Nutley, Caroline Joy; (1995) The generation and reactivity of organozinc carbenoids. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis concerns an investigation into the generation and reactivity of organozinc carbenoids, from both a practical and mechanistic standpoint, using the reductive deoxygenation of carbonyl compounds with zinc and a silicon electrophile. The first introductory chapter is a review of organozinc carbenoids in synthesis. The second chapter opens with an overview of the development of the reductive deoxygenation of carbonyl compounds with zinc and a silicon electrophile since its inception in 1973. The factors influencing the generation of the zinc carbenoid are then investigated using a control reaction, and discussed. The results from a study to determine whether the carbenoid is homogeneous or heterogeneous are given, and the implications of the results considered. The influence of the electronic nature of the alkene on cyclopropanations is then examined using firstly a series of variously para-substituted alkenes, and then a series of electronically 'extreme' alkenes. In spite of the complexity of this heterogeneous system, a mechanistic rationale is presented to account for all the results. More preparative applications of the reactivity of the carbenoid are then presented. The first report of the cyclopropanation of cyclic enol ethers using the reaction system developed is made. The synthetic scope of a novel intermolecular C-H insertion reaction found in this system is also probed. The implications of preliminary results from a complex intramolecular system are discussed. Attempts to provide a mechanistic appraisal of the results using a specifically labelled system are then presented. Finally, attempts to carry out ylide-rearrangement reactions, and particularly a biomimetic [2,3]-sigmatropic rearrangement of an S-prenyl ylide, derived by trapping the carbenoid formed from prenal onto 3-methyl-1-thiophenyl-but-2-ene, are discussed. These results, and their implications, are drawn together in a concluding chapter, and full experimental details (together with complete spectral data for all compounds synthesised) are appended.

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