Double C‐H bond functionalization for the annulative π‐extension of 1‐arylimidazoles: A palladium‐catalyzed one pot access to imidazophenanthridines

The Pd‐catalyzed annulative π‐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.