Double C-H bond functionalization for the annulative pi-extension of 1-arylimidazoles: A palladium-catalyzed one pot access to imidazo[1,5-f]phenanthridines

International audienceThe Pd-catalyzed annulative pi-extension reaction of 1-arylimidazoles for the one pot preparation of imidazo[1,5-f]phenanthridines was explored. The higher reactivity of imidazole C5-H bond compared to C2-H bond of imidazoles for Pd-catalyzed direct arylation in the presence of carboxylate bases allows the selective synthesis of imidazo[1,5-f]phenanthridines. The reaction proceeds via successive palladium-catalyzed direct intermolecular C5-arylation of the imidazole unit followed by an intramolecular direct arylation step. This synthetic pathway allowed us to describe the first synthesis of imidazo[1,5-f]phenanthridine. Moreover, by using the appropriate substrates, the introduction of desired functional groups at positions 5, 7, 10, and 11 of imidazo[1,5-f]phenanthridines is possible