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. [ABSTRACT FROM AUTHOR]