One-Pot Process to Carborano-Coumarin via Catalytic CascadeDehydrogenative Cross-Coupling

Ir-catalyzed cascade dehydrogenative CH/BH and BH/OH cross-coupling of carboranyl carboxylic acid with readily available benzoic acid has been achieved, leading to the facile synthesis of previously unavailable carborano-coumarin in a simple one-pot process. Two cage B-H, one aryl C-H and one O-H bonds are activated to construct efficiently new B-C and B-O bonds. The cascade cyclization can stop at the first B-H/C-H cross-coupling step by tuning the reaction conditions, resulting in a series of alpha-carboranyl benzoic acid and aryl carborane derivatives. Control experiments indicate that B-H/C-H dehydrocoupling proceeds preferentially over B-H/O-H dehydrocoupling, and both directing groups and oxidants are crucial for this reaction. An iridium(V) intermediate is proposed to be involved in the catalytic cycle.