Chiral Pd aqua complex-catalyzed asymmetric C–C bond-forming reactions: a Brønsted acid–base cooperative system

Abstract

Chiral cationic Pd aqua complexes can function as acid–base catalysts, effectively activating active methylene and methine compounds to give chiral Pd enolates. It is noteworthy that such enolate formation occurs with concomitant formation of a strong protic acid. Although the reactivity of the Pd enolate itself is not sufficient for reactions with carbon-based electrophiles, its cooperative action with the protic acid to activate the electrophiles allows the desired C–C bond-forming reactions to proceed smoothly in a highly enantioselective manner. Based on this mechanistic feature, reactions with acetals have been developed; these are difficult to achieve using conventional basic enolate chemistry.