Excess Phosphine Ligand Plays a Critical Role in the Asymmetric Copper(I) Iodide-Catalyzed Conjugate Addition of Grignard Reagents to α,β-Unsaturated Esters

The role of excess ligand in the asymmetric 1,4-conjugate addition (ACA) of Grignard reagents to alpha,beta-unsaturated esters compounds catalyzed by copper(I) iodide-2,2'-bis(di-p-tolylphosphino)-1,1'-binaphthyl (CuI-Tol-BINAP) is explored herein. In addition, this methodology allows asymmetric induction to be carried out using a nonchiral phosphine copper complex with excess of a chiral phosphine ligand.