Ni(0)-Catalyzed Conjugate Addition of Me3SiCN to Ynones: α-Bromo-β-cyano Tetrasubstituted Enones

Conjugate addition of Me3SiCN to ynones is smoothly catalyzed by Ni(cod)2 to give the β-cyanosilyloxyallene quantitatively. Further reaction of the silyloxyallenes with NBS provides the tetrasubstituted α-bromo-β-cyano enones in high yields (up to 95%) with excellent Z-selectivity (E/Z = up to >1/99). X-ray crystallographic analysis showed a bent structure of the α-bromo-β-cyano enone due to a deconjugation of the π-bond and carbonyl group.