Site-Selective C(sp3)-H Bromination via Radical Relay.

A cobalt-catalyzed site-selective C(sp3)-H bromination via radical relay is reported. The mild and practical protocol uses NBS as the brominating reagent with only 1 mol % CoBr2 as the catalyst and achieves excellent benzylic selectivity (>20:1) over aliphatic C-H bonds, overcoming limitations of conventional bromination methods. It also features a broad substrate scope, good functional group tolerance, and scalability and enables late-stage bromination of complex bioactive natural products and pharmaceutical molecules.