Visible-light-induced halocyclization of 2-alkynylthioanisoles with simple alkyl halides towards 3-halobenzo[b]thiophenes without an external photocatalyst.

A new strategy for the preparation of 3-halobenzo[b]thiophenes via a photo-driven halocyclization/demethylation of 2-alkynylthioanisoles with simple alkyl halides was developed. The reaction can proceed smoothly at room temperature under visible-light irradiation without any external photocatalyst, and the protocol has a range of advantages, including simplicity and mildness of the reaction conditions, good functional-group tolerance, and excellent yields of the products.