Metal-free direct annulation of 2-aminophenols and 2-aminothiophenols with unactivated amides through transamidation: Access to polysubstituted benzoxazole and benzothiazole derivatives

Abstract

We herein report a simple yet novel oxidant, metal and solvent-free green protocol for synthesising differently 2-substituted 1,3-benzoxazoles and benzothiazoles from 2-aminophenol hydrochloride salt unactivated amide as in situ carbon source. Further, the hydrogen ion of hydrochloride played a crucial role in amide activation followed nucleophilic attack that through eliminations of amine as a side product, and de-hydrolysis step leads to final annulation. This versatile strategy is applicable to a wide variety of differently substituted o-aminophenols, unactivated aliphatic and aromatic amides, yielding the corresponding product in good to excellent yields in a single step.