Reversal of enantioselectivity of asymmetric conjugate addition: Carbene ligand- or copper precatalyst-based stereocontrol

Abstract

A new hydroxyamide-functionalized N-heterocyclic carbene (NHC) ligand was designed. Asymmetric reaction of cyclic enone with Et₂Zn catalyzed by Cu(OTf)₂ in the presence of the NHC precursor azolium took place to give the corresponding conjugate addition product. It was found that the reversal of enantioselectivity was achieved when the reaction was carried out by using Cu(acac)₂ combined with the same ligand precursor.