DOCSLIB.ORG

Regioselectivity in the Ene Reaction of Singlet Oxygen with Alkenes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Regioselectivity in the Ene Reaction of Singlet Oxygen with Alkenes TETRAHEDRON Pergamon Tetrahedron 56 (2000) 1595–1615 Tetrahedron Report Number 519 Regioselectivity in the Ene Reaction of Singlet Oxygen with Alkenes Manolis Stratakis and Michael Orfanopoulos* Department of Chemistry, University of Crete, Iraklion 71409, Greece Dedicated to Professor C. S. Foote on the occasion of his 65th birthday Received 4 October 1999 Contents 1. Introduction 1595 2. Regioselectivity of the Ene Reaction 1596 2.1. ‘cis Effect’ with trisubstituted alkenes and enol ethers 1596 2.2. syn Stereoselectivity with allylic alcohols 1597 2.3. Anti ‘cis effect’ selectivity 1597 2.4. Phenyl group directing syn selectivity 1598 2.5. Regioselectivity with cis and trans disubstituted alkenes. The large group non-bonded effect 1598 2.6. Regioselectivity with geminal dimethyl and diethyl trisubstituted alkenes 1599 2.7. Geminal regioselectivity with respect to a bulky allylic substituent 1600 2.8. The role of non-bonded interactions between the cis alkyl substituents during the formation of the new double bond in the ene adduct 1603 2.9. Geminal selectivity with vinylsilanes and vinylstannanes 1603 2.10. Regioselectivity with allylic silanes, stannanes and germanes 1604 2.11. Regioselectivity with olefins bearing an electron withdrawing group at the a-position 1605 2.12. Regioselectivity with olefins bearing an electron withdrawing group at the b-position, and with homoallylic alcohols. The role of electronic repulsions 1605 2.13. Regioselectivity with twisted 1,3-dienes. Vinylic versus allylic hydrogen reactivity 1607 2.14. Regioselectivity in the autooxidation of fullerene adducts 1607 2.15. Regioselectivity of the ene photooxygenation reaction within zeolites 1607 3. Solvent Effects in the Ene Regioselectivity 1608 4. Synthetic Transformations of Regioselective and Stereoselective Ene Reactions 1609 5. Conclusions 1610 1. Introduction 1953,13 and it was revived after the pioneering work of Foote14 in the early 1960s. Ever since, amongst all singlet 1 The chemistry of singlet molecular oxygen ( O2) has oxygen reactions, it has attracted major interest due to its received remarkable attention by chemists not only because controversial reaction mechanism and fascinating regio- of its interesting mechanistic and synthetic aspects1–4 but chemistry and stereochemistry. also because of its large environmental5–7 and biomedical significance.8–10 Among the peculiar types of reaction In the past a great deal of work has been focused on whether 1 involving O2 with organic substrates are: [412], ene, and the ene reaction proceeds through a concerted or a stepwise [212] additions to alkenes and oxidation of organic mechanism. The initially proposed synchronous pathway15 compounds of sulfur, phosphorus, etc. The ene reac- was challenged by biradical,16 zwitterionic,17 or perepox- tion2,3,11,12 was originally discovered by Schenck in ide11 intermediates (Scheme 1). Kinetic isotope effects in the photooxygenation of tetrasubstituted,18 trisubstituted19 20 * Corresponding author. Tel.: 130-81-393630; fax: 130-81-393601; and cis alkenes supported the irreversible formation of 21,22 e-mail: [email protected] an intermediate perepoxide, while for trans alkenes, a 0040–4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S0040-4020(99)00950-3 1596 M. Stratakis, M. Orfanopoulos / Tetrahedron 56 (2000) 1595–1615 2,3-dihydro-g-pyran and suggested the importance of an initial orbital interaction between the incoming oxygen and the enol ether. Stephenson47 suggested that an inter- action between the LUMO orbital of the oxygen and the HOMO orbital of the olefin stabilizes the transition state of perepoxide formation. This is particularly true for the case of cis-2-butene where the bonded orbitals of the allylic hydrogen contribute to the HOMO orbital of the olefin, thus generating a system similar to the c 3 state of butadiene. The p Scheme 1. interaction of this system with the p LUMO orbital of the oxygen is favorable. For the trans isomer the contribution of the bonded orbitals of the allylic C–H bonds to the HOMO partial equilibration of the intermediate with the reactants orbital of the olefin is approximately half, thus making the was proposed. Consistent with the perepoxide intermediate interaction with the oxygen LUMO less favorable. is also the observation that the ene reaction proceeds as a highly suprafacial process, in which the conformational For a cycloalkene48 it was proposed that there is a correla- arrangement of the allylic hydrogen controls the stereo- tion between the orientation of the allylic hydrogen in the chemistry of the allylic hydroperoxide produced.23 ground state and its reactivity. The allylic hydrogens at the axial position are more reactive, because the orbital overlap Trapping of the intermediate with sulfoxides,24 phos- between oxygen and allylic hydrogens is optimum in such a phites,25 and sulfenates or sulfinate esters,26 in the photo- conformation. oxygenation of adamandylidenoadamantane, and theoretical calculations27–31 as well, support the perepoxide In 1981 Houk and coworkers,49 using STO-EG semi- as the most possible intermediate. Many authors consider an empirical calculations, suggested that for acyclic alkenes intermediate exciplex32–34 instead of the polar perepoxide. differences in regioselectivity are related to the different Since the geometry of the intermediate is well defined from energies required for an allylic hydrogen to adopt a perpen- isotope effects and stereochemical studies, if an inter- dicular arrangement to the olefinic plane. For example, in mediate exciplex is formed, its geometrical features must cis-2-butene the rotational barrier of an allylic hydrogen to resemble those of a perepoxide. adopt a perpendicular alignment to the double bond plane from an eclipsed conformation was calculated to be In the photooxygenation of electron rich alkenes like 1.06 kcal/mol, while for the trans isomer it is higher by enamines,35 enol ethers,36 enol esters37 and dienes,38–40 1 kcal/mol. This assumption was in accordance with the there is a partitioning between perepoxide and zwitterionic experimental observation that cis alkenes react about intermediates, affording mixtures of ene and cycloaddition 10–20 times faster than their trans isomers.50 products, whose relative abundance depends on solvent polarity and temperature. Schuster and coworkers51,52 measured the activation para- ‡ ‡ 1 meters DH and DS in the ene reaction of O2 with a series of alkenes and suggested that there is a type of ‘hydrogen 2. Regioselectivity of the Ene Reaction bonding’ interaction in the rate-limiting step of perepoxide formation between the allylic hydrogens and the intermedi- 2.1. ‘cis Effect’ with trisubstituted alkenes and enol ate. For example, in the reaction of cis-2-butene activation ethers entropy DS‡ is less negative by 10 e.u., than that of the corresponding trans isomer, while the activation enthalpies 1 41,42 ‡ In the reaction of O2 with trisubstituted alkenes and DH are very similar. The considerable difference in the enol ethers,43,44 the more reactive side of the double bond activation entropies was attributed to the fact that transition is the more substituted. This surprising selectivity is referred states in the cases of cis olefins require more organization to as the ‘cis effect’ (Table 1). Both experimental and because of the simultaneous interaction of the incoming theoretical chemists have offered explanations for the ‘cis oxygen with two allylic hydrogens as seen in the accompa- effect’. Bartlett and Frimer45,46 studied the primary and nying scheme. On the other hand for trans alkenes, this secondary isotope effects in the photooxygenation of interaction occurs with only one allylic hydrogen. Table 1. Numbers indicate percentage of double bond formation in the ene adducts M. Stratakis, M. Orfanopoulos / Tetrahedron 56 (2000) 1595–1615 1597 Table 2. syn/anti Selectivity in the photooxygenation of allylic alcohols 9-E crowded side to form PEI, the oxygen interacts simul- and 9-Z taneously with the hydroxyl and one allylic hydrogen. This interaction stabilizes the transition state. Polar solvents interact with the hydroxyl through hydrogen bonding and reduce its ability to interact with the oxygen. Thus, the ‡ activation energy of TSI increases significantly and leads Substrate Solvent syn/anti Selectivity to a reversal of selectivity which is now controlled by steric factors. The observed stereoselectivity in methanol 9-E CCl4 75:25 (syn/anti 33:67) is a typical example of anti ‘cis effect’ 9-E Benzene 73:27 behavior, similar to that observed in the sterically analogous 9-E CH3CN 41:59 9-E MeOH 33:67 substrates 10-E and 10-Z (see accompanying Section 2.3). 9-Z CCl4 72:28 9-Z CH3CN 40:60 2.3. Anti ‘cis effect’ selectivity The proposal that there is a stabilizing effect by the simul- It can be concluded that most of the proposed explanations 1 taneous interaction of O2 with two allylic hydrogens on the are consonant with the existence of an interaction between same side of the olefin during the formation of the perep- the incoming oxygen and two allylic hydrogens that highly oxide, suffices to explain the rare cases where anti ‘cis stabilizes the transition state of perepoxide formation. effect’ selectivity has been observed in the photooxygena- tion of the series of acyclic trisubstituted alkenes59 shown in 2.2. syn Stereoselectivity with allylic alcohols Table 3. Recently, Adam and coworkers, in order to explain the high For these substrates, the less substituted side of the double diastereoselectivity (d.e. ,90%) observed in the photo- bond is the more reactive. In the case of alkenes 10-E and oxygenation of chiral allylic alcohols53,54 and amines,55,56 10-Z, for example, formation of the perepoxide on the more proposed that singlet oxygen forms an exciplex with the substituted side of the olefin is not favorable because of allylic alcohol, in which the oxygen coordinates to the steric repulsions between the oxygen and the two alkyl hydroxyl.
Load more

Recommended publications
  • Elimination Reactions E1, E2, E1cb and Ei
    Elimination Reactions Dr. H. Ghosh Surendranath College, Kol-9 ________________________________________________ E1, E2, E1cB and Ei (pyrolytic syn eliminations); formation of alkenes and alkynes; mechanisms (with evidence), reactivity, regioselectivity (Saytzeff/Hofmann) and stereoselectivity; comparison between substitution and elimination. Substitution Reactions Elimination Reactions Elimination happens when the nucleophile attacks hydrogen instead of carbon Strong Base favor Elimination Bulky Nucleophile/Base favor Elimination High Temperature favors Elimination We know- This equation says that a reaction in which ΔS is positive is more thermodynamically favorable at higher temperature. Eliminations should therefore be favoured at high temperature Keep in Mind---- Mechanism Classification E1 Mechanism- Elimination Unimolecular E1 describes an elimination reaction (E) in which the rate-determining step is unimolecular (1) and does not involve the base. The leaving group leaves in this step, and the proton is removed in a separate second step E2 Mechanism- Elimination Bimolecular E2 describes an elimination (E) that has a bimolecular (2) rate-determining step that must involve the base. Loss of the leaving group is simultaneous with removal of the proton by the base Bulky t-butoxide—ideal for promoting E2 as it’s both bulky and a strong base (pKaH = 18). Other Organic Base used in Elimination Reaction These two bases are amidines—delocalization of one nitrogen’s lone pair on to the other, and the resulting stabilization of the protonated amidinium ion, E1 can occur only with substrates that can ionize to give relatively stable carbocations—tertiary, allylic or benzylic alkyl halides, for example. E1-Elimination Reaction not possible here The role of the leaving group Since the leaving group is involved in the rate-determining step of both E1 and E2, in general, any good leaving group will lead to a fast elimination.
    [Show full text]
  • Transparent Photochemistry: Infrared Photosensitizers and Singlet Oxygen Microscopy
    Transparent Photochemistry: Infrared photosensitizers and singlet oxygen microscopy Elsa Fernanda Freitas da Silva Tese orientada por: Luís Guilherme da Silva Arnaut Moreira e Peter Remsen Ogilby Universidade de Coimbra Tese de Doutoramento em Química, especialidade Fotoquímica apresentada ao Departamento de Química da Faculdade de Ciências e tecnologia da Universidade de Coimbra. Coimbra, Julho de 2013 Acknowledgements This dissertation is the result of joint efforts, collaborations and help by many people. I want to express my appreciation to my supervisor, Professor Luis G. Arnaut, for his guidance, support and availability. His enthusiasm with science and motivation are an example to me. It has been a great pleasure to work in his group. To my group of colleagues in Coimbra: Rui Nunes, Gonçalo Sá, Ligia Silva, Hélder Tão, I want to thank you all for the support and fellowship. Specially, I want to thank Carlos Serpa for his availability to help and assistance me with the laser systems and, Fábio Schaberle for his assistance with photoacoustic calorimetry experiments and for been actively interested on my work providing me with great comments that were valued greatly. My special thanks to Professor Peter R. Ogilby for accepting to be my co-supervisor and give me the opportunity to work with different techniques in his laboratory in the University of Aarhus in Denmark. Peter valuable suggestions have greatly improved my scientific work. I have had a great time working in COMIs group. I want to thank all COMI group members whom I have encountered during my stay, for their great support and welcoming. Brian Wett for walking me through the laboratory on my first times.
    [Show full text]
  • States of Oxygen Liquid and Singlet Oxygen Photodynamic Therapy
    Oxygen States of Oxygen As far as allotropes go, oxygen as an element is fairly uninteresting, with ozone (O3, closed-shell and C2v symmetric like SO2) and O2 being the stable molecular forms. Most of our attention today will be devoted to the O2 molecule that is so critically connected with life on Earth. 2 2 2 4 2 O2 has the following valence electron configuration: (1σg) (1σu) (2σg) (1πu) (1πg) . It is be- cause of the presence of only two electrons in the two π* orbitals labelled 1πg that oxygen is paramagnetic with a triplet (the spin multiplicity \triplet" is given by 2S+1; here S, the total spin quantum number, is 0.5 + 0.5 = 1). There are six possible ways to arrange the two electrons in the two degenerate π* orbitals. These different ways of arranging the electrons in the open shell are called \microstates". Further, because there are six microstates, we can say that the total degeneracy of the electronic states 2 3 − arising from (1πg) configuration must be equal to six. The ground state of O2 is labeled Σg , the left superscript 3 indicating that this is a triplet state. It is singly degenerate orbitally and triply degenerate in terms of spin multiplicity; the total degeneracy (three for the ground state) is given by the spin times the orbital degeneracy. 1 The first excited state of O2 is labeled ∆g, and this has a spin degeneracy of one and an orbital degeneracy of two for a total degeneracy of two. This state corresponds to spin pairing of the electrons in the same π* orbital.
    [Show full text]
  • The Photochemistry of Tetramethyl-3-Thio-1,3-Cyclobutanedione
    South Dakota State University Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange Electronic Theses and Dissertations 1972 The Photochemistry of tetramethyl-3-thio-1,3-cyclobutanedione Mason Ming-Sun Shen Follow this and additional works at: https://openprairie.sdstate.edu/etd Recommended Citation Shen, Mason Ming-Sun, "The Photochemistry of tetramethyl-3-thio-1,3-cyclobutanedione" (1972). Electronic Theses and Dissertations. 4833. https://openprairie.sdstate.edu/etd/4833 This Thesis - Open Access is brought to you for free and open access by Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. For more information, please contact [email protected]. THE PHarOCHEMISTRY OF TETRAMETHYL-3-THIO-l,J-CYCLOBUTANEDIONE BY MASON MING-SUN SHEN A thesis submitted in partial fulfillment of the requirements for tne degree Master of Science, Major - in Chemistry, South Dakota State University 1972 SOUTH DAKOTA STATE UNIVERSITY LIBRAR fer -th:Ls -7 - - -- -07 -­ D;;;/:...; TO MY PARENTS PHOTOCHEMISTRY OF THE TETRAMETHYL-)-THI0-1,)-CYCLOBUTANEDIONE Abstract MASON MING-SUN SHEN Under the supervision of Professor James J. Worman photochemical reaction of tetramethyl-3-thio-i.l,3-cyclo­ The butanedione in the presence of oxygen and light yields tetramethyl-1, )-cyclobutanedione and sulfur dioxide. kinetics and mechanism of the reaction have been studied The thoroughly in different solvents and at different concentrations. Results this study indicate that the mechanism probably involves· of singlet oxygen and state thione although triplet thione and ground triplet xygen are not completely eliminated.
    [Show full text]
  • Electrochemistry and Photoredox Catalysis: a Comparative Evaluation in Organic Synthesis
    molecules Review Electrochemistry and Photoredox Catalysis: A Comparative Evaluation in Organic Synthesis Rik H. Verschueren and Wim M. De Borggraeve * Department of Chemistry, Molecular Design and Synthesis, KU Leuven, Celestijnenlaan 200F, box 2404, 3001 Leuven, Belgium; [email protected] * Correspondence: [email protected]; Tel.: +32-16-32-7693 Received: 30 March 2019; Accepted: 23 May 2019; Published: 5 June 2019 Abstract: This review provides an overview of synthetic transformations that have been performed by both electro- and photoredox catalysis. Both toolboxes are evaluated and compared in their ability to enable said transformations. Analogies and distinctions are formulated to obtain a better understanding in both research areas. This knowledge can be used to conceptualize new methodological strategies for either of both approaches starting from the other. It was attempted to extract key components that can be used as guidelines to refine, complement and innovate these two disciplines of organic synthesis. Keywords: electrosynthesis; electrocatalysis; photocatalysis; photochemistry; electron transfer; redox catalysis; radical chemistry; organic synthesis; green chemistry 1. Introduction Both electrochemistry as well as photoredox catalysis have gone through a recent renaissance, bringing forth a whole range of both improved and new transformations previously thought impossible. In their growth, inspiration was found in older established radical chemistry, as well as from cross-pollination between the two toolboxes. In scientific discussion, photoredox catalysis and electrochemistry are often mentioned alongside each other. Nonetheless, no review has attempted a comparative evaluation of both fields in organic synthesis. Both research areas use electrons as reagents to generate open-shell radical intermediates. Because of the similar modes of action, many transformations have been translated from electrochemical to photoredox methodology and vice versa.
    [Show full text]
  • Reactions of Alkenes and Alkynes
    05 Reactions of Alkenes and Alkynes Polyethylene is the most widely used plastic, making up items such as packing foam, plastic bottles, and plastic utensils (top: © Jon Larson/iStockphoto; middle: GNL Media/Digital Vision/Getty Images, Inc.; bottom: © Lakhesis/iStockphoto). Inset: A model of ethylene. KEY QUESTIONS 5.1 What Are the Characteristic Reactions of Alkenes? 5.8 How Can Alkynes Be Reduced to Alkenes and 5.2 What Is a Reaction Mechanism? Alkanes? 5.3 What Are the Mechanisms of Electrophilic Additions HOW TO to Alkenes? 5.1 How to Draw Mechanisms 5.4 What Are Carbocation Rearrangements? 5.5 What Is Hydroboration–Oxidation of an Alkene? CHEMICAL CONNECTIONS 5.6 How Can an Alkene Be Reduced to an Alkane? 5A Catalytic Cracking and the Importance of Alkenes 5.7 How Can an Acetylide Anion Be Used to Create a New Carbon–Carbon Bond? IN THIS CHAPTER, we begin our systematic study of organic reactions and their mecha- nisms. Reaction mechanisms are step-by-step descriptions of how reactions proceed and are one of the most important unifying concepts in organic chemistry. We use the reactions of alkenes as the vehicle to introduce this concept. 129 130 CHAPTER 5 Reactions of Alkenes and Alkynes 5.1 What Are the Characteristic Reactions of Alkenes? The most characteristic reaction of alkenes is addition to the carbon–carbon double bond in such a way that the pi bond is broken and, in its place, sigma bonds are formed to two new atoms or groups of atoms. Several examples of reactions at the carbon–carbon double bond are shown in Table 5.1, along with the descriptive name(s) associated with each.
    [Show full text]
  • Organic Chemistry-I (Nature of Bonding and Stereochemistry
    Subject Chemistry Paper No and Title 1; Organic Chemistry-I (Nature of bonding and Stereochemistry Module No and 25; Regioselectivity Title Module Tag CHE_P1_M25 CHEMISTRY Paper No. 1: Organic Chemistry-I (Nature of bonding and Stereochemistry Module no. 25: Regioselectiveity TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction 2.1 Different Examples of Regioselective Reactions 2.1.1 Regioselectivity in Addition Reactions 2.1.2 Addition of HBr to Alkenes 2.1.3 Hydroboration Reaction and Addition of Hydrogen and Bromine to Alkenes 2.1.4 Baeyer Villiger Oxidation 2.1.5 Birch Reduction 2.1.6 Electrophilic Aromatic Substitution 2.1.7 Diels Alder Reaction 2.1.8 Friedal Crafts Reaction 2.1.9 Regioselectivity of Elimination 2.2 How to Determine the Regioselectivity? 3. Summary CHEMISTRY Paper No. 1: Organic Chemistry-I (Nature of bonding and Stereochemistry Module no. 25: Regioselectiveity 1. Learning Outcomes After studying this module, you shall be able to Know what is regioselectivity. Understand the basic difference between regioselectivity and chemoselectivity. Identify the regioselectivity in various reactions. Calculate the regioselectivity for a particular reaction. 2. Introduction 2. What is Regioselectivity? Regioselectivity is known as the preference chemical bond breaking or making in one direction of over all other possible directions. It is certainly applicable to positions which many reagents affect during the course of the reaction. An example to consider is which proton a strong base will abstract from an organic molecule, or where on a substituted benzene ring a further substituent will add. If there occurs a preponderance over which regioisomer will be formed, then that reaction can be termed as regioselective.
    [Show full text]
  • Intramolecular Ene Reactions of Functionalised Nitroso Compounds
    INTRAMOLECULAR ENE REACTIONS OF FUNCTIONALISED NITROSO COMPOUNDS A Thesis Presented by Sandra Luengo Arratta In Partial Fulfilment of the Requirements for the Award of the Degree of DOCTOR OF PHILOSOPHY OF UNIVERSITY COLLEGE LONDON Christopher Ingold Laboratories Department of Chemistry University College London 20 Gordon Street London WC1H 0AJ July 2010 DECLARATION I Sandra Luengo Arratta, confirm that the work presented in this thesis is my own. Where work has been derived from other sources, I confirm that this has been indicated in the thesis. ABSTRACT This thesis concerns the generation of geminally functionalised nitroso compounds and their subsequent use in intramolecular ene reactions of types I and II, in order to generate hydroxylamine derivatives which can evolve to the corresponding nitrones. The product nitrones can then be trapped in the inter- or intramolecular mode by a variety of reactions, including 1,3-dipolar cycloadditions, thereby leading to diversity oriented synthesis. The first section comprises the chemistry of the nitroso group with a brief discussion of the current methods for their generation together with the scope and limitations of these methods for carrying out nitroso ene reactions, with different examples of its potential as a powerful synthetic method to generate target drugs. The second chapter describes the results of the research programme and opens with the development of methods for the generation of functionalised nitroso compounds from different precursors including oximes and nitro compounds, using a range of reactants and conditions. The application of these methods in intramolecular nitroso ene reactions is then discussed. Chapter three presents the conclusions which have been drawn from the work presented in chapter two, and provides suggestions for possible directions of this research in the future.
    [Show full text]
  • [4 + 2] Annulation and Enyne Cross Metathesis
    Communication pubs.acs.org/JACS Gold-Catalyzed Intermolecular Reactions of Propiolic Acids with Alkenes: [4 + 2] Annulation and Enyne Cross Metathesis † † † ‡ ‡ ‡ Hyun-Suk Yeom, Jaeyoung Koo, Hyun-Sub Park, Yi Wang, Yong Liang, Zhi-Xiang Yu,*, † and Seunghoon Shin*, † Department of Chemistry and Research Institute for Natural Sciences, Hanyang University, Seoul 133-791, Korea ‡ Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering, College of Chemistry, Peking University, Beijing 100871, China *S Supporting Information Scheme 1. Propiolic Acid as a Functional Equivalent of 1,4- ABSTRACT: A gold-catalyzed intermolecular reaction of C,O-Dipole or Biscarbene propiolic acids with alkenes led to a [4 + 2] annulation or enyne cross metathesis. The [4 + 2] annulation proceeds with net cis-addition with respect to alkenes and provides an expedient route to α,β-unsaturated δ-lactones, for which preliminary asymmetric reactions were also demonstrated. For 1,2-disubstituted alkenes, unprecedented enyne cross metathesis occurred to give 1,3-dienes in a completely stereospecific fashion. DFT calculations and experiments indicated that the cyclobutene derivatives are not viable We commenced our study using propiolic acid (4a) and intermediates and that the steric interactions during 10 concerted σ-bond rearrangements are responsible for the styrene derivatives as substrates. After extensive optimization, observed unique stereospecificity. we found that treating styrene 3a with 4a
    [Show full text]
  • Appendix I: Named Reactions Single-Bond Forming Reactions Co
    Appendix I: Named Reactions 235 / 335 432 / 533 synthesis / / synthesis Covered in Covered Featured in problem set problem Single-bond forming reactions Grignard reaction various Radical couplings hirstutene Conjugate addition / Michael reaction strychnine Stork enamine additions Aldol-type reactions (incl. Mukaiyama aldol) various (aldol / Claisen / Knoevenagel / Mannich / Henry etc.) Asymmetric aldol reactions: Evans / Carreira etc. saframycin A Organocatalytic asymmetric aldol saframycin A Pseudoephedrine glycinamide alkylation saframycin A Prins reaction Prins-pinacol reaction problem set # 2 Morita-Baylis-Hillman reaction McMurry condensation Gabriel synthesis problem set #3 Double-bond forming reactions Wittig reaction prostaglandin Horner-Wadsworth-Emmons reaction prostaglandin Still-Gennari olefination general discussion Julia olefination and heteroaryl variants within the Corey-Winter olefination prostaglandin Peterson olefination synthesis Barton extrusion reaction Tebbe olefination / other methylene-forming reactions tetrodotoxin hirstutene / Selenoxide elimination tetrodotoxin Burgess dehydration problem set # 3 Electrocyclic reactions and related transformations Diels-Alder reaction problem set # 1 Asymmetric Diels-Alder reaction prostaglandin Ene reaction problem set # 3 1,3-dipolar cycloadditions various [2,3] sigmatropic rearrangement various Cope rearrangement periplanone Claisen rearrangement hirstutene Oxidations – Also See Handout # 1 Swern-type oxidations (Swern / Moffatt / Parikh-Doering etc. N1999A2 Jones oxidation
    [Show full text]
  • Steam Cracking: Chemical Engineering
    Steam Cracking: Kinetics and Feed Characterisation João Pedro Vilhena de Freitas Moreira Thesis to obtain the Master of Science Degree in Chemical Engineering Supervisors: Professor Doctor Henrique Aníbal Santos de Matos Doctor Štepánˇ Špatenka Examination Committee Chairperson: Professor Doctor Carlos Manuel Faria de Barros Henriques Supervisor: Professor Doctor Henrique Aníbal Santos de Matos Member of the Committee: Specialist Engineer André Alexandre Bravo Ferreira Vilelas November 2015 ii The roots of education are bitter, but the fruit is sweet. – Aristotle All I am I owe to my mother. – George Washington iii iv Acknowledgments To begin with, my deepest thanks to Professor Carla Pinheiro, Professor Henrique Matos and Pro- fessor Costas Pantelides for allowing me to take this internship at Process Systems Enterprise Ltd., London, a seven-month truly worthy experience for both my professional and personal life which I will certainly never forget. I would also like to thank my PSE and IST supervisors, who help me to go through this final journey as a Chemical Engineering student. To Stˇ epˇ an´ and Sreekumar from PSE, thank you so much for your patience, for helping and encouraging me to always keep a positive attitude, even when harder problems arose. To Prof. Henrique who always showed availability to answer my questions and to meet in person whenever possible. Gostaria tambem´ de agradecer aos meus colegas de casa e de curso Andre,´ Frederico, Joana e Miguel, com quem partilhei casa. Foi uma experienciaˆ inesquec´ıvel que atravessamos´ juntos e cer- tamente que a vossa presenc¸a diaria´ apos´ cada dia de trabalho ajudou imenso a aliviar as saudades de casa.
    [Show full text]
  • Hydrocarbons Thermal Cracking Selectivity Depending on Their Structure and Cracking Parameters
    Master in Chemical Engineering Hydrocarbons Thermal Cracking Selectivity Depending on Their Structure and Cracking Parameters Thesis of the Master’s Degree Development Project in Foreign Environment Cláudia Sofia Martins Angeira Erasmus coordinator: Eng. Miguel Madeira Examiner in FEUP: Eng. Fernando Martins Supervisor in ICT: Doc. Ing Petr Zámostný July 2008 Acknowledgements I would like to thank Doc. Ing. Petr Zámostný for the opportunity to hold a master's thesis in this project, the orientation, the support given during the laboratory work and suggestions for improvement through the work. i Hydrocarbons Thermal Cracking Selectivity Depending on Their Structure and Cracking Parameters Abstract This research deals with the study of hydrocarbon thermal cracking with the aim of producing ethylene, one of the most important raw materials in Chemical Industry. The main objective was the study of cracking reactions of hydrocarbons by means of measuring the selectivity of hydrocarbons primary cracking and evaluating the relationship between the structure and the behavior. This project constitutes one part of a bigger project involving the study of more than 30 hydrocarbons with broad structure variability. The work made in this particular project was focused on the study of the double bond position effect in linear unsaturated hydrocarbons. Laboratory experiments were carried out in the Laboratory of Gas and Pyrolysis Chromatography at the Department of Organic Technology, Institute of Chemical Technology, Prague, using for all experiments the same apparatus, Pyrolysis Gas Chromatograph, to increase the reliability and feasibility of results obtained. Linear octenes with different double bond position in hydrocarbon chain were used as model compounds. In order to achieve these goals, the primary cracking reactions were studied by the method of primary selectivities.
    [Show full text]