Synthesis of Benzoxazoles by Metal-Free Oxidative Cyclization of Catechols with Amines

Benzoxazoles are crucial in pharmaceuticals, agrochemicals, and functional materials. Their simple, economical, green, and efficient synthesis has attracted long-standing interest in synthetic chemistry. Herein, we present an extremely simple strategy for constructing benzoxazoles via the direct oxidative cyclization of readily available catechols and primary amines, using DDQ/EA and O-2/water oxidative systems, respectively. The DDQ/EA system demonstrates distinct advantages in substrate and functional group compatibility. In contrast, the O-2/water system, which is milder, greener, and more economical, excels in synthesizing C-2 alkyl-substituted benzoxazoles. Overall, these two systems provide complementary advantages and are both well-suited for gram-scale synthesis. Given its high simplicity and practicality, this strategy could serve as a promising alternative in benzoxazole synthesis.