Heteroatom-Assisted Regio- and Stereoselective Hydrosilylation of Unsymmetric Internal Alkynes by Scandium Catalyst.

The catalytic hydrosilylation of alkynes with hydrosilanes is the most straightforward and atom-efficient method for the synthesis of silylalkenes. However, the hydrosilylation of unsymmetrical internal alkynes often encounters regio- and stereoselectivity challenges. Herein, we report the regio- and syn-stereoselective hydrosilylation of unsymmetrical internal alkynes bearing heteroatom functional groups with hydrosilanes by half-sandwich scandium catalyst. This protocol offers an atom-efficient route for the synthesis of a new family of heteroatom (O, S or N)-functionalized multisubstituted silylalkenes from a variety of internal homopropargyl thioethers, ethers and tertiary amines and hydrosilanes, featuring 100 % atom-efficiency, broad substrate scope, and excellent regio- and syn-stereoselectivity (>19 : 1 r.r. and >19 : 1 syn/anti). The mechanistic details have been elucidated by control experiments and isolation and examination of some key reaction intermediates. It was revealed that an interaction between the heteroatom (O, S or N) in the internal alkynes and the Sc center was critical for achieving the unprecedented high selectivity.