Brønsted Base-Mediated Regio- and Stereoselective trans-Silaboration of Propargylamides: Access to 1,2-Vinylborasilanes.

A facile method for the preparation of β-boryl-α-silyl aryl acrylamides using phenyllithium, dimethylphenylsilylpinacolborane, and propargylamides is reported. A key feature of this transition metal-free reaction is the Brønsted base deprotonation of aryl secondary propargylamide to produce a Lewis base that activates the B-Si bond, which is followed by a sequential intramolecular α-silylation-trans-β-borylation. The reaction proceeds in complete regio- and stereoselectivity. A wide variety of N- and aryl-substituted propargylamides afford trans-1,2-vinylborasilanes in high yield. The vicinal borasilane products undergo a variety of subsequent chemoselective transformations.