DMTSF-mediated electrophilic cyclization for the synthesis of 3-thiomethyl-substituted benzo[b]furan derivatives.

Benzofuran is an important backbone for molecules that make up several pharmaceuticals, herbicides/pesticides, and organo-electronics. An environmentally benign dimethyl(methylthio)sulfonium tetrafluoroborate salt was used as an electrophile to induce cyclization of o-alkynyl anisoles to form 2,3-disubstituted benzofurans. The cyclization is performed at ambient reaction conditions, only takes 12 hours to get excellent yields, and shows a high tolerance for various substituted alkynes. Also, a sulfurmethyl group obtained after the cyclization reactions allows for a cascade cyclization, and an alkyne is used in the reaction to create a thieno[3,2-b]benzofuran core structure.