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

Abstract

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: PMe 3 induces highly selective cis -carboboration, while bulkier phosphines such as P t Bu 3, PCy 3, and PAr 3 induce trans -carboboration selectively.