Synthesis of Phenanthridin-6(5H)-ones via Copper-Catalyzed Cyclization of 2-Phenylbenzamides

Synthesis of phenanthridin-6(5H)-ones was achieved via copper-catalyzed cyclization of 2-phenylbenzamides using air as the oxidant and KOt-Bu as the base. It was discovered that, besides Ph3P, other ligands such as 1,10-phenanthroline, TMEDA as well as L-proline could also be used as the ligand to effect the transformation.