Development of Novel Asymmetric Reactions Based on Acid-base Catalysis of Late Transition Metal Complexes

Abstract

Acid-base catalysis of chiral transition metal complexes having hard anionic ligands such as hydroxo and acetate ligands is described. The Pd, Pt, Cu, and Ni complexes can effectively abstract the α-proton of methylene and methine compounds under non-basic conditions to give chiral enolates. In the case of 1,3-dicarbonyl compounds, the Pd complexes produced such enolates even under acidic conditions, and their cooperative action with protic acid to activate the various electrophiles including enones, imines, and acetals allows unique C-C bond-forming reactions to proceed with excellent enantioselectivity. Additionally, asymmetric protonation in aza-Michael reaction using the Pd hydroxo complex in combination with amine salt is described. For efficient activation of less acidic α-ketoesters, we developed a novel chiral nickel acetate complex, which is particularly effective to promote the asymmetric conjugate addition to nitroolefins. To confirm the utility of the reaction, its application to the asymmetric synthesis of MFPA was successfully demonstrated. Finally, the proposed reaction mechanisms of these reactions are briefly discussed.