Divergent Silylmagnesiation of Ynamides: an Efficient and Versatile Entry to Polysubstituted Enamides

A set of selective and divergent procedures for the silylmetallation of ynamides is reported. Upon simple reaction with a silyl-Grignard reagent in the presence of catalytic amounts of copper bromide, a beta-selective, syn-silylmagnesiation occurs affording a unique and selective access to polysubstituted silylated enamides. The silylmagnesiation can be utilized with other alkynes and in the absence of the copper catalyst, a full reversal of selectivity can be achieved, a rare alpha-selective, anti-silylmagnesiation taking place.