Rhodium-Catalyzed Synthesis of 2-Methylindoles via C-N Bond Cleavage of N -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(sp 2 )-H allylation followed by intramolecular cyclization.