Copper-Catalyzed Synthesis of 3-Aryl-9 H -imidazo[1,5- a ]indol-9-ones Using Oxygen as the Sole Oxidant.

A three-component strategy was developed for 3-phenyl-9 H -imidazo[1,5- a ]indol-9-one preparation from indole-2-carboxaldehydes, aromatic aldehydes, and ammonium acetate under copper catalysis conditions. In this process, a new five-membered ring was formed and the C3 position in the indole substrate was selectively oxidized into a ketone skeleton using oxygen as the sole oxidant and ammonium acetate as the nitrogen source. Furthermore, same products also could be achieved from indole-2-carboxaldehydes and benzyl amines under similar reaction conditions.