Synthesis of phenanthridines via palladium-catalyzed picolinamide-directed sequential C-H functionalization

We report a new synthesis of phenanthridines based on palladium-catalyzed picolinamide-directed sequential C-H functionalization reactions starting from readily available benzylamine and aryl iodide precursors. Under the catalysis of Pd(OAc)₂, the ortho- C-H bond of benzylpicolinamides is first arylated with an aryl iodide. The resulting biaryl compound is then subjected to palladium- catalyzed picolinamide-directed intramolecular dehydrogenative C-H amination with PhI(OAc)₂ oxidant to form the corresponding cyclized dihydrophenanthridines. The benzylic position of these dihydrophenanthridines could be further oxidized with Cu(OAc)₂, removing the picolinamide group and providing phenathridine products. The cyclization and oxidation could be carried out in a single step and afford phenathridines in moderate to good yields.