p-Toluenesulfonic acid-mediated cyclization of o-(1-alkynyl)anisoles or thioanisoles: synthesis of 2-arylsubstituted benzofurans and benzothiophenes

A variety of 2-arylbenzo[b]furans are readily prepared in good to excellent yields from the cyclization of o-(1-alkynyl)anisole derivatives under mild reaction conditions using an alcoholic media, p-toluenesulfonic acid under microwave irradiation. Starting from the corresponding o-(1-alkynyl)thioanisole derivatives, this friendly and environmentally free-metal procedure has been successfully extended to the synthesis of benzo[b]thiophenes. Relative to the electronic nature of the substituents, the selectivity of the cyclization reaction from differently o,o′-substituted diarylalkynes is also discussed.