Phosphine-Catalyzed <i>Anti</i>-Carboboration of Alkynoates with Alkyl‑, Alkenyl‑, and Arylboranes

We found that trialkylphosphine organocatalysts promoted unprecedented <i>anti</i>-carboboration of alkynoates with alkyl-, alkenyl-, or arylboranes to form β-boryl acrylates. The regioselectivity of the carboboration across the polar C–C triple bond exhibited inverse electronic demand, with the less electronegative B atom being delivered to the positively charged β carbon atom. The regioselectivity and the <i>anti</i> stereoselectivity were both complete and robust. In addition, the substrate scope was broad with excellent functional group compatibility