Access to Stereodefined (E)-2-Silylallylboronates via Regioselective Chloroboration of Allenylsilanes.

A catalyst-free method for the highly regioselective chloroboration of allenylsilanes is described. In the presence of BCl3 and 2,6-lutidine, chloroboration of allenylsilanes proceeds smoothly without any catalyst, and the product could be treated with pinacol to afford the corresponding pinacol borates in one-pot reaction. This reaction provides a direct approach to construct valuable 2-silylallylboronate frameworks with operational simplicity and high atom-economy.