HBr as a dual functional catalyst enabling aerobic CDC coupling of quinoxalin-2(1H)-ones with electron-rich heteroarenes

Abstract

Cross-dehydrogenative coupling (CDC) reactions offer high atom economy and simple synthetic routes, and are widely employed for the coupling of heterocyclic rings. Herein, we report a transition-metal-free HBr-catalyzed aerobic CDC reaction of quinoxalin-2(1H)-ones with different heterocycles at room temperature, which enables the efficient construction of biheteroarene scaffolds. The heteroarene substrate scope of this reaction includes furans, pyrroles, thiophenes, and indoles, affording the corresponding biheteroarene products in good to excellent yields. This method features mild and sustainable conditions, green oxidants, high atom economy, and broad functional group tolerance. Mechanistic studies reveal that HBr serves as a dual-functional reagent in this system, the proton serves as a Brønsted acid to activate quinoxalin-2(1H)-ones and bromide serves as an electron-transfer mediator in the aerobic oxidative aromatization.