Synthesis of Benzo[b]thiophenes via Electrophilic Sulfur Mediated Cyclization of Alkynylthioanisoles

A stable dimethyl­(thiodimethyl)­sulfonium tetrafluoroborate salt was employed for the electrophilic cyclization reaction of o-alkynyl thioanisoles for the synthesis of 2,3-disubstituted benzo­[b]­thiophenes. The reaction described herein works well with various substituted alkynes in excellent yields, and a valuable thiomethyl group was introduced with ease. The reaction utilizes moderate reaction conditions and ambient temperature while tolerating various functionalities. To elucidate the mechanism, electrophilic addition reactions using the dimethyl­(thiodimethyl)­sulfonium tetrafluoroborate salt with diphenylacetylene was demonstrated.