Palladium-Catalyzed Direct Dialkenylation of Cage B-H Bonds in o-Carboranes through Cross-Coupling Reactions.

Palladium-catalyzed direct dialkenylation of cage B(4,5)-H bonds in o-carboranes has been achieved with the help of a carboxylic acid directing group, leading to the preparation of a series of 4,5-[trans-(ArCH=CH)]2-ocarboranes in high yields with excellent regioselectivity. The traceless directing group, eliminated during the course of the reaction, is responsible for controlling regioselectivity and dialkenylation. A possible catalytic cycle is proposed, involving a tandem sequence of Pd(II) -initiated cage B-H activation, alkene insertion, β-H elimination, reductive elimination, and decarboxylation.