Long-Chained Acidic Ionic Liquids-Catalyzed Cyclization of 2-Substituted Aminoaromatics with β-Diketones: A Metal-Free Strategy to Construct Benzoazoles

With long-chained acidic ionic liquids as catalysts, a metal-free, efficient, and universal strategy was developed to synthesize a series of benzoazole compounds through intermolecular cyclization of 2-aminophenols/thiophenols/anilines with β-diketones. Compared with traditional ionic liquids, the long-chained ionic liquids with certain surfactivity exhibited better catalytic activities perhaps for micellar action and could be reused at least six times. A mechanism that involves condensation, nucleophilic addition, and C–C bond cleavage was proposed, and the imine compound was recognized as an important intermediate in the reaction.