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Abstract:
This thesis describes the development of a new organocatalytic asymmetric epoxidation of cyclic and acyclic α,β-unsaturated ketones employing chiral primary amine salts as catalysts and hydrogen peroxide as inexpensive and environmentally benign oxidant. During the course of our work and stemming from serendipitous observations, we also developed an unprecedented and powerful catalytic asymmetric hydroperoxidation of α,β-enones providing access to optically active five-membered cyclic peroxyhemiketals (including representatives with a bicyclic peroxidic skeleton), in a single operation. The synthetic value and versatility of the products obtained was further illustrated by their expeditious conversion to highly enantioenriched acyclic as well as cyclic aldol products, the latter hitherto inaccessible by other synthetic means. Moreover, peroxyhemiketals serve as precursors to optically active 1,2-dioxolanes of potential biological relevance. The epoxidation method described herein further constitutes an interesting conceptual crossover between the well-established organocatalytic activation modes known as iminium ion and enamine catalysis, and the underlying mechanistic rationale is presented and discussed.
