Mann, S.E.; (2011) New reactions of cyclic oxygen, nitrogen and sulfur acetal derivatives. Doctoral thesis , UCL (University College London).

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Abstract

This thesis describes the development of new reactions of cyclic oxygen, nitrogen and sulfur acetal derivatives and their applications in a diverse range of synthetic organic and organometallic chemistry. Detailed herein are advances in three main areas of acetal chemistry, namely: studies towards a new methodology for the synthesis of medium ring heterocycles; the use of thioacetals as directing groups for the palladium-mediated oxidation of olefins; and multi-component reactions for the synthesis of drug-like heterocyclic compounds. A brief overview of the chemistry of cyclic acetal derivatives is given in the first chapter, followed by a chapter on each of the three areas investigated. Relevant introductory literature is reviewed at the beginning of each chapter. Firstly, the ring expansion chemistry of unsaturated cyclic oxygen, nitrogen and sulfur acetal derivatives was explored for the development of a new methodology for the synthesis of medium ring heterocycles. This methodology has thus far proved unsuccessful in the synthesis of medium rings, although several interesting and unusual transformations were observed, such as the unexpected formation of an intriguing bicyclic enaminium salt. The use of thioacetals as directing groups for the palladium-mediated oxidation of terminal olefins was also explored, leading to the evolution of a new methodology for the catalytic, regioselective formation of either vinyl or allylic acetates. Dithianes were shown to stabilise intermediates in the allylic oxidation pathway, allowing their structure elucidation and characterisation by low-temperature NMR spectroscopy and in one case X-ray crystallography. This enabled a detailed mechanistic study leading to the observation of two finely balanced, divergent reaction mechanisms. Finally, building upon previously unpublished results, a number of three and four-component reactions were investigated, giving drug-like α-aminoamides; this methodology was applied to the synthesis of some medium ring heterocycles.

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