Catalytic Enantioselective Protonation of Lithium Ester Enolates Generated by Conjugate Addition of Arylthiolate to Enoates.

A chiral ligand, a catalytic amount of lithium cation, and no chiral proton source: These are features of the present asymmetric addition-protonation of propenoates with 2-trimethylsilylbenzenethiol. The reaction is catalyzed by a combination of lithium 2-trimethylsilylbenzenethiolate and the chiral ligand 1. Desulfurization of the product affords 2-substituted propanoates with high ee values and without racemization. Furthermore, 1 can be recovered quantitatively for reuse.