Rhodium-Catalyzed Synthesis of 2‑Methylindoles via C–N Bond Cleavage of <i>N</i>‑Allylbenzimidazole

A rhodium-catalyzed oxidative C–H/N–H dehydrogenative [3 + 2] annulation strategy has been reported between anilines and N-allylbenzimidazole for the synthesis of 2-methylindole scaffolds. An N-allylbenzimidazole has been used as a 2C synthon for the synthesis of indole, and more importantly, this transformation involves the cleavage of the thermodynamically stable C–N bond of allylamine. Detailed mechanistic studies have been performed and a key intermediate was detected in HRMS. This transformation proceeds through a cascade of C­(sp2)–H allylation followed by intramolecular cyclization.