An N-heterocyclic carbene copper chloride (NHC-CuCl) complex has been prepared and used to catalyze the conjugate reduction of alpha,beta-unsaturated carbonyl compounds. The combination of catalytic amounts of 2 and NaOt-Bu with poly(methylhydrosiloxane) (PMHS) as the stoichiometric reductant generates an active catalyst for the 1,4-reduction of tri- and tetrasubstituted alpha,beta-unsaturated esters and cyclic enones. The active catalytic species can also be generated in situ from 1,3-bis(2,6-di-isopropylphenyl)-imidazolium chloride (1) CuCl2.2H(2)O in the presence of NaOt-Bu and PMHS.
“Conjugate Reduction of α,β-Unsaturated Carbonyl Compounds Catalyzed by a Copper Carbene Complex”, Org. Lett., 2003, 5(14), 2417-2420.