One‐Pot Synthesis of Pyrrolo[3,4‐ a ]indolizine‐1,3‐diones through [3+2] Cycloaddition‐Oxidation Reaction Catalyzed by Cu II Salt and O 2 as the Oxidant

An efficient one‐pot synthesis of pyrrolo[3,4‐ a ]indolizine‐1,3‐diones has been developed from maleimides, pyridines, and acyl bromides through a [3+2] cyclization–oxidation reaction catalyzed by Cu II salt under O 2 atmosphere. The advantage of this method is the use of molecular oxygen as the oxidant, in the presence of a catalytic amount of hydrated copper(II) chloride, to accomplish the reaction with broad substrate scope and excellent yields.