Zero-Valent Copper Catalysis Enables Regio- and Stereoselective Difunctionalization of Alkynes.

The development of a metallic copper-based catalyst system remains a significant challenge. Herein, we report the synthesis of highly stable, active, and reusable Cu catalyst for the carboboration of alkynes using carbon electrophiles and bis(pinacolato)diboron (Bpin) as chemical feedstocks to afford di- and trisubstituted vinylboronate esters in a regio- and stereoselective manner with appreciable turnover number (TON) of up to 2535 under mild reaction conditions. This three-component coupling reaction works well with a variety of substituted electrophiles and alkynes with broad functional group tolerance. In addition, a wide range of terminal and challenging internal alkynes were efficiently converted into hydroborated products in up to >99 % yield with excellent regioselectivity in the absence of carbon electrophiles. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy (XANES) analysis confirm that the oxidation state of the copper in the catalyst is zero. The broad range of organic transformations, effectiveness, and recyclability of this Cu catalyst are the major achievements that provide an environmentally friendly route for the efficient production of tri- and tetrasubstituted olefins, key intermediates in organic synthesis. The gram-scale reaction and synthetic transformations further highlights the usefulness of these methods.