Comparison of chiral thiazolium and triazolium salts as asymmetric catalysts for the benzoin condensation

Abstract

Chiral bicyclic 1,2,4-triazolium salts having a defined face of the heterocyclic ring hindered have been synthesised and they catalyse the benzoin condensation in good yield; the enantiomeric excesses obtained (up to 80%) are much better than with closely related thiazolium salts and the opposite enantiomer of benzoin predominates.