1,4-addition of diorganozincs to α,β-unsaturated ketones catalyzed by a copper(I)-sulfonamide combined system

A mixture of CuCN and N-benzylbenzenesulfonamide catalyzes the 1,4-addition of dialkylzincs or diarylzincs (Cu:Zn = 1 :200 to 1 : 10000) to alpha,beta-unsaturated ketones to give, after aqueous workup, the corresponding beta-substituted ketones in nearly quantitative yields. A range of cyclic enones having s-cis or s-trans geometries as well as conformationally flexible acyclic enones are usable as substrates. The ethyl group migrates more readily than the methyl and phenyl groups. CuOTf, CuO-t-C4H9, and mesitylcopper can be used in place of CuCN. The in situ-formed alkylzinc enolate, prior to aqueous workup, further undergoes an aldol reaction with aldehydes or Pd(0)-assisted coupling with allyl acetate, resulting in regio-controlled, vicinal carbacondensation products. A catalytic cycle is proposed on the basis of a kinetic study and a structural analysis of the zinc enolate product by NMR and molecular weight measurements.