Dual role of Rh(III) catalyst enables regioselective halogenation of (electron-rich) heterocycles.

The Rh(III)-catalyzed selective bromination and iodination of electron-rich heterocycles is reported. Kinetic investigations show that Rh plays a dual role in the bromination, catalyzing the directed halogenation and preventing the inherent halogenation of these substrates. As a result, this method gives highly selective access to valuable halogenated heterocycles with regiochemistry complementary to those obtained using uncatalyzed approaches, which rely on the inherent reactivity of these classes of substrates. Furans, thiophenes, benzothiophenes, pyrazoles, quinolones, and chromones can be applied.