Catalytic Cascade Dehydrogenative Cross-Coupling of BH/CH and BH/NH: One-Pot Process to Carborano-Isoquinolinone

A proof-of-principle study of cascade dehydrogenative cross-coupling of carboranyl carboxylic acid with readily available benzamide has been achieved, resulting in the facile synthesis of previously inaccessible carborano-isoquinolinone derivatives in a simple one-pot process, in which two cage B–H, one aryl C–H, and one N–H bond were sequentially activated to construct efficiently new B–C and B–N bonds, respectively. Under suitable reaction conditions, such cascade cyclization can be stopped at the first B–H/C–H cross-coupling step to give a series of α-carboranyl benzamides, suggesting the preferential occurrence of B–C cross-coupling over that of B–N. The carboxylic acid directing group plays a key role in the B–C cross-coupling step, which is then removed through in situ decarboxylation. The CV results combined with control experiments indicate that high-valent Ir­(V)-species may be involved in the reaction pathways, which is crucial for such cascade dehydrogenative cross-coupling reactions. The isolation and structural identification of a key intermediate, its controlled transformations, and deuterium labeling experiments support a new Ir-nitrene-mediated amination for B–H/N–H dehydrocoupling.