The Synthesis of Benzimidazoles and Quinoxalines from Aromatic Diamines and Alcohols by Iridium-Catalyzed Acceptorless Dehydrogenative Alkylation

Benzimidazoles and quinoxalines are important N-heteroaromatics with many applications in pharmaceutical and chemical industry. Here, the synthesis of both classes of compounds starting from aromatic diamines and alcohols (benzimidazoles) or diols (quinoxalines) is reported. The reactions proceed through acceptorless dehydrogenative condensation steps. Water and two equivalents of hydrogen are liberated in the course of the reactions. An Ir complex stabilized by the tridentate P boolean AND N boolean AND P ligand N-2,N-6-bis(di-isopropylphosphino)pyridine-2,6-diamine revealed the highest catalytic activity for both reactions.