Rhodium catalyzed cascade cyclization featuring B–H and C–H activation: one-step construction of carborane-fused N-polyheterocycles

A one-pot strategy for efficient and facile synthesis of C,B-substituted carborane-fused N-polyheterocycles is reported. A rhodium catalyzed cascade cyclization of carboranyl N-arylimines with vinyl ketones enables the effective construction of three new B–C and C–C bonds in one reaction. Both carboranyl B–H and aryl C–H bonds are sequentially activated, leading to a series of previously unavailable C,B-substituted carborane-fused cyclopenta[b]quinoline derivatives, for potential applications in pharmaceuticals and materials, in a step-economical manner. The successful isolation and structural identification of a key intermediate provide solid evidence for the reaction mechanism, involving a tandem sequence of regioselective B–H activation, alkene insertion, nucleophilic cyclization, C–H activation, nucleophilic cyclization, dehydration and oxidative aromatization.