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

Abstract

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^N^P ligand N(2) ,N(6) -bis(di-isopropylphosphino)pyridine-2,6-diamine revealed the highest catalytic activity for both reactions.

Enhanced Catalytic Properties of Molybdenum Promoted Mesoporous Cobalt Oxide: Structure‐Surface‐Dependent Activity for Selective Synthesis of 2‐Substituted Benzimidazoles

“…This method is preferred in terms of applications as a wide range of 2‐substituted benzimidazole derivatives could be obtained due to the availability of a high variety of aldehydes . However, these reactions require either stoichiometric amounts of hydrogen acceptors or strong bases in order to achieve efficient and selective benzimidazole yields, which has been an issue of high interest …”

A new class of PN3-pincer ligands for metal–ligand cooperative catalysis

“…More detailed discussion will be provided in Section 4. Acceptorless dehydrogenative alkylations have also been developed for the synthesis of benzimidazoles and quinoxalines with [95] (Scheme 35). Water and two equivalents of hydrogen are liberated during the course of the reactions.…”

Iridium catalyzed acceptor-less dehydrogenative coupling of alcohols and 4-hydroxy-6-methyl-2-pyrone under microwave conditions

“…5,6 Benzimidazoles and quinoxalines were also synthesized from aromatic diamines and alcohols via an iridium catalyzed acceptor-less dehydrogenative alkylation. 7 Milstein et al have…”