Copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters with chiral phenol-carbene ligands.

A chiral phenol-NHC ligand enabled the copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters. The phenol moiety of the chiral NHC ligand played a critical role in producing the enantiomerically enriched products. The catalyst worked well for various ()-isomer substrates. Opposite enantiomers were obtained from ()- and ()-isomers, with a higher enantiomeric excess from the ()-isomer.