Phase-transfer catalysed asymmetric epoxidation of enones using N-anthracenylmethyl-substituted Cinchona alkaloids

Abstract

A study into the enantioselective epoxidation of α,β-unsaturated ketones utilising Cinchona alkaloid-derived quaternary ammonium phase-transfer catalysts bearing an N-anthracenylmethyl function is presented. It has been found that the O-benzyl derivatives of these catalysts in conjunction with sodium hypochlorite give high enantio- and diastereoselectivities in the epoxidation of a range of substrates R1CH=CHCOR2, where R1=alkyl or aryl and R2=aryl. In the cases where R2=alkyl high enantioselectivity has also been observed, however the rate of reaction is substantially reduced. Application of this process to the enantioselective synthesis of a range of trans-α, β-epoxy ketones (e.e. 71–90%) is presented.