Organocatalysed Asymmetric Oxidation Reactions

Abstract

This review highlights the progress of highly enantioselective ­organocatalytic systems for asymmetric oxidation. For example, since the first reported enantioselective dioxirane catalysts developed independently by Curci and Marples, several systems have been developed which give greater than 90% ee for ­epoxidation. Dioxiranes have also been used for a range of other oxidation reactions including C–H oxidation. Oxaziridines have been widely used for the enantioselective oxidation of sulfides, alkenes and they have recently been reported, for the first time, to catalyse the epoxidation and C–H hydroxylation of a range of substrates. Oxaziridinium salts, the quaternised analogues of oxaziridines are prepared in situ from the corresponding iminium ions and ees of up to 97% have been achieved. The epoxidation of α,β-unsaturated ketones has been successfully achieved using asymmetric phase transfer catalysis and in situ amine/enamine catalysis.