An Efficient Nucleophilic Carbene Catalyst for the Asymmetric Benzoin Condensation

Abstract

The chiral bicyclic triazolium salt 1 is currently the most efficient precatalyst for the asymmetric benzoin condensation. The substituted acyloins 3 are obtained in moderate to good yields and with very good enantiomeric excesses from the corresponding aldehydes 2. The high asymmetric induction is presumably based on the conformational rigidity of the bicyclic nucleophilic carbene catalyst and on the steric hindrance of the tert-butyl group in the Breslow intermediate.