Visible-light-induced C(sp 3 )-H bromination of 4-methylthiophene derivatives with HBr/H 2 O 2 .

A convenient method to synthesize ethyl 4-(bromomethyl)thiophene-3-carboxylate derivatives has been developed via a visible-light-induced radical process in good yields and with wide functional group tolerance under air conditions and at ambient temperature. The present protocol has the advantages of a high atom economy, easy purification, and environmental friendliness as it employs HBr as the bromine source and the cheap and low-toxic H 2 O 2 as the oxidant. The synthetic utility of this method is demonstrated by a gram scale reaction and its application in the innovative synthesis of the clinical drug relugolix.