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Investigations into Aryne Chemistry Alastair Alexander Cant A thesis submitted in part fulfilment of the requirements of the degree of Doctor of Philosophy Department of Chemistry College of Science and Engineering University of Edinburgh August 2011 Abstract The first project in this thesis describes our research reacting arynes with tertiary allyl amines to generate functionalised anilines via a benzyne induced aza-Claisen reaction. This process works in good to excellent yields and the methodology can be further applied to make benzannulated medium sized ring amine systems. The second project covered in this thesis details our studies in the generation of benzyne from benzoic acid. This process utilises palladium catalysis involving an ortho C-H activation of benzoic acid which generates a 5 membered palladacycle. This palladacycle then spontaneously decomposes with heat to generate palladium bound benzyne and carbon dioxide. The yield of benzyne was monitored by observing the amount of triphenylene formed in the process. Further synthetic applications in this process were limited, but it was shown that the benzyne could be reacted with alkynes to generate phenanthrene and naphthalene products. The third project in this thesis details our work on the insertion of benzyne into the C–S bond of thioesters. Using palladium catalysis and an o-trimethylsilylphenyl triflate benzyne precursor, a variety of thioethers were produced. The yields for this reaction were moderate to good but it was found that only aromatic substituents were tolerated on the thioester. i" " Contents Abstract i Contents ii Acknowledgement v Author’s Declaration vi Abbreviations vii 1 Introduction 1 1.1 Methods of Generating Arynes 1 1.2 The Organometallic Capture and Generation of Arynes 4 1.3 Organometallic Methods for Generating Arynes 6 1.4 Transition Metal Catalysed Aryne Reactions. 9 1.4.1 Palladium Catalysed Three Component Couplings of Benzyne 9 1.4.2 Intramolecular Three Component Couplings 14 1.4.3 Aryne Annulations Coupled With C–H Activation 17 1.4.4 Palladium Catalysed [2+2+2] Cycloadditions 19 1.5 The Use of Other Metal Catalysts in Aryne Chemistry 22 1.5.1 A Nickel Catalysed Method for Aryne Generation 22 1.5.2 Three Component Couplings of Benzyne 23 1.5.3 Metal Mediated Nucleophilic Additions to Arynes. 26 1.5.4 A Nickel Catalysed [2+2+2] Cycloaddition 27 ii" " 1.6 Conclusion 29 2 The Benzyne Aza-Claisen Reaction 30 2.1 Reaction Optimisation 32 2.2 Exploring the Scope 35 2.3 Side Reactions 44 2.4 Possible Extensions of Chemistry 47 2.4.1 Exploring Other Substrates 47 2.4.2 Novel Reactions With Propan-2-one Derivatives 48 2.4.3 A 1,3-Sigmatropic Shift 50 2.4.4 A Diels-Alder Reaction With 2-Vinylpyridine 51 2.5 Conclusions 52 3 Generation of Benzyne From Benzoic Acid Using C–H Activation 53 3.1 Reaction Optimisation 57 3.2 Exploring the Scope of Benzoic Acids 67 3.3 Exploring the Mechanism of Benzyne Formation from Benzoic Acid 71 3.3 Reacting Benzyne Derived From Benzoic Acid 72 3.4 Conclusions 81 4 The Insertion of Benzyne into Thioesters 82 4.1 Reaction Optimisation 84 4.2 Exploring the Scope of the Reaction 89 iii" " 4.3 Investigating the Decarbonylative Reaction 92 4.4 Aryne Insertion into Esters 93 4.5 Conclusions 93 5 Other Projects 94 5.1 A Benzyne Ene Reaction 94 5.1.1 Results and Discussion 95 5.1.2 Conclusions 97 6 Experimental 98 6.1 General Experimental Data 98 6.2 Experimental Data for the Benzyne Aza-Claisen Reaction 100 6.3 Experimental Data for the Generation of Benzyne from Benzoic Acid 124 6.4 Experimental Data for the Insertion of Benzyne into Thioesters 139 6.5 Experimental Data for Ene Reaction 151 7 References 153 Appendix A 160 Appendix B 162 iv" " Acknowledgements Firstly, I would like to say a huge thank you to my supervisor, Dr Michael Greaney for giving me the opportunity to study in his research group. His help, support and the continuous fountain of ideas throughout the course of my PhD have been much appreciated. I would also like to acknowledge Lee Roberts from Pfizer for his insightful ideas into the chemistry and for making my three month CASE placement at Pfizer an enjoyable and productive experience. Thank you to all the staff at Edinburgh University who have provided technical support: Derek Burgess, John Knox, Raymond Borwick and Tim Calder, Juraj and Marika for assistance with NMR and David for his help with mass spec. Thanks to Alex, Naim, Stephan, Donnie, Jaclyn, Laura, Kallol, Feng-Zhi, Venu, Didier and Lee for sharing this experience with me and for making it an enjoyable one. A big thank you also goes to Mark, Fiona, Adele, Lynne, Lorna and the rest of the Sutherland group for teaching me the difference between a hyphen and a dash and making me feel welcome in a new home. Financial support from the Engineering and Physical Sciences Research Council (EPSRC), Cancer Research UK and Pfizer is also gratefully acknowledged. Finally I would like to thank my family for their love and support throughout my PhD. My mum and dad for encouraging me to always aim higher, my wife, Claire for her unending patience through 9 years of studentship and my daughter Sophie for making us laugh every day. v" " Author’s Declaration This thesis represents the original work of Alastair Alexander Cant unless explicit reference is made to the contribution of others in the text. The research was carried out in the Joseph Black Building at the University of Edinburgh under the supervision of Dr Michael F. Greaney. Portions of the work described herein have been published elsewhere as listed below: A. A. Cant, G. H. V. Bertrand, J. L. Henderson, L. Roberts, M. F. Greaney, Angew. Chem. Int. Ed. 2009, 48, 5199-5202. A. A. Cant, L. Roberts, M. F. Greaney, Chem. Commun., 2010, 8671-8673. vi" " Abbreviations °C degrees celcius µL microlitre µmol micromoles Ac acetyl Ar aryl BINAP 2,2'-bis(diphenylphosphino)-1,1'-binapthyl Boc tert-butoxycarbonyl bpt boiling point Bu butyl cod cyclooctadiene Cy cyclohexyl dba dibenzylideneacetone DCM dichloromethane DMAc dimethylacetylene DMAD dimethylacetylenedicarboxylate DME ethylene glycol dimethyl ether DMF dimethylformamide DMSO dimethylsulfoxide dppb 1,4-bis(diphenylphosphino)butane dppe 1,2-bis(diphenylphosphino)ethane dpph 1,2-bis(diphenylphosphino)hexane dppm 1,1-bis(diphenylphosphino)methane ee enantiomeric excess equiv. equivalents Et ethyl EWG electron withdrawing group g grams GCMS gas chromatography mass spectrometry vii" " h hours HMDS hexamethyldisilazane iPr isopropyl JACS Journal of the American Chemical Society L ligand/litre LDA lithium diisopropylamine M Molar Me methyl MeCN acetonitrile mL millilitre mmol millimoles mol moles mpt melting point MS molecular seives NMP N-methylpyrrolidinone NMR nuclear magnetic resonance spectroscopy No. number O/N overnight Ph phenyl ppm parts per million PTC phase transfer catalyst rac racemic RB round bottomed RT room temperature SIMes 2,4,6-trimethylphenyl TBAB tetra-n-butylammonium bromide TBAC tetra-n-butylammonium chloride TBAI tetra-n-butylammonium iodide TBAT tetra-n-butylammonium difluorotriphenylsilicate tBu tertiary butyl viii" " TCC three component coupling Temp temperature Tf triflouromethane sulfonate TFA trifluoroacetic acid THF tetrahydrofuran TLC thin layer chromatography TMS trimethylsilyl tol toluene triflate trifluoromethane sulfonate ix" " 1 Introduction 1.1 Methods of Generating Arynes The organic chemist now has access to a vast selection of methods for the generation of arynes, all of which have both pros and cons to their use. This introduction will detail some of the more popular methods for the generation of arynes as well as reviewing some of the more contemporary methods recently developed. The first recorded evidence of arynes was published by the German scientists Stoermer and Khalert in 1902.[1] They found that when 3-bromobenzofuran was treated with strong base in ethanol they yielded 2-ethoxybenzofuran as product. This product was unexpected as the expected SNAr mechanism should yield only the 3- ethoxy-derivative. This anomaly was recorded, but was not fully explained and it was only later that aryne intermediacy was proposed as a mechanism to explain the unusual regiochemistry of these reactions.[2] Fig. 1.1.1. The reaction of 3-bromobenzofuran with potassium hydroxide and ethanol. This method of aryne generation is well developed and involves the use of strong bases to ortho-deprotonate halo aromatics such as 2 which then decompose to give benzyne (figure 1.1.2.). It is a firmly established route to o-benzyne and there are numerous examples in the literature of its use.[3-7] Over the years numerous new methods were developed to generate arynes in addition to the method discovered by Stoermer and Khalert. Some of the more popular classical methods for generating arynes are detailed in figure 1.1.2. 1 Fig. 1.1.2.