Rh(III)-Catalyzed [4 + 2] Spiroannulation of 2-Phenylbenzimidazoles with Isomerizable 3-Methylmaleimides: Synthesis of Spiro-Fused Benzimidazoisoquinoline Succinimides.

A Rh(III)-catalyzed exclusive [4 + 2] cascade cyclization of 2-phenylbenzimidazoles with 3-methylmaleimides for the synthesis of spiro-fused benzimidazoisoquinoline succinimides via C-H activation is reported. The detailed mechanistic study revealed that the reaction proceeds through N-directed C-H activation of 2-phenylbenzimidazole. Subsequent migratory insertion of the rhodium-mediated formation of isomeric maleimide into the Rh-C bond and reductive elimination affords the polycyclic spiro-fused benzimidazoisoquinoline succinimide.