Development of catalytic asymmetric reactions via chiral palladium enolates.

This article describes the generation of chiral palladium enolates and their application to several kinds of catalytic asymmetric reactions. Two methods to generate chiral enolates were developed using novel cationic palladium complexes 1 and 2. In these processes, water or a hydroxo ligand on palladium metal plays an important role as a nucleophile to promote the transmetallation or as a Brønsted base to abstract an acidic alpha-proton of the carbonyl group. These enolates showed sufficient reactivity with various electrophiles. Using a chiral Pd enolate as a key intermediate, highly enantioselective reactions such as catalytic aldol reactions, Mannich-type reactions, Michael reactions, and fluorination reactions were developed. The unique structures of the palladium enolate complexes were elucidated and reaction mechanisms are proposed.