Amorphous Fe_0.8Mn_0.2O_<i>x</i>-Catalyzed Four-Step Tandem Synthesis of Benzazoles from Alcohols and o-Substituted Anilines without Solvent

Benzazoles, as crucial intermediates, can be synthesized via a superior four-step tandem catalytic process from benzyl alcohols and o-substituted anilines. However, the reported catalysis system needs complex catalysts, toxoneic solvents, and additives; meanwhile, the efficient synthesis of benzimidazoles, benzoxazoles, and benzothiazoles using a single catalyst represents a substantial challenge in the field of synthetic chemistry. Herein, we constructed an amorphous Fe0.8Mn0.2Ox-300 catalyst by a simple coprecipitation method. Fe0.8Mn0.2Ox-300 can efficiently catalyze the four-step tandem synthesis of 2-arylbenzimidazole, 2-arylbenzoxazole, and 2-arylbenzothiazole from benzyl alcohol, o-phenylenediamine, 2-aminophenol, and 2-aminothiophenol, respectively, using O2 without solvent and additives. Comprehensive characterization revealed that Fe0.8Mn0.2Ox-300 possesses more oxygen vacancies and stronger oxygen capture capability, promoting the oxidation of alcohol and 2-aryl-2,3-dihydro-1H-benzimidazole. Due to its high density of acidic sites, Fe0.8Mn0.2Ox-300 effectively boosts the condensation and cyclization of aldehydes and amines while simultaneously inhibiting the formation of diamines, thereby enhancing the overall selectivity. Our work presents an alternative green approach for the industrial synthesis of benzazoles.