Palladium-Catalyzed <i>trans</i>- and <i>cis</i>-Carboboration of Alkynes Tethered to Chloroborane with Organozirconium Reagents: Ligand-Dependent Complementary Stereoselectivity

Cyclizative carboboration of carbon−carbon triple bonds has been achieved with a wide range of organozirconium reagents, including alkenyl, aryl, and alkylzirconium, with chloroboranes tethered to alkynes in the presence of palladium catalysts. The carboboration takes two distinctive stereochemical courses depending upon the phosphine ligands used: PMe3 induces highly selective cis-carboboration, while bulkier phosphines such as PtBu3, PCy3, and PAr3 induce trans-carboboration selectively.