Conjugate Reduction of α,β-Unsaturated Carbonyl Compounds Catalyzed by a Copper Carbene Complex

Abstract
An N-heterocyclic carbene copper chloride (NHC−CuCl) complex (2) has been prepared and used to catalyze the conjugate reduction of α,β-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 α,β-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) CuCl2·2H2O in the presence of NaOt-Bu and PMHS.