Synthesis of benzo[b]thiophenes by electrophilic cyclization

2,3-Disubstituted benzo[b]thiophenes are readily prepared in excellent yields under very mild reaction conditions by the Pd/Cu-catalyzed cross-coupling of commercially available o-iodothioanisole and terminal alkynes, followed by electrophilic cyclization by I2, Br2, NBS, p-O2NC6H4SCl or PhSeCl.