Enantioselective synthesis of heteroaromatic epoxyketones under phase-transfer catalysis using d-glucose- and d-mannose-based crown ethers

Abstract

Heteroaromatic epoxyketones have been synthesized in an asymmetric Darzens condensation of 2-chloroacetylfuran or 2- and 3-chloroacetylthiophene with aromatic aldehydes and in the enantioselective epoxidation of α,β-enones with an N-methylpyrrole unit, in both cases in the presence of d-glucose- 1 or d-mannose-based 2 crown ethers as phase transfer catalysts. The use of d-glucose-based 1 lariat ether as the catalyst gave the best results. The α,β-epoxyketones with a furan or a thiophene moiety were obtained in good enantioselectivities (up to 86% ee) as well as excellent diastereoselectivities (up to 98:2), but the epoxyketones with a pyrrole-ring were formed in the Darzens condensation in low yields and enantioselectivities. The epoxyketones with an N-methylpyrrole moiety isolated from the epoxidation of the corresponding α,β-enones were obtained in significant enantioselectivities (in ee values up to 81%) in the presence of catalyst 1 under mild reaction conditions.