Bidentate NHC-Based Chiral Ligands for Efficient Cu-Catalyzed Enantioselective Allylic Alkylations: Structure and Activity of an Air-Stable Chiral Cu Complex

Abstract

Cu-catalyzed addition of alkylzinc reagents to a range of allylic phosphates is promoted efficiently and with high enantioselectivity to afford tertiary as well as quaternary carbon centers (up to 98% ee). Reactions proceed to completion with 0.5−5 mol % catalyst loading and are best promoted by commercially available CuCl₂·2H₂O. The X-ray structure of the chiral NHC−Ag(I) complex used in the study as well as that of a catalytically active NHC−Cu(II) complex are also reported; both complexes are air-stable and are formed in ≥95% isolated yield. The isolated Cu complex, which can be handled in air, is catalytically active. The present report provides the first precedent for efficient Cu-catalyzed allylic alkylations with chiral NHC ligands.