Abstract: | 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‐(ArCHCH)]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 PdII‐initiated cage B H activation, alkene insertion, β‐H elimination, reductive elimination, and decarboxylation. |