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Download (6MB) STUDIES ON THE GENERATION AND REACTIVITY OF METAL CARBENOIDS A Thesis Presented by Rehan Aqil In Partial Fulfilment of the Requirements for the Award of the Degree of DOCTOR OF PHILOSOPHY OF THE UNIVERSITY OF LONDON Christopher Ingold Laboratories Department of Chemistry University of London London WCIH OAJ September 2002 ProQuest Number: U643094 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest U643094 Published by ProQuest LLC(2015). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Abstract ABSTRACT This thesis concerns the generation of metal carbenoids, in particular organozinc carbenoids, and their subsequent reactions, such as C-H insertion reactions or cyclopropanation with alkenes. The thesis is divided into three major sections. The introductory chapter presents a comparative review covering metal carbenoid species. The review focuses on how their reactivity is controlled by the metal, the leaving group and by the nature of electron-donating and -withdrawing groups on the carbenoid and finally which type of alkenes give the highest reactivity and yields as a function of these parameters. The results and discussion chapter opens with a brief overview of the organozinc carbenoid chemistry which has been developed within our group. Subsequent sections then describe a range of reactions which were investigated. Thus, studies on both the acid catalysed chlorotrimethylsilane-zinc deoxygenation of ketones and the use of iodotrimethylsilane-zinc for reactive carbenoid generation are presented and used in an investigation of transannular insertion in small, medium and large ring sized ketones. The first efforts towards electrochemical generation of organozinc carbenoids for dicarbonyl coupling are then described. This is followed by a detailed study of the regio- and stereoselective behaviour of electron rich dienes with a range of organozinc carbenoids generated from appropriate aldehydes and ketones. An investigation of both zinc and copper carbenoids in carboalkoxy- cyclopropanations is then presented. In addition, the generation of a novel geminally substituted alkoxy-carboalkoxy copper carbenoid was also examined and used for cyclopropanation. Attempts to generate metal carbenoids from halo iminium salts for aminocylopropanation are also discussed. This is followed by a chapter summarising the results achieved and perspectives for future work. A concluding chapter provides a formal description of the experimental results and procedures together with appropriate references. Contents CONTENTS Abstract 1 Contents 2 Acknowledgements 6 Abbreviations 7 Chapter 1. Introduction 10 1. The Generation and Reactivity of Metal Carbenoids 11 1.1 Carbenes and Carbenoids 13 1.2 Methylene Carbenoids [YMCH 2 X] 14 1.2.1 Zinc Carbenoids 14 1.2.1.1 The Evolution of Simmons Smith Carbenoids 15 1.2.1.2 The “Furukawa” Modification 17 1.2.1.3 (Chloromethyl)zinc v (lodomethyl)zinc Carbenoid Species 18 1.2.1.4 The Reactivity of Bromomethylzinc Bromide [BrZnCH2Br] 22 1.2.1.5 The Effect of the Y Group on the Reactivity in Functionalised Halomethylzinc Carbenoids [YZnCHzX] 24 1.2.1.6 The Effect of the Leaving Group X on the Reactivity in Functionalised Methylene Zinc Carbenoids [YZnCH 2 X] 32 1.2.1.7 A Direct Comparison of Various Methylene Zinc Carbenoids 35 1.2.2 Cadmium Carbenoids 37 1.2.3 Mercury Carbenoids 38 1.2.4 Copper Carbenoids 41 1.2.5 Samarium Carbenoids 42 1.2.6 Aluminium Carbenoids 46 1.2.7 Indium Carbenoids 49 1.2.8 Lithium Carbenoids 49 1.2.9 Magnesium Carbenoids 51 Contents 1.3 Alkyl and Aryl Mono- and Di-Substituted Carbenoids 51 1.3.1 Methyl- and Phenyl-Substituted Carbenoids [YMCH(R)X] 52 1.3.2 Dimethylmethylene Carbenoids [YMC(CH3 )2 X] 55 1.3.3 Geminal Dizinc Carbenoids [(RZn) 2 CHI] 58 1.3.4 Cbloro-Alkyl and -Aryl Zinc Carbenoids 59 1.3.5 Magnesium Carbenoids 60 1.4 Alkoxycarbenoids [YMCH(OR)X] 62 1.4.1 Zinc Carbenoids 62 1.4.2 Lithium Carbenoids 63 1.5 Carboalkoxy-Carbenoids [YMCR (CO 2 R )X] 64 1.5.1 Zinc Carbenoids 64 1.5.2 Mercury Carbenoids 66 1.5.3 Copper Carbenoids 66 1.5.4 Indium Carbenoids 70 1.6 Summary and Conclusions 72 Chapter 2. Results and Discussion 76 2.1 An Insight into The Generation of Organozinc Carbenoids from Carbonyl Compounds 77 2.1.1 The Clemmensen Reduction of Carbonyl Compounds 77 2.1.2 The Controlled Generation of Organozinc Carbenoids from Carbonyl Compounds 84 2.1.2.1 The Generation of Organozinc Carbenoids from Arylaldebydes with Zinc and Boron Trifluoride Dietbyletberate 84 2.1.2.2 The Generation of Organozinc Carbenoids from Carbonyl Compounds using Zinc and Cblorotrimetbylsilane 85 2.1.2.3 Dicarbonyl Coupling Reactions of Organozinc Carbenoids Generated from Carbonyl Compounds using Zinc and a Silicon Electropbile 87 2.1.2.4 Cyclopropanation with Organozinc Carbenoids Generated from Carbonyl Compounds using Zinc and a Silicon Electropbile 93 Contents 2.1.2.5 Cyclopropanation with Organozinc Carbenoids Generated from Acetals and Ketals 97 2.1.2.6 Alkoxy- and Aryl-oxycyclopropanation with Organozinc Carbenoids Generated from Orthoformates 98 2.2 Deoxygenation of Ketonesvia Formation of Organozinc Carbenoids 100 2.2.1Pyrolysis of Tosylhydrazone Salts 100 2.2.2 The Generation of Organozinc Carbenoids from Carbonyl Compounds using Zinc and Cblorotrimetbylsilane 106 2.2.3 The Generation of Organozinc Carbenoids from Carbonyl Compounds using Zinc and Cblorotrimetbylsilane in the Presence of an Additional Proton Source 108 2.2.4 The Generation of Organozinc Carbenoids from Carbonyl Compounds using Zinc and lodotrimetbylsilane 112 2.3 Electrochemical Generation of Organozinc Carbenoids 115 2.3.1 Basic Electrochemistry 115 2.3.1.1 Electrochemical Cell and Reaction Conditions 116 2.3.1.2 Electrochemical Activation of Zinc 116 2.3.2 Electrochemical Cyclopropanation of Alkenes 117 2.3.3 Attempted Generation of Organozinc Carbenoids from Carbonyl Compounds using Electrolysis 120 2.3.3.1 Dicarbonyl Coupling Reactions and Intermolecular Cyclopropanation 120 2.3.3.2 Deoxygenation Reactions 122 2.4 The Cyclopropanation of Electron Rich Dienes 123 2.4.1 Regioselectivity and Stereoselectivity of Organorbodium and Organozinc Carbenoids 124 2.4.2 Cyclopropanation of Electron Rich Dienes using Organozinc Carbenoids 125 2.4.3 Trapping of Organozinc Carbenoids using (Z)-l-Acetoxy- 1,3-butadiene 266 126 2.4.4 Trapping of Organozinc Carbenoids using 2-(l- Metbyletbenyl)- 1 -cyclobexen-1 -ol Acetate 294 134 Contents 2.5 The Generation and Reactivity of Organometallic Carbenoids from Geminal Dihalo and Novel Haloalkoxy Compounds 137 2.5.1 A Comparison of Organocopper and Organozinc Carbenoids in Carboalkoxycyclopropanations 138 2.5.2 The Generation of a Novel Geminal Alkoxy-Carboalkoxy Organocopper Carbenoid and Reactivity in Cyclopropanation 144 2.5.3 Attempted Generation of Organozinc Carbenoids from Novel Geminal Dihalo Intermediates 153 2.6 Studies on Aminocyclopropanation 157 2.6.1 Formation of Halo Iminium Salts 160 2.6.2 Attempted Generation of Organometallic Carbenoids from Halo Iminium Salts 163 2.6.3 Iminium and Oxonium Salts 168 Chapter 3. Conclusions and Perspectives 169 Chapter 4. Experimental 176 4.1 General Experimental 177 4.2 Experimental Procedures 180 Chapter 5. References 245 Acknowledgements ACKNOWLEDGEMENTS I am especially indebted to Professor Willie Motherwell for all his valuable guidance, enthusiasm, and inspiration over the last 4 years. I am also grateful to my industrial supervisor at Syngenta Agrochemicals, Dr. Adam Russell, for all his encouragement, support and advice. Special thanks goes out to all the technical staff at UCL especially Jorge Gonzales and Dr. Abil Aliev for NMR and John Hill for mass spectra. Thanks to both Syngenta Agrochemicals and the EPSRC for funding. The fast and careful work of my proof readers, Beatrice, Camilla, Oliver and Dr. Adam Russell, is also greatly appreciated. Over the duration of my PhD, it has been intriguing to work with so many talented chemists, past and present in the Motherwell group, from so many different countries. First and foremost, I thank Ray for helping me to settle in my first year. I also thank Rosa and Lynda who have always had the time to answer my questions and I will still probably believe everything you say to me. Thanks to Camilla who has been a great and understanding benchmate always full of advice and also Catherine for the friendly discussions on Northerners and Southerners. Thanks also to Beatrice, Oliver, Matt, Christoph, Yuan, Julian and all the others to numerous to mention for making the lab such a pleasant and friendly place to work. A special mention should be made to Robyn for keeping the things in the lab in order and also for the useful practical tips. I also thank all the scientists at Syngenta Agrochemicals for being friendly and making my short industrial experience such an enjoyable one. A special thanks to Dave for organising the cricket in the summer evenings. Outside the lab, I thank Jorge, Romano, Pilar, Maria, Ishfaq and Javed for their special friendship and light relief away from the lab. I would also like to thank my family in London; Rizwan, Shazia and aunty for always being there for me and cooking some wonderful dishes. I am also sincere to all my other members of my family especially Usman, Nadir, Fahrat, Nadeem and my grandmother, who have always been supportive and encouraging over the years.
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