Copper-Catalyzed Regioselective Formation of Tri- and Tetrasubstituted Vinylboronates in Air

The first in air copper-catalyzed method for the selective synthesis of tri- and tetrasubstituted vinylboronate derivatives is presented. Three different variants of the borylation of internal alkynes (alpha-hydroboration, beta-hydroboration, and carboboration) are described using a single catalyst: [Cu(Cl)(IMes)] (IMes = N,N'-bis-[2,4,6-(trimethyl)phenyl]-imidazol-2-ylidene) without taking any precaution to avoid the presence of air. Bis(pinacolato)diboron was used to afford beta-hydroborated products in the presence of methanol. Adding instead another electrophile allowed the formation of tetrasubstituted vinylboronate species. Finally, the alpha-products were obtained using pinacolborane as the boron source. All compounds were obtained in high yield with excellent regioselectivity at low catalyst loading (0.04-2, mol %). The protocol constitutes a very convenient route to access these highly valuable molecules.