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 fully regio‐ and stereo‐selective syn ‐β‐silylmagnesiation occurs affording, after trapping with a broad variety of electrophiles, a unique and selective access to polysubstituted silylated enamides, versatile building blocks for chemical synthesis. The silylmagnesiation can moreover be performed on other simple alkynes bearing a directing group, while in the absence of the copper catalyst, a full reversal of both the regio‐ and stereo‐selectivities can be achieved, a rare anti ‐α‐silylmagnesiation taking place.