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

Article abstract of DOI:10.1246/bcsj.73.999

A mixture of CuCN and N-benzylbenzenesulfonamide catalyzes the 1,4- addition of dialkylzincs or diarylzincs (Cu: Zn = 1: 200 to 1: 10000) to α,β-unsaturated ketones to give, after aqueous workup, the corresponding β-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.