Asymmetric aldol reactions of achiral 2-phenylsulfanyl aldehydes with small- and medium-sized carbocyclic rings: the synthesis of homochiral spirocyclic lactones, pyrrolidines and tetrahydrofurans

Abstract

Chiral boron enolates based on the 1,3-oxazolidin-2-one auxiliary react with achiral 1-phenyl-sulfanylcycloalkanecarbaldehydes in anti- and syn-selective aldol processes to give the corresponding aldol products with moderate to excellent levels of diastereo- and enantio-control. Stereospecific cyclisation via an asymmetric episulfonium (thiiranium) ion leads to optically pure spirocyclic compounds in high chemical yields.