Highly functionalized heterogeneous dendrigraft catalysts with peripheral copper moieties for the facile synthesis of 2-substituted benzimidazoles and 2,2-disubstituted benzimidazoles

摘要

The synthesis of dendrigraft amidoamine polymers with glycerol initiated polyepichlorohydrin cores has been demonstrated on a Merrifield resin support to achieve heterogenosity for catalytic applications. In earlier studies of supported dendritic systems, no effort has been initiated to synthesize a dendritic polymer with high functionality at a low generation. The copper complexes of the Gn (n = 0, 1, 2) dendrigraft polymers were found to be excellent catalysts for the synthesis of benzimidazole derivatives via reactions between o-phenylenediamine and aldehydes. Aliphatic and cyclic ketones also showed excellent conjugation with o-phenylenediamine. A detailed study of the synthesis of 2-substituted benzimidazoles and 2,2-disubstituted benzimidazoles was performed with dendrigraft G2 copper catalyst. The reusability of the catalyst was examined for five consecutive steps, and no significant loss of catalytic activity was observed. The catalyst possessed the following green attributes: the final oxidation step was conducted using air, only a small amount of catalyst was needed to drive the reaction, and ethanol was used as the solvent under room temperature conditions.