ddd, J = 8.4, 6.2, 4.4 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 173.3 (C=O), 137.0 (Ph-C quat), 130.3 (alkene CH), 130.1 (alkene CH), 128.5 (2 ´ Ph-C), 127.2

(Ph-C), 125.8 (2 ´ Ph-C), 60.7 (CH2CH3), 25.5 (C(Hc)), 22.3 (C(Hd)), 16.0 (C(Ha)(Hb)), 1 343 14.3 (CH3). The observed data ( H) was consistent with that previously reported.

247

(trans)-Ethyl 2-(pyridin-2-yl)cyclopropane-1-carboxylate (134)

O O Hc H Ha d Hb N

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. 2-Bromopyridine (76 µL, 0.80 mmol, 2.0 equiv) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by flash column chromatography (4:1 pentane:Et2O) gave cyclopropane 134 (46 mg, 60%) as a yellow -1 oil. Rf = 0.17 (4:1 pentane:Et2O). IR (film)/cm 2981 (CH), 2930 (CH), 1723 (C=O), 1 1595, 1476, 1330, 1179, 1049, 775. H NMR (400 MHz, CDCl3) d 8.46-8.44 (ddd, J = 4.9, 1.8, 1.0 Hz, 1 H, Ar-H), 7.59-7.56 (ddd, J = 7.6, 7.6, 1.8 Hz, 1 H, Ar-H), 7.25-7.22 (ddd, J = 7.6, 1.0, 1.0 Hz, 1 H, Ar-H), 7.11-7.07 (ddd, J = 7.6, 4.9, 1.0 Hz, 1 H, Ar-H),

4.17 (q, J = 7.2 Hz, 2 H, CH2CH3), 2.59 (ddd, J = 9.0, 6.1, 3.9 Hz, 1 H, Hc), 2.25 (ddd,

J = 8.3, 5.6, 3.9 Hz, 1 H, Hd), 1.65-1.57 (m, 2 H, Ha + Hb), 1.28 (t, J = 7.2 Hz, 3 H, 13 CH3). C NMR (101 MHz, CDCl3) d 173.4 (C=O), 158.9 (Ar-C quat), 149.4 (Ar-C),

136.0 (Ar-C), 122.5 (Ar-C), 121.3 (Ar-C), 60.7 (CH2CH3), 27.2 (C(Hc)), 24.3 (C(Hd)), + + 17.3 (C(Ha)(Hb)), 14.2 (CH3). HRMS (EI) m/z Calcd for C11H13NO2 [M] : 191.0946; Found: 191.0941. The observed data (1H, 13C) was consistent with that previously reported.341

248

(trans)-Ethyl 2-(pyrimidin-2-yl)cyclopropane-1-carboxylate (135)

O O Hc

Hd Ha Hb N N

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. 2-Bromopyrimidine (127 mg, 0.80 mmol, 2.0 equiv) in toluene (2.0 mL) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by flash column chromatography (4:1 pentane:Et2O) gave cyclopropane 135 -1 (45 mg, 59%) as a yellow oil. Rf = 0.28 (1:2 pentane:Et2O). IR (film)/cm 2982 (CH), 1 2938 (CH), 1725 (C=O), 1561, 1425, 1331, 1180. H NMR (400 MHz, CDCl3) d 8.60 (d, J = 4.9 Hz, 2 H, 2 ´ ArNCH), 7.11 (t, J = 4.9 Hz, 1 H, ArNCHCH), 4.17 (q, J =

7.1 Hz, 2 H, CH2CH3), 2.82 (ddd, J = 8.7, 6.2, 3.9 Hz, 1 H, Hc), 2.31 (ddd, J = 8.5, 5.7, 13 3.9 Hz, 1 H, Hd), 1.71-1.64 (m, 2 H, Ha + Hb), 1.28 (t, J = 7.1 Hz, 3 H, CH3). C NMR

(101 MHz, CDCl3) d 172.5 (C=O), 168.8 (Ar-C quat), 156.9 (2 ´ Ar-C), 118.6 (Ar-C),

60.8 (CH2CH3), 28.0 (C(Hc)), 25.0 (C(Hd)), 17.7 (C(Ha)(Hb)), 14.2 (CH3). HRMS (EI) + + m/z Calcd for C10H12N2O2 [M] : 192.0899; Found: 192.0908.

249

(trans)-tert-Butyl 3-[2-(ethoxycarbonyl)cyclopropyl]-1H-indole-1-carboxylate (136)

O O Hc H Ha d Hb N

O O

5.5 mol%) and ZnCl2 (82 mg, 0.60 mmol, 1.5 equiv) in THF (1.5 mL) was added and the solution stirred at 0 °C for 1 h. A solution of 3-Bromoindole-1-carboxylic acid tert-butyl ester (237 mg, 0.80 mmol, 2.0 equiv) in toluene (1.0 mL) was added and the reaction stirred at 25 °C for 15 h. MeOH (1 mL) was added and the mixture stirred for

15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by purification by flash column chromatography (19:1 pentane:Et2O) gave cyclopropane 136 (119 mg, 94%) as a -1 yellow gum. Rf = 0.15 (19:1 pentane:Et2O). IR (film)/cm 2980 (CH), 2934 (CH), 1722 1 (C=O), 1451, 1369, 1345, 1254, 1152, 1079, 743. H NMR (400 MHz, CDCl3) d 8.12 (d, J = 6.6 Hz, 1 H, ArNCH), 7.62 (d, J = 7.6 Hz, 1 H, Ar-H), 7.36–7.25 (m, 3 H, 3 ´

Ar-H), 4.23 (q, J = 7.1 Hz, 2 H, CH2CH3), 2.55 (dddd, J = 9.1, 6.6, 4.4, 1.1 Hz, 1 H,

Hc), 1.92 (ddd, J = 8.4, 5.1, 4.4 Hz, 1 H, Hd), 1.68 (s, 9 H, C(CH3)3), 1.61 (ddd, J = 9.1, 13 5.1, 4.3 Hz, 1 H, Hb), 1.34–1.29 (m, 4 H, Ha + CH2CH3). C NMR (101 MHz, CDCl3) d 173.6 (C=O ester), 149.6 (C=O carbamate), 135.4 (Ar-C quat), 130.4 (Ar-C quat), 124.6 (Ar-C), 122.6 (Ar-C), 122.0 (Ar-C), 120.3 (Ar-C quat), 119.0 (Ar-C), 115.3 (Ar-C),

83.7 (C(CH3)3), 60.7 (CH2CH3), 28.2 (C(CH3)3), 21.7 (C(Hd)), 17.1 (C(Hc)), 15.3 + + (C(Ha)(Hb)), 14.3 (CH2CH3). HRMS (EI) m/z Calcd for C19H23NO4 [M] : 329.1627; Found: 329.1635. The observed data (1H, 13C) was consistent with that previously reported.341

250

Synthesis of 137–144 through sequential scaffold functionalisation

(trans)-[2-(Benzenesulfonyl)cyclopropyl](4-methylpiperazin-1-yl)methanone (137)

O N N Hc H Ha d H S b O O

mCPBA (24 mg, 0.14 mmol, 3.0 equiv) was added to a solution of amide 86

(12.6 mg, 0.046 mmol, 1.0 equiv) in CH2Cl2 (2.3 mL) and the solution stirred for 6 h at

25 °C. Solid Na2S2O5 (26 mg, 3.0 equiv) was added and the mixture stirred for 30 min before being concentrated under reduced pressure. The mixture was redissolved in acetone containing 5% Et3N, then filtered. The filtrate was concentrated under reduced pressure then purified by flash column chromatography (2:8 MeOH:CH2Cl2 + 2% Et3N to 3:7 MeOH:CH2Cl2 + 2% Et3N). The material was dissolved in CH2Cl2 and filtered to give sulfone 137 (14 mg, quant) as a cream gum. Rf = 0.13 (3:7 MeOH:CH2Cl2). IR (film)/cm-1 2958 (CH), 1640 (C=O), 1447, 1306 (S=O), 1150, 1088, 979, 745, 726, 1 692. H NMR (400 MHz, CDCl3, 58:42 rotameric mixture, asterix denotes a rotameric signal) d 7.92–9.90 (m, 2 H, 2 ´ Ph-H), 7.71–7.67 (m, 1 H, Ph-H), 7.61–7.58 (m, 2 H, 2 ´ Ph-H), 4.44 (t, J = 15.1 Hz, 1 H, NC(H)H), 4.22–4.01 (m, 2 H, 2 ´ NC(H)H), 3.66–3.63 (m, 1 H, NC(H)H), 3.47–3.23 (m, 4 H, 4 ´ NC(H)H), 3.01 (ddd, J = 8.2, 5.6,

4.3 Hz, 1 H, Hc*), 2.70 (ddd, J = 9.6, 5.6, 4.6 Hz, 1 H, Hd*), 1.70–1.57 (m, 1 H, Hb*), 13 1.25 (s, 3 H, CH3), 0.90–0.83 (m, 1 H, Ha*). C NMR (asterix denotes minor rotamer,

101 MHz, CDCl3) d 166.9 (C=O), 139.5 (Ph-C quat), 134.0 (Ph-C), 129.5 (2 ´ Ph-C),

127.6 (2 ´ Ph-C), 65.3 (NCH2), 65.1 (NCH2) 60.2 (NCH2), 40.4 (C(Hc)), 37.0 (NCH2),

29.7 (CH3), 18.1* (C(Hd)), 17.6 (C(Hd)), 13.4 (C(Ha)(Hb)), 13.1* (C(Ha)(Hb)). HRMS + + (ES) m/z Calcd for C15H21N2O3S [M+H] : 309.1273; Found: 309.1278.

251

(trans)-[2-(Benzenesulfonyl)cyclopropyl](3,4-dihydroquinolin-1(2H)-yl) methanone (138)

O N Hc H Ha d H S b O O

mCPBA (104 mg, 0.60 mmol, 3.0 equiv) was added to a 25 °C solution of amide 87

(62 mg, 0.20 mmol, 1.0 equiv) in CH2Cl2 (10 mL) and the solution stirred for 6 h. Water (30 mL) was added and the phases separated. The aqueous phase was extracted with

Et2O (5 ´ 30 mL). The combined organic phases were washed with brine, dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:2 pentane:Et2O) gave sulfone 138 (67 mg, 98%) as a -1 cream oil. Rf = 0.29 (1:2 pentane:Et2O). IR (film)/cm 3040 (CH), 2950 (CH), 1642 1 (C=O), 1581, 1492, 1402, 1306, 1148, 911, 727. H NMR (400 MHz, CDCl3) d 7.85 (d, J = 7.5 Hz, 2 H, 2 ´ Ph-H), 7.67 (t, J = 7.5 Hz, 1 H, Ph-H), 7.57 (t, J = 7.5 Hz, 2 H, 2 ´ Ph-H), 7.25–7.20 (m, 4 H, 4 ´ Ar-H), 3.80–3.71 (m, 2 H, 2 ´ NC(H)H), 3.14 (ddd, J =

8.6, 5.7, 5.5 Hz, 1 H, Hc), 2.93 (ddd, J = 9.6, 5.7, 4.6 Hz, 1 H, Hd), 2.76–2.63 (m,

2 H, 2 ´ Ar-C(H)H), 2.01–1.86 (m, 2 H, 2 ´ NCH2C(H)H), 1.73 (ddd, J = 8.6, 5.8, 4.6 Hz, 13 1 H, Hb), 1.65–1.63 (m, 1 H, Ha). C NMR (101 MHz, CDCl3) d 168.2 (C=O), 140.1 (Ph-C quat + Ar-C quat), 137.9 (Ar-C quat), 133.7 (Ph-C), 129.4 (2 ´ Ph-C), 128.6

(Ar-C), 127.6 (2 ´ Ph-C), 126.7 (Ar-C), 126.0 (Ar-C), 124.8 (Ar-C), 43.3 (CH2), 41.3

(C(Hc)), 26.7 (CH2), 24.0 (CH2), 20.1 (C(Hd)), 14.2 (C(Ha)(Hb)). HRMS (ES) m/z Calcd + + for C19H20NO3S [M+H] : 342.1164; Found: 342.1174.

252

(cis)-[2-(Benzenesulfonyl)cyclopropyl](4-methylpiperazin-1-yl)methanone (139)

N Hc O H Ha d Hb O S O

mCPBA (28 mg, 0.16 mmol, 3.0 equiv) was added to a 25 °C solution of amide 89

(15 mg, 0.05 mmol, 1.0 equiv) in CH2Cl2 (2.7 mL) and the solution stirred for 6 h. Solid

Na2S2O5 (31 mg, 3.0 equiv) was added and the mixture stirred for 30 min before being concentrated under reduced pressure. The mixture was redissolved in acetone containing 5% Et3N, then filtered. The filtrate was concentrated under reduced pressure then purified by flash column chromatography (3:7 MeOH:CH2Cl2 + 2%

Et3N). The material was dissolved in CH2Cl2, filtered and concentrated under reduced pressure to give sulfone 139 (17 mg, quant) as a golden gum. Rf = 0.29 (3:7 -1 MeOH:CH2Cl2). IR (film)/cm 3032 (CH), 2947 (CH), 1643 (C=O), 1446, 1290 (S=O), 1 1147, 730, 690. H NMR (400 MHz, CDCl3) d 7.90 (m, 2 H, 2 ´ Ph-H), 7.72–7.67 (m, 1 H, Ph-H), 7.62–7.58 (m, 2 H, 2 ´ Ph-H), 4.68–4.64 (m, 1 H, NC(H)H), 4.26–4.22 (m, 2 H, 2 ´ NC(H)H), 3.80–3.76 (m, 2 H, 2 ´ NC(H)H), 3.52–3.48 (m, 1 H, NC(H)H), 3.42

(m, 1 H, NC(H)H), 3.37 (s, 3 H, CH3), 3.35–3.23 (m, 1 H, NC(H)H), 2.83 (ddd, J = 8.6,

8.6, 6.6 Hz, 1 H, Hc), 2.34 (ddd, J = 8.6, 8.6, 7.2 Hz, 1 H, Hd), 1.97 (ddd, J = 7.2, 6.6, 13 6.1 Hz, 1 H, Hb), 1.39 (ddd, J = 8.6, 8.6, 6.1 Hz, 1 H, Ha). C NMR (101 MHz, CDCl3) d 164.1 (C=O), 139.8 (Ph-C quat), 134.0 (Ph-C), 129.5 (2 ´ Ph-C), 127.6 (2 ´ Ph-C),

64.5 (NCH2), 64.3 (NCH2), 59.6 (CH3), 40.4 (NCH2), 40.2 (C(Hc)), 36.6 (NCH2), 23.8 + + (C(Hd)), 11.4 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C15H21N2O3S [M+H] : 309.1273; Found: 309.1270.

253

(trans)-[2-(Benzenesulfonyl)cyclopropyl](3,4-dihydroquinolin-1(2H)-yl) methanone (140)

N Hc O H Ha d H S b O O

mCPBA (78 mg, 0.45 mmol, 3.0 equiv) was added to a 25 °C solution of amide 90

(47 mg, 0.15 mmol, 1.0 equiv) in CH2Cl2 (7.5 mL) and the solution stirred for 6 h. Water (30 mL) was added and the phases separated. The aqueous phase was extracted with

Et2O (5 ´ 30 mL). The combined organic phases were washed with brine, dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (Et2O) gave the sulfone 140 (44 mg, 86%) as a cream gum. -1 Rf = 0.19 (Et2O). IR (film)/cm 3030 (CH), 2934 (CH), 1655 (C=O), 1581, 1491, 1403, 1 1321 (S=O), 1291, 1150 (S=O), 1086, 727. H NMR (400 MHz, CDCl3) d 8.00–7.98 (m, 2 H, 2 ´ Ph-H), 7.63 (t, J = 7.5 Hz, 1 H, Ph-H), 7.57 (t, J = 7.5 Hz, 2 H, 2 ´ Ph-H), 7.16–7.14 (m, 4 H, 4 ´ Ar-H), 4.34 (br s, 1 H, NC(H)H), 3.40 (br s, 1 H, NC(H)H),

2.80–2.70 (m, 3 H, Hc + 2 ´ Ar-C(H)H), 2.41–2.39 (m, 1 H, Hd), 2.18–2.09 (m, 1 H,

NCH2C(H)H), 2.02 (br s, 1 H, Hb), 1.85 (br s, 1 H, NCH2C(H)H), 1.39–1.34 (m, 1 H, 13 Ha). C NMR (101 MHz, CDCl3) d 164.8 (C=O), 140.4 (Ph-C quat + Ar-C quat), 133.9 (Ar-C quat), 133.6 (Ph-C), 129.0 (2 ´ Ph-C), 128.4 (Ar-C), 128.1 (2 ´ Ph-C), 126.0

(Ar-C), 125.5 (Ar-C), 124.2 (Ar-C), 43.6 (CH2), 42.6 (CH2), 26.8 (C(Hc)), 25.6 (C(Hd)), + + 23.8 (CH2), 13.3 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C19H20NO3S [M+H] : 342.1164; Found: 342.1163.

(trans)-Sodium 2-(pyridin-2-yl)cyclopropane-1-carboxylate (141)

O NaO Hc H Ha d Hb N

NaOH(aq) (1.0 M, 0.29 mL, 0.29 mmol, 1.2 equiv) was added to a 30 °C solution of (trans)-ethyl 2-(pyridin-2-yl)cyclopropane-1-carboxylate 134 (46 mg, 0.24 mmol,

254

1.0 equiv) in EtOH (1.2 mL) and the solution was stirred at 30 °C for 24 h. The red reaction mixture was concentrated under reduced pressure, then filtered, washing with acetone (50 mL). The filtrate was concentrated under reduced pressure to give cyclopropane 141 (44 mg, quant) as a red gum. IR (film)/cm-1 1644, 1560 (C=O), 1420, 1 1371. H NMR (400 MHz, DMSO-d6) d 8.36 (d, J = 4.7 Hz, 1 H, Ar-H), 7.59 (dd, J = 7.7, 7.3 Hz, 1 H, Ar-H), 7.21 (d, J = 7.7 Hz, 1 H, Ar-H), 7.08 (dd, J = 7.3, 4.7 Hz, 1 H,

Ar-H), 2.25 (ddd, J = 8.8, 5.4, 5.3 Hz, 1 H, Hc), 1.70 (ddd, J = 8.2, 5.4, 4.1 Hz, 1 H, 13 Hd), 1.21 (ddd, J = 8.2, 5.3, 2.4 Hz, 1 H, Ha), 1.16–1.07 (m, 1 H, Hb). C NMR

(101 MHz, DMSO-d6) d 176.1 (C=O), 161.7 (Ar-C quat), 148.9 (Ar-C), 135.9 (Ar-C),

121.4 (Ar-C), 120.4 (Ar-C), 29.2 (C(Hd)), 25.2 (C(Hc)), 16.2 (C(Ha)(Hb)). HRMS (ES) + + m/z Calcd for C9H10NO2 [M-Na+2H] : 164.0712; Found: 164.0718.

(trans)-[2-(Pyridin-2-yl)cyclopropyl](pyrrolidin-1-yl)methanone (142)

O N Hc H Ha d Hb N

HATU (49 mg, 0.13 mmol, 1.2 equiv) was added to a solution of (trans)-sodium 2- (pyridin-2-yl)cyclopropane-1-carboxylate 141 (20 mg, 0.11 mmol, 1.0 equiv) in N,N-dimethylformamide (540 µL) and the resultant red solution was stirred at 40 °C for 10 min. Pyrrolidine (11 µL, 0.13 mmol, 1.2 equiv) was added and the solution stirred for 20 min. Diisopropylethylamine (56 µL, 0.32 mmol, 3.0 equiv) was added and the solution stirred for 24 h. H2O (10 mL) was added and the mixture extracted with EtOAc (5 ´ 10 mL). The combined organic phases were washed with brine (10 mL), dried

(MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:2 pentane:Et2O) gave cyclopropane 142 -1 (19 mg, 82%) as a yellow gum. Rf = 0.27 (1:2 pentane:Et2O). IR (film)/cm 2954 (CH), 2923 (CH), 2854 (CH), 1741 (C=O), 1596, 1460, 1375, 1220, 964, 803. 1H NMR

(400 MHz, CDCl3) d 8.45 (d, J = 4.4 Hz, 1 H, Ar-H), 7.56 (ddd, J = 7.9, 7.7, 1.5 Hz, 1 H, Ar-H), 7.29 (d, J = 7.9 Hz, 1 H, Ar-H), 7.09–7.06 (m, 1 H, Ar-H), 2.58 (ddd, J =

9.0, 5.5, 4.3 Hz, 1 H, Hc), 2.41 (ddd, J = 8.9, 5.7, 4.3 Hz, 1 H, Hd), 1.58 (ddd, J = 8.9,

255

5.5, 3.4 Hz, 1 H, Ha), 1.48 (ddd, J = 9.0, 5.7, 3.4 Hz, 1 H, Hb), 1.34–1.22 (m, 8 H, 4 ´ 13 CH2). C NMR (101 MHz, CDCl3) d 160.2 (C=O), 149.3 (Ar-C), 135.9 (Ar-C), 125.5

(Ar-C quat), 122.9 (Ar-C), 120.9 (Ar-C), 45.6 (NCH2), 29.7 (NCH2), 25.8 (C(Hc)), 25.3

(C(Hd)), 21.6 (NCH2CH2), 20.7 (NCH2CH2), 17.2 (C(Ha)(Hb)). FTMS (+p NSI) m/z + + Calcd for C13H17N2O [M+H] : 217.1335; Found: 217.1336.

(cis)-Ethyl 2-[1-(benzenesulfonyl)-1H-indol-3-yl]cyclopropane-1-carboxylate (143)

O Hc O H Ha d Hb N O S O

i-PrMgCl (1.20 mL, 1.85 M in THF, 2.25 mmol, 1.5 equiv) was added to a -78 °C solution of (cis)-ethyl 2-(phenylsulfinyl)cyclopropanecarboxylate 97 (358 mg, 1.5 mmol, 1.0 equiv) in THF (15 mL) over 10 s and the solution stirred for 10 min. A mixture of Pd2(dba)3 (35 mg, 0.04 mmol, 2.5 mol%), (t-Bu)3P (17 mg, 0.08 mmol,

5.5 mol%) and ZnCl2 (308 mg, 2.25 mmol, 1.5 equiv) in THF (1.9 mL) was added and the solution stirred at 0 °C for 1 h. A solution of 3-bromo-(1-phenylsulfonyl)indole (1.00 g, 3.00 mmol, 2.0 equiv) in THF (2.0 mL) was added and the reaction stirred at 25 °C for 15 h. MeOH (5 mL) was added and the mixture stirred for 15 min. The mixture was filtered through a pad of silica, washing with CH2Cl2 (200 mL). Concentration under reduced pressure followed by purification by flash column chromatography (5:1 pentane:EtOAc) gave cyclopropane 143 (414 mg, 75%) as a colourless gum. Rf = 0.24 (5:1 pentane:EtOAc). IR (film)/cm-1 3065 (CH), 2931 (CH), 1721 (C=O), 1447, 1366 1 (S=O), 1170 (S=O), 1124, 1092, 980, 734, 684. H NMR (400 MHz, CDCl3) d 7.92 (d, J = 8.2 Hz, 1 H, Ar-H), 7.87–7.84 (m, 2 H, 2 ´ Ar-H), 7.59–7.57 (m, 1 H, Ar-H), 7.52–7.48 (m, 1 H, Ar-H), 7.44–7.40 (m, 3 H, 3 ´ Ar-H), 7.30–7.26 (ddd, J = 7.4, 7.4, 1.3 Hz, 1 H, Ar-H), 7.24–7.20 (ddd, J = 7.4, 7.4, 1.0 Hz, 1 H, Ar-H), 3.78–3.63 (m, 2 H,

CH2CH3), 2.43 (m, 1 H, Hc), 2.18 (ddd, J = 8.8, 8.0, 5.5 Hz, 1 H, Hd), 1.65 (ddd, J =

256

7.2, 5.5, 5.1 Hz, 1 H, Hb), 1.42 (ddd, J = 8.6, 8.0, 5.1 Hz, 1 H, Ha), 0.73 (t, J = 7.1 Hz, 13 3 H, CH3). C NMR (101 MHz, CDCl3) d 170.4 (C=O), 138.1 (Ar-C quat), 135.0 (Ar-C quat), 133.5 (Ar-C), 131.5 (Ar-C quat), 129.1 (2 ´ Ar-C), 126.8 (2 ´ Ar-C), 125.0 (Ar-C), 124.7 (Ar-C), 123.1 (Ar-C), 119.4 (Ar-C), 118.9 (Ar-C quat), 113.6 (Ar-C), 60.1

(CH2CH3), 20.7 (C(Hd)), 15.5 (C(Hc)), 13.7 (CH3), 11.1 (C(Ha)(Hb)). HRMS (ES) m/z + + 1 Calcd for C20H20NO4S [M+H] : 370.1113; Found: 370.1114. The observed data ( H, 13C) was consistent with that previously reported.344

(cis)-{2-[1-(Benzenesulfonyl)-1H-indol-3-yl]cyclopropyl}methanol (144)

HO Hc H Ha d Hb N O S O

Lithium aluminium tetrahydride (1.0 M in THF, 1.35 mL, 1.35 mmol, 2.5 equiv) was added dropwise over 5 min to a 0 °C solution of (cis)-ethyl 2-[1-(benzenesulfonyl)-1H- indol-3-yl]cyclopropane-1-carboxylate 143 (200 mg, 0.54 mmol, 1.0 equiv) in THF (0.68 mL) and the solution stirred at 0 °C for 10 min. The solution was warmed to 25 °C and stirred for 3 h. The reaction mixture was cooled to 0 °C, EtOAc (7 ml) was added and the mixture stirred for 15 min. The mixture was warmed to 25 °C, sat. aq. potassium sodium tartrate (15 mL) was added and the mixture stirred for 1 h. The organic phase was separated, and the aqueous phase extracted with Et2O (5 ´ 10 mL).

The combined organic phases were washed with brine (20 mL), dried (MgSO4), filtered and concentrated under reduced pressure. Purification by flash column chromatography (1:3 pentane:Et2O) gave cyclopropane 144 (166 mg, 94%) as a -1 yellow gum. Rf (Et2O) = 0.44. IR (film)/cm 3387 (OH), 3117 (CH), 3067 (CH), 2923 (CH), 1447, 1366 (S=O), 1173 (S=O), 1124, 1096, 739, 685. 1H NMR (400 MHz,

CDCl3) d 8.00 (d, J = 8.2 Hz, 1 H, Ar-H), 7.86–7.84 (m, 2 H, 2 ´ Ar-H), 7.65 (d, J = 7.7 Hz, 1 H, Ar-H), 7.54 (t, J = 7.4 Hz, 1 H, Ar-H), 7.44 (t, J = 7.7 Hz, 2 H, 2 ´ Ar-H), 7.37–7.33 (m, 1 H, Ar-H), 7.30–7.29 (m, 2 H, Ar-H), 3.51–3.48 (m, 1 H, CH(H)OH),

3.12–3.07 (m, 1 H, CH(H)OH), 2.12–2.06 (m, 1 H, Hd), 1.64–1.55 (m, 1 H, Hc), 1.15

257

(ddd, J = 8.3, 8.3, 5.5 Hz, 1 H, Ha), 0.88 (br s, 1 H, OH), 0.75 (q, J = 5.5 Hz, 1 H, Hb). 13 C NMR (101 MHz, CDCl3) d 138.0 (Ar-C quat), 135.5 (Ar-C quat), 133.8 (Ar-C), 131.7 (Ar-C quat), 129.2 (2 ´ Ar-C), 126.6 (2 ´ Ar-C), 125.2 (Ar-C), 124.0 (Ar-C), 123.6

(Ar-C), 121.1 (Ar-C quat), 119.4 (Ar-C), 113.9 (Ar-C), 62.7 (CH2OH), 19.9 (C(Hc)), 10.8 + + (C(Hd)), 7.6 (C(Ha)(Hb)). HRMS (ES) m/z Calcd for C18H18NO3S [M+H] : 328.1007; Found: 328.1007.

258 Date & Time: 28/04/2015 09:33:18 Chromatogram Name: 64J-E13842-021-355-4-AT1_2 Method Name: 64J-E13842-021-355-4 Operator: AT Group Instrument: SFC MiniGram AT Portal ID: YEL11368-28/04/2015-09:41:51-64J-E13842-021-355-4 Vial Number: 8 Injection Volume: 10.000 ul

Sample Name: 64J-E13842-021-355-4-AT1 4.3. Chiral HPLCColumn: Data AD-H for Enantiopure Cyclopropanes (1S,2R)-15, Mobile Phase: 6% MeOH (no additive) Flow: 5 (ml/min) (1R,2S)-15, (1S,2SPressure:)-16 100 and(bar) (1R,2R)-16 Temperature: 35 (C) Wavelength: 220 (nm)

A. Ethyl (1S,2R)Comments:-2-(phenylsulfanyl) 6% MeOH, AD-H (4.6 x 100mm, -5u)cycloprop ane-1-carboxylate CCP4760.tmp.DAT - Detector 1 Signal (UV)

450

400 0.78

350 EtO O 300

250 Ph S mAU 200

150

100

50 Date & Time: 28/04/2015 09:28:37 Chromatogram0 Name: 64J-E13842-021-355-4-AT2_1 Method Name: 64J-E13842-021-355-4 Operator: AT Group -50 Instrument: SFC MiniGram AT Portal0 ID: YEL11368-28/04/2015-09:42:37-64J-E13842-021-355-41 2 Vial Number: 9 Min Injection Volume: 10.000 ul

Index Time Width 10% Height Area Area [Min] [Min] [mAU] [mAU*min] [%] Sample Name: 64J-E13842-021-355-4-AT21 0.78 0.09 446.59 23.25 100.000 Column: AD-H Mobile Phase: 6%Total MeOH (no additive) 23.25 100.000 Flow: 5 (ml/min) Pressure: 100 (bar) Temperature: 35 (C) Wavelength: 220 (nm) B. Ethyl (1R,2SComments:)-2-(phenylsulfanyl) 6% MeOH, AD-H (4.6 x 100mm, 5u)-cyclopropane -1-carboxylate CCP4761.tmp.DAT - Detector 1 Signal (UV) 0.91 500

450

400

350 EtO O

300

250 Ph S mAU 200

150

100

50 0.78

-50

0 1 2 Min

Index Time Width 10% Height Area Area [Min] [Min] [mAU] [mAU*min] [%] 1 0.78 0.09 8.30 0.40 1.451 2 0.91 0.10 489.30 27.14 98.549 Total 27.54 100.000 Figure 54: Chiral SFC traces for A. ethyl (1S,2R)-2-(phenylsulfanyl)-cyclopropane-1-carboxylate and B. ethyl (1R,2S)-2-(phenylsulfanyl)-cyclopropane-1-carboxylate post-separation. Absolute configurations were determined by X-ray crystallography of the corresponding enantiopure sulfone. Conditions: ADH column, 94:6 CO2:MeOH, flow = 5.0 mL min-1, pressure = 100 bar, temperature = 35 °C, UV detection at 220 nm.

259 Date & Time: 23/04/2015 13:14:25 Chromatogram Name: 64J-E13842-021-355-5-AT1_2_2 Method Name: 64J-E13842-021-355-5 Operator: AT Group Instrument: SFC MiniGram AT Portal ID: YEL11368-23/04/2015-13:18:51-64J-E13842-021-355-5 Vial Number: 39 Injection Volume: 5.000 ul

Sample Name: 64J-E13842-021-355-5-AT1 Column: AD-H Mobile Phase: 8% EtOH (20mM NH3) Flow: 5 (ml/min) Pressure: 100 (bar) Temperature: 35 (C) Wavelength: 220 (nm) A. Ethyl (1S,2S)-2Comments:-(phenylsulfanyl) 8% EtOH + 1% (2M NH3 in MeOH),-cyclopropane AD-H (4.6 x 100mm, 5u) -1-carboxylate CCP3771.tmp.DAT - Detector 1 Signal (UV)

550

500 0.79

450

400 EtO O

350

300 Ph S 250 mAU

200

150

100

Date50 & Time: 23/04/2015 12:50:08 Chromatogram Name: 64J-E13842-021-355-5-AT2_1_2 Method0 Name: 64J-E13842-021-355-5 Operator: AT Group Instrument:-50 SFC MiniGram AT Portal ID: YEL11368-23/04/2015-13:19:17-64J-E13842-021-355-5 0 1 2 Vial Number: 40 Min Injection Volume: 10.000 ul

Index Time Width 10% Height Area Area [Min] [Min] [mAU] [mAU*min] [%] Sample Name: 64J-E13842-021-355-5-AT21 0.79 0.08 539.19 25.65 100.000 Column: AD-H Mobile Phase: 8% EtOH (20mM NH3) Total 25.65 100.000 Flow: 5 (ml/min) Pressure: 100 (bar) Temperature: 35 (C) Wavelength: 220 (nm) B. Ethyl (1R,2R)Comments:-2-(phenylsulfanyl) 8% EtOH + 1% (2M NH3 in MeOH),-cyclopropane AD-H (4.6 x 100mm, 5u) -1-carboxylate CCP3772.tmp.DAT - Detector 1 Signal (UV)

340 1.16 320 300 280 260 240 EtO O 220 200 180 Ph 160 S

mAU 140 120 100 80 60 40

20 0.76 0 -20 -40

0 1 2 Min

Index Time Width 10% Height Area Area [Min] [Min] [mAU] [mAU*min] [%] 1 0.76 0.08 1.60 0.06 0.294 2 1.16 0.12 319.43 21.50 99.706 Total 21.57 100.000 Figure 55: Chiral SFC traces for A. ethyl (1S,2S)-2-(phenylsulfanyl)-cyclopropane-1-carboxylate and B. ethyl (1R,2R)-2-(phenylsulfanyl)-cyclopropane-1-carboxylate post-separation. Absolute configurations were determined by X-ray crystallography of the corresponding enantiopure sulfone. Conditions: ADH column, 92:8 CO2:EtOH + 1% -1 (2 M NH3 in MeOH, flow = 5.0 mL min , pressure = 100 bar, temperature = 35 °C, UV detection at 220 nm.

260

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6. Appendices

6.1. Appendix 1 – Divergent Synthesis of Cyclopropane-Containing Lead-Like Compounds, Fragments and Building Blocks through a Cobalt Catalyzed Cyclopropanation of Phenyl Vinyl Sulfide, S. J. Chawner, M. Cases-Thomas, J. A. Bull, 2017, 34, 5015-5024.

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DOI: 10.1002/ejoc.201701030 Full Paper

Cyclopropanes Divergent Synthesis of Cyclopropane-Containing Lead-Like Compounds, Fragments and Building Blocks through a Cobalt Catalyzed Cyclopropanation of Phenyl Vinyl Sulfide Stephen J. Chawner,[a] Manuel J. Cases-Thomas,[b] and James A. Bull*[a]

Abstract: Cyclopropanes provide important design elements in derivatization is achieved through hydrolysis, reduction, amid- medicinal chemistry and are widely present in drug com- ation and oxidation reactions as well as sulfoxide–magnesium pounds. Here we describe a strategy and extensive synthetic exchange/functionalization. The cyclopropyl Grignard reagent studies for the preparation of a diverse collection of cyclo- formed from sulfoxide exchange is stable at 0 °C for > 2 h, propane-containing lead-like compounds, fragments and build- which enables trapping with various electrophiles and Pd-cata- ing blocks exploiting a single precursor. The bifunctional cyclo- lyzed Negishi cross-coupling reactions. The library prepared, as propane (E/Z)-ethyl 2-(phenylsulfanyl)-cyclopropane-1-carb- well as a further virtual elaboration, is analyzed against parame- oxylate was designed to allow derivatization through the ester ters of lipophilicity (ALog P), MW and molecular shape by using and sulfide functionalities to topologically varied compounds the LLAMA (Lead-Likeness and Molecular Analysis) software, to designed to fit in desirable chemical space for drug discovery. illustrate the success in generating lead-like compounds and A cobalt-catalyzed cyclopropanation of phenyl vinyl sulfide af- fragments. fords these scaffolds on multigram scale. Divergent, orthogonal

Introduction significantly lower.[6] Hence, attractive screening collections can offer significant value. Considerable effort has been expended A limitation in examining new, challenging pharmaceutical tar- in developing guidelines to describe and influence compound gets is the availability of innovative, novel fragments and build- collections, which are frequently used to aid in the developing blocks that possess desirable physicochemical properties, ment of a compound, aiming to predispose derivatives to fall [1] and sample new regions of chemical space. Recent years have into regions of desirable chemical space.[3a,7] Relevant parame- seen a focus on smaller, more polar compounds and less planar, ters of interest include lipophilicity (Log P), molecular weight sp3-rich derivatives containing fewer aromatic rings, perceived (MW), number of rotatable bonds, polar surface area (PSA) and to be more likely to successfully progress through drug devel- the numbers of hydrogen-bond donors and acceptors (HBD/ [2,3] opment. New synthetic strategies and methods can enable HBA), and consideration of these has given rise to the terms chemical space to be probed more effectively by enriching cur- drug-like, lead-like and fragment to describe screening com- rent lead-like and fragment compound libraries with compounds.[7,8] pounds that can present new design elements and novel bond The cyclopropane motif is highly significant in drug discov- [1,4,5] vectors. ery as the 10th most frequently found ring system in small mol- Late-stage compound attrition, particularly within phase II ecule drugs.[9,10] It is also present in a variety of biologically and phase III clinical trials, is extremely costly to the drug dis- active natural products and other medicinally-important mol- covery industry, with the cost of ensuring appropriate molec- ecules (Figure 1).[11,12] Substituted cyclopropanes present a ular properties at a much earlier stage of development being well-defined 3-dimensional shape, conformational rigidity, and electronic properties in between that of an alkene and a gem- [a] Department of Chemistry, Imperial College London, dimethyl group, for example, as a result of the small strained South Kensington, London SW7 2AZ, UK ring structure. E-mail: [email protected] The synthesis of cyclopropane derivatives has been exten- http://www3.imperial.ac.uk/people/j.bull sively investigated, exploiting numerous powerful synthetic [b] Lilly Research Centre, Eli Lilly and Company, [13] Erl Wood Manor, Sunninghill Road, Windlesham, methods (Figure 2a). Cyclopropanes bearing functional Surrey, GU20 6PH, UK groups have been generated through Simmons–Smith cyclo- Supporting information and ORCID(s) from the author(s) for this article are propanation,[14,15] transition metal-catalyzed carbene insertion available on the WWW under https://doi.org/10.1002/ejoc.201701030. to alkenes using diazo compounds,[16,17] and the reaction of © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This sulfur ylides with electron deficient alkenes.[18] Furthermore, the is an open access article under the terms of the Creative Commons Attribu- tion License, which permits use, distribution and reproduction in any cross-coupling of cyclopropyl organometallic or (pseudo)halide medium, provided the original work is properly cited. species has been exploited as a more divergent approach to

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propane derivatives. As such we targeted small bifunctional cyclopropane-containing scaffolds (Figure 2b). Here we report the development of (E)- and (Z)-ethyl 2- (phenylsulfanyl)-cyclopropane-1-carboxylate as cyclopropane scaffolds and extensive studies on the bidirectional functionalization. Derivatization of these scaffolds affords a collection of lead-like and fragment compounds as well as further building blocks for the preparation of cyclopropane derivatives. High- lights include a cobalt-catalyzed cyclopropanation of phenyl vinyl sulfide, formation of amido-cyclopropyl sulfones, and generation of cyclopropyl Grignard reagent through sulfoxide– metal exchange followed by reaction with various electrophiles and use in Pd-catalyzed Negishi cross-coupling reactions. Fi- nally, we present analysis on the physicochemical properties and molecular shape of the compounds prepared, to illustrate that these scaffolds afford medicinally relevant, non-planar compounds that occupy desirable chemical space.

Results and Discussion Figure 1. Selected cyclopropane-containing natural products and pharmaceutical compounds. Scaffold Design and Hypothesis cyclopropane derivatives through functionalization of the We envisaged that a wide variety of medicinally-relevant cyclo- ring.[19] Most recently this has been extended to include power- propane-containing compounds could be prepared in a diver- ful C–H functionalization methods.[20] gent manner from a single central bifunctional cyclopropyl scaffold. For this we required a low molecular weight scaffold that could be easily derivatized to lead-like compounds or fragments, and functionalized in two directions, ideally through bond formation to the cyclopropane ring itself. The two scaffold functionalities should undergo derivatization orthogonally, granting access to a wide and diverse scope of functionality on the ring. We considered (E)- and (Z)-ethyl 2-(phenylsulfanyl)- cyclopropane-1-carboxylates would meet these criteria, and provide suitable building blocks through functionalization of the ester or sulfide groups (Figure 2c). Especially valuable would be the potential to convert the sulfide to the sulfoxide and exploit sulfoxide–magnesium exchange to form bonds directly to the cyclopropane ring.[21–23] Both the E- and Z-diastereoisomers were of interest, possessing very different bond vectors, to increase the shape diversity of the compounds. Hence, the first objective was to prepare these building blocks on a large scale.

Cyclopropanation of Phenyl Vinyl Sulfide

To generate cyclopropyl scaffolds 1 and 2 we envisaged the reaction of phenyl vinyl sulfide (PVS) with ethyl diazoacetate (EDA) in a transition metal-catalyzed cyclopropanation

Figure 2. Strategies for the synthesis of cyclopropanes and designed bifunc- (Scheme 1). The only prior report of the cyclopropanation of tional cyclopropane building blocks. PVS with EDA was in 1962; an uncatalyzed reaction requiring heating of the neat reactants at 100 to 170 °C in a sealed ves- We proposed that a divergent route to cyclopropane con- sel.[24–26] In search of less hazardous, lower temperature reac- taining lead-like compounds and fragments would present a tion conditions suitable for multi-gram scale, transition metal valuable approach to a novel screening collection. Furthermore, catalysts were investigated. Initially complexes of Pd0,Rh0,CuI this approach would provide interesting building blocks that and CuII were explored for catalytic activity (see the Supporting may be more generally applicable for the construction of cyclo- Information for further details).

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try 6) or on water, which gave quantitative yield (Entry 7). Both E- and Z-products were formed in approximately equal amounts providing both diastereoisomers for further functionalization, as was desired for a divergent strategy. Excellent yields were observed both for the reaction without

solvent or run on H2O, up to a 10 mmol scale (Table 1, entries 6–8, 10). However, when the neat cyclopropanation was carried out at scales greater than 10 mmol, an exotherm was observed with concomitant gas evolution and a significant decrease in yield (Table 1, entry 9). This was not observed when the reaction was carried out on water, and under these conditions reac- Scheme 1. Proposed synthesis of E- and Z-cyclopropyl scaffolds. tion on a 40 mmol scale afforded excellent yields without indi- cation of a significant increase in temperature. Purification and separation of the diastereoisomers was facile on smaller scales, but on larger scale, separation of a catalyst From the initial screening, only CuIOTf (0.5 mol-%) promoted derived impurity became problematic. This was resolved the reaction effectively, and a yield of up to 54 % was obtained through modification of the work-up procedure: bubbling air by running the reaction in CHCl at 30 °C with a slow addition 3 through a diluted reaction mixture oxidized the remaining CoII of the diazo compound. A mixture of trans and cis substituted catalyst to a putative CoIII–peroxo-bridged dimer[28] which was cyclopropanes were formed in a 1:1 ratio. These were readily simply removed by filtration through a pad of silica. The rate of separated to single diastereoisomers. However, the relatively CoII oxidation was highly dependent on the diluent due to dif- low yield and exacting practical considerations detracted from ferent oxygen permeability, dissolution capability and coordi- the reaction convenience and this approach was not suitable nating effects of the solvents, with isohexane performing best for scale-up. Pleasingly on further investigation, CoII–(salen)- (see the Supporting Information for further details).[29] This pro- type complex 3 was found to catalyze the desired cyclopropan- tocol, diluting the reaction with isohexane then bubbling air ation (Scheme 1).[17,27] The use of 5 mol-% of the CoII complex, through the solvent for 15 min followed by filtration through in CH Cl at 40 °C gave 40 % yield in 24 h (Table 1, entry 1). As 2 2 silica, enabled facile removal of the catalyst and derived impuri- has been observed with other Co-catalyzed cyclopropanation ties and then separation of the diastereoisomers by flash chro- reactions using diazo compounds,[17] the reactions were facile matography. Approximately 4 g of each separated diastereo- to set up and the catalyst was easily stored and did not result isomer was readily formed in a single run (Table 1, entry 11). in dimerization of the diazo reagent under the reaction condi- The enantiomers of both diastereoisomers were also readily tions, removing the need for a slow addition protocol. separated by preparative chiral supercritical fluid chromatography (SFC) to afford all four possible stereoisomers, each in Table 1. Effect of solvent and reaction scale on the CoII-catalyzed cyclopropanation reaction.

Entry[a] Solvent dr Yield 1 + 2 (trans 1/cis 2)[b] [%][c]

1 CH2Cl2 52:48 40 2 CHCl3 48:52 13 3 toluene 45:55 53 4 benzene 48:52 73 5 TBME 48:52 69 6 neat 46:54 93

7H2O 47:53 100 8[d] Neat 53:47[e] 70[f] 9[g] Neat 52:48[e] 46[f] [d] [e] [f] 10 H2O 45:55 85 [h] [e] [f,i] 11 H2O 46:54 89 [a] Reaction conditions: EDA (0.3 mmol); PVS. (1.5 equiv.), catalyst 3 (5 mol- %), solvent, 40 °C, 24 h. [b] Calculated from the crude reaction mixture by 1H NMR unless stated otherwise. [c] Yields were calculated using 1H NMR by comparison with an internal standard (dibenzyl ether) unless stated otherwise. [d] 10 mmol scale. [e] dr from isolated masses. [f] Combined yield of separated isolated products. [g] 20 mmol scale. [h] 40 mmol scale. [i] Corre- sponds to 7.9 g of product (1 + 2).

To optimize the promising CoII-catalyzed reaction a solvent screen was conducted (Table 1). Cyclopropanes 1 and 2 were Figure 3. Enantiomerically pure cyclopropyl sulfides were obtained by prepar- observed under each set of conditions tested (Entries 1–7), but ative chiral SFC and analysed by X-ray crystallography of the corresponding the reaction was most efficient in the absence of a solvent (En- sulfones.

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≥ 97 % ee. Whereas the sulfides were oils, the corresponding tions used for hydrolysis above, the reaction mixture was evap- cyclopropyl sulfones (vide infra) were crystalline. Absolute con- orated to form the carboxylate salt in quantitative yield, which figurations and structural confirmation of the sulfones and was itself characterized. This was applied directly in a HATU- hence precursor sulfides was proven through single-crystal X- promoted amidation reaction to form a series of amides 14a– ray diffraction analysis (Figure 3).[30] 14d from trans-cyclopropane 1, and 15a–15d from cis-2. Such This separation approach provided highly enantioenriched motifs are widely found in biologically active molecules (for ex- compounds 1 and 2, hence granting access to each derivative ample see Figure 1). A selection of the resulting cyclopropyl as a single enantiomer. As an alternative approach to generate amides was oxidized to the corresponding sulfones to generate the enantioenriched cyclopropane derivatives, chiral CuI and further interesting compounds with desirable physicochemical CoII catalysts were investigated (see the Supporting Information properties for drug discovery (16c,d and 17c,d). For compounds for further details). Enantioenriched catalyst 3 afforded moder- 16c and 17c, aqueous work-up proved problematic due to high ate ee values for both the trans and cis compounds (52 % ee 1 water solubility. This issue was overcome by an aqueous-free and 77 % ee 2, in H2O at 20 °C, 57 % overall yield). However, work-up. Excess mCPBA was quenched by the addition of solid this was not the focus of this study, and for the derivatization Na2S2O5 to the reaction, which was followed by removal of the reactions presented below the racemate was used to form a reaction solvent, redissolution in acetone containing 5 % Et3N racemic screening set. and filtration. Under this procedure, after collection of the filtrate, all mCPBA derived materials had been removed, providing the sulfones in excellent purity and yield. All of the transformations described were achieved without any epimerization to the Sulfide Oxidation and Ester Functionalization corresponding diastereoisomers, as indicated by 1H NMR (Scheme 3). With a practical, high yielding and scalable route to cyclopropyl scaffolds 1 and 2, functionalization of the sulfide and ester groups was examined. Oxidation of the sulfide to the sulfone was readily achieved in quantitative yield using excess mCPBA (Scheme 2). This provided a short route to the functionalized cyclopropyl sulfone derivatives as single diastereoisomers, themselves interesting motifs in biologically active compounds.[31,32] Using 1 equiv. mCPBA at 0 °C gave sulfoxides 6 and 7 in high yields as a mixture of diastereoisomers at sulfur,[33,34] and as important compounds for our envisaged sulfoxide exchange strategy.

Scheme 3. Synthesis of amide-substituted cyclopropanes through amidation and oxidation. Yields for 14/15 quoted over 2 steps from 1/2.

Scheme 2. Scaffold derivatization by oxidation, reduction or hydrolysis.

Stability and Reactions of Cyclopropylmagnesium The ethyl ester was readily hydrolyzed to the carboxylic acid Reagents Generated by Sulfoxide–Magnesium Exchange using sodium hydroxide, for both diastereoisomers (Scheme 2).

Alternatively, reduction with LiAlH4 gave the primary alcohol- A key aspect of our approach was that for increased diversity, cyclopropyl sulfide in high yields. To form the cyclopropyl the position of the sulfur group should be functionalizable, amides, the cyclopropyl carboxylate salt was reacted directly, through its removal, in order to form bonds directly to the cy- using a method described by Batey.[35] Under the same condi- clopropyl ring. We intended to utilize cyclopropyl sulfoxides,

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Full Paper and a sulfoxide–metal exchange strategy to allow functionalization of the anion. Sulfoxide–metal exchange has been used to generate three- membered ring organometallics, in the form of cyclopropanes,[21,36] aziridines,[22] and epoxides,[23] for reaction with limited examples of reactive electrophiles or protonation. Knochel has previously reported halogen–metal exchange to generate cis-[2-(ethoxycarbonyl)-cyclopropyl]magnesium chloride,[37,38] comparable to the Grignard reagent that would be generated from 2 by sulfoxide–magnesium exchange. In the Knochel work, coordination between the ester and the Lewis acidic magnesium atom was proposed. Therefore, we concentrated our efforts on optimizing the exchange for the trans-derivative, where such a potentially stabilizing interaction would not be possible. Early investigation of this reaction showed that iPrMgCl formed the putative cyclopropyl Grignard reagent 18 from cyclopropane 6 efficiently at –78 °C, also generating isopropyl phenyl sulfoxide. Trapping the intermediate using I2 gave cyclopropyl iodide 19a as a single trans-diastereoisomer. Impor- tantly, the reaction proceeded with retention of configuration for both the E- and the Z-cyclopropyl sulfoxides.[39] To maximize the reactivity of the organometallic species while avoiding degradation, we assessed both the time required for the exchange to go to completion, and the stability of the cyclopropyl Grignard intermediate species. Sulfoxide– magnesium exchange reactions were conducted on cyclopropane 6 using iPrMgCl and iPrMgCl·LiCl,[40] trapping with molecular iodine at –78 °C after different time periods (Figure 4a). This study led to several observations i) the exchange was complete in 10 min, ii) the cyclopropyl Grignard reagent was stable for at least 2 hours at –78 °C prior to the addition of the Figure 4. a) The effect of using iPrMgCl or iPrMgCl·LiCl on the stability of the electrophile, and iii) similar yields were obtained for the reac- cyclopropyl organometallic intermediate after various exchange periods. b) tions using iPrMgCl and iPrMgCl·LiCl at each time point, indicat- The effect of temperature on the stability of the cyclopropyl organometallic ing the addition of LiCl did not provide an advantage. Next, we intermediate after various incubation periods. investigated the thermal stability of the Grignard intermediate by conducting the sulfoxide–magnesium exchange with iPrMgCl at –78 °C (10 min), then incubating the reaction mixture at either –30, 0 or 25 °C for different time periods, prior to one (19h). Trapping with phenyl isocyanate generated the trapping at this temperature (Figure 4b). Pleasingly, the cyclo- cyclopropyl amide (19i) and trapping with a disulfide gave the propyl intermediate was stable for over 2 h at temperatures up corresponding cyclopropyl sulfide (19j). Finally, a series of po- to 0 °C. However, at 25 °C significant decomposition was ob- tential cyclopropane building-blocks were prepared. Trapping served, which corresponded to a reduction of product yield by with N,N-dimethylformamide allowed access to the cyclopropyl half after approximately 45 min of incubation, and <25 % yield aldehyde in an excellent yield (19k), an isopropoxy dioxaborol- after 2 h. Following this study, various electrophiles were inves- ane generated the corresponding cyclopropyl boronic ester tigated, trapping at 0 °C to maximize the reactivity. Both the E- (19l) and trapping with chlorotriethoxysilane produced the tri- and the Z-cyclopropyl sulfoxides could be trapped efficiently ethoxysilylcyclopropane (19m). The Grignard reagent originat- with I2 to generate cyclopropanes 19a and 20a (Scheme 4). ing from the Z-cyclopropyl sulfoxide could also be trapped with With these exchange conditions in hand, a wide range of a similar series of electrophiles, generating diversely substituted electrophiles were examined, intending to generate varied cis-cyclopropanes. Interestingly, it was observed that with cer- cyclopropane containing structures (Scheme 4). The Grignard tain aldehyde and ketone electrophiles initial electrophilic at- reagent 18 originating from E-cyclopropyl sulfoxide 6 could be tack was followed by lactonization to generate the bicyclic trapped efficiently with aliphatic, aromatic and heteroaromatic product. Complete lactonization was observed to generate 20b, aldehydes in excellent yields (19b–19d). Dialkyl, diaryl and di- 20c and 20f, whereas alcohol 20g was the major product with heteroaryl ketones also proceeded in good to excellent yields the dipyridyl ketone electrophile. (19e–19g). Electrophilic trapping of the cyclopropyl Grignard Next we explored a sulfoxide–magnesium exchange–Negishi was observed with benzoyl chloride to give the cyclopropyl ket- cross-coupling protocol to form (hetero)aryl cyclopropanes

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Scheme 5. Substrate scope for the sulfoxide–magnesium exchange–Negishi cross-coupling protocol.

insertion to alkenes. It is notable that Lewis basic sites on electron-poor heterocycles as well as electron-rich heterocycles can present difficulties in other cyclopropane strategies, hence heteroaromatic bromides were investigated. Both electron-poor and electron-rich heterocycles could be readily incorporated to give pyridine, pyrimidine and indole cyclopropane derivatives 21e–21g respectively. cis-Cyclopropyl sulfoxide 7 also successfully underwent sulfoxide–magnesium exchange–Negishi cross- coupling with a bromoindole to generate cis-cyclopropane 22h. Finally, we chose to further elaborate compounds 21e and 22h through the remaining ester functionality (Scheme 6). From pyridyl cyclopropane 21e, hydrolysis to give the E-cyclopropyl Scheme 4. Scope of electrophiles for the sulfoxide–magnesium exchange, carboxylate sodium salt 23 followed by amidation with pyrrol- electrophilic trap protocol. [a] Trapping with I2. [b] From the corresponding idine gave the corresponding cyclopropyl amide 24 in an 82 % aldehyde. [c] From the corresponding ketone. [d] Using benzoyl chloride. [e] yield as a relatively complex yet low molecular weight frag- Using phenylisocyanate. [f] Using bis(4-methoxyphenyl)disulfide. [g] Using ment. Similarly, reduction of indole-cyclopropyl ester 22h to DMF [h] Using (pin)BOiPr. [i] Using (EtO)3SiCl. the primary alcohol 25 proceeded in a 94 % yield. Both 24 and 25 presented structural features related to biologically active [12c] which are important pharmacophores. There are no prior compounds shown in Figure 1, and were rapidly accessed as examples of cross-coupling between aryl halides and cyclo- interesting fragment and lead-like motifs. propyl organometallics derived from cyclopropyl sulfoxides.[21c] We employed a protocol similar to that which we recently reported for aziridine sulfoxides,[22e] and were delighted to observe the successful Negishi cross-coupling from both trans and cis-cyclopropane derivatives with aryl bromides (Scheme 5). The same sulfoxide–magnesium exchange protocol as developed above was used to generate the intermediate cyclopropyl

Grignard reagent. A mixture of Pd2(dba)3,(tBu)3P and ZnCl2 Scheme 6. Synthesis of bifunctional cyclopropanes by utilizing both synthetic (1.5 equiv.) in THF was added and the mixture stirred for1hat handles. 0 °C followed by the addition of the aryl bromide (2 equiv.). The coupling of bromobenzene proceeded at 25 °C over 15 h to give cyclopropanes 21a and 22a in excellent yields. Using Fragment and Lead-Likeness Analysis the trans-cyclopropyl sulfoxide, 1-bromo-4-chlorobenzene and 2-bromoanisole both gave high yields of the aryl-cyclopropanes The cyclopropane-containing compounds prepared in this 21b and 21c respectively. Cross-coupling with !-bromostyrene study were designed to possess desirable physicochemical gave an excellent yield of the corresponding vinyl cyclopropane properties and sample new areas of chemical space for medici- 21d, which would be challenging to form through carbenoid nal chemistry.[41,42] To illustrate the success of this approach the

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Full Paper library was assessed against parameters of Alog P vs. MW, and the set of compounds possess varied 3-dimensional structures, molecular shape through a principal moments of inertia (PMI) sampling chemical space away from the planar rod-like–disk- plot,[43] calculated using the Lead-likeness and Molecular Analy- like axis (Figure 6). The different 3-dimensional structures of sis (LLAMA) software, developed by Nelson and Marsden.[41] All the E- and Z-diastereoisomers are exemplified by three sets of compounds prepared in this study were included with the ex- compounds highlighted. ception of those considered reactive building blocks (iodides The powerful LLAMA software also executes virtual elabora- 19a and 20a, aldehyde 19k, pinacol boronates 19l and 20l, tion of the molecular scaffolds and calculates the physicochemi- and ethoxysilane 19m).[44] The molecular properties of the 50 cal properties of the resulting compounds.[41] This indicates the included compounds were shown to explore efficiently lead- potential of scaffolds to generate a much wider array of lead- like and fragment space (Figure 5). like or drug-like compounds through elaboration by common reactions used in medicinal chemistry. The 56 cyclopropanes prepared in this study, including this time those compounds intended as building blocks, were examined as scaffolds in this program. Given the presence of ester functionality in several of the compounds in our study, a slight modification of default decoration inputs was applied, by the addition of an ester hydrolysis reaction option. Using the default set of 44 reactants within LLAMA, and permitting up to 2 reactions on the scaffolds, 1187 cyclopropane-containing compounds were generated.[45] Of these, 392 examples had a molecular weight less than 300 and 1033 examples had a molecular weight less than 500, indicative of fragment and drug-like space respectively. A PMI plot of the decorated compounds shows that the full set Figure 5. The relationship between ALog P and MW for compounds prepared. of elaborated compounds displayed highly varied topologies, and were significantly removed from the often over-populated The PMI plot generated from the normalized ratios of princi- region along the rod-like–disk-like axis (see Graph S2 in the pal moments of inertia calculated through LLAMA, showed that Supporting Information).[45]

Figure 6. PMI plot showing the shape distribution of the synthesized compounds. Some examples have been selected to illustrate the difference between the E- and Z-diastereoisomers.

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Conclusions added the reaction vessel was sealed with either a crimp seal microwave vial lid with a septum, or a suba seal and the reaction vessel

In conclusion, we have developed a strategy for preparing a flushed with Ar(g).Ar(g) flushed, deflated balloons were attached to diverse range of cyclopropane-containing fragments, lead-like the flask, so that the total potential volume of the balloons when compounds and building blocks from a readily accessible cyclo- inflated was greater than the volume of N2(g) evolved from the reac- propyl scaffold. An operationally facile and scalable CoII-cata- tion. On scales where ≥ 10 mmol of diazo compound were used, a lyzed cyclopropanation of phenyl vinyl sulfide was developed precautionary blast shield was placed between the reaction flask to prepare the bifunctional cyclopropyl scaffold. Divergent, or- and the fume hood sash. thogonal derivatization of the scaffold has been demonstrated Supporting Information (see footnote on the first page of this through hydrolysis, amidation, reduction and oxidation reac- article): Further details can be found in Supporting Information. tions, as well as sulfoxide–magnesium exchange protocols. In- vestigations into the stability of the cyclopropyl Grignard spe- Acknowledgments cies have led to successful trapping with a broad scope of electrophiles. A sulfoxide–magnesium exchange–Negishi cross-cou- For financial support, we gratefully acknowledge The Royal So- pling protocol enables (hetero)aryl rings to be installed directly ciety [University Research Fellowship (to J. A. B.), and URF Ap- onto the intact cyclopropane ring. Finally, we have presented pointed Grant], the Engineering and Physical Sciences Research the calculated physicochemical properties of the synthesized Council (EPSRC) [CAF to J. A. B. (EP/J001538/1), and Impact Ac- compounds and of potential derivatives which supports their celeration Account (EP/K503733/1)]. We thank Eli Lilly (UK) and value as potential screening compounds. Imperial College London for studentship funding (to S. J. C.). We acknowledge the EPSRC National Mass Spectrometry Facility, Swansea. Thanks to Daniel O'Reilly for early investigation into Experimental Section ester hydrolysis/amidation. Our special thanks to Benjamin A. Diseroad for the X-ray derived structures and Craig White and General Experimental Considerations: All non-aqueous reactions his analytical and separation sciences team. were run under an inert atmosphere (argon) with flame-dried glassware using standard techniques. Anhydrous solvents were obtained by filtration through drying columns (THF, CH2Cl2, toluene, DMF). Keywords: Cyclopropanes · Sulfoxides · Small ring systems · Where applicable, room temp. denotes a room temperature of ap- Homogeneous catalysis · Molecular diversity proximately 22 °C, and a specifically noted temperature e.g. “stirred at 25 °C” indicates the stated temperature was accurately maintained. Flash column chromatography was performed using 230– [1] a) C. W. Murray, D. C. Rees, Angew. Chem. Int. Ed. 2016, 55, 488–492; 400 mesh silica with the indicated solvent system according to stan- Angew. Chem. 2016, 128, 498; b) F. W. Goldberg, J. G. Kettle, T. Kogej, dard techniques. Analytical thin-layer chromatography (TLC) was M. W. D. Perry, N. P. Tomkinson, Drug Discovery Today 2015, 20, 11–17. performed on precoated, glass-backed silica gel plates. Visualization [2] a) F. Lovering, J. Bikker, C. Humblet, J. Med. Chem. 2009, 52, 6752–6756; b) F. Lovering, Med. Chem. Commun. 2013, 4, 515–519; c) T. J. Ritchie, of the developed chromatogram was performed by UV absorbance S. J. F. 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