(CAAC)Copper Catalysis Enables Regioselective Three-Component Carboboration of Terminal Alkynes

Cyclic­(alkyl)­(amino)­carbene (CAAC) ligands are found to perturb regioselectivity of the copper-catalyzed carboboration of terminal alkynes, favoring the less commonly observed internal alkenylboron regiosomer through an α-selective borylcupration step. A variety of carbon electrophiles participate in the reaction, including allyl alcohol derivatives and alkyl halides. The method provides a straightforward and selective route to versatile trisubstituted alkenylboron compounds that are otherwise challenging to access.