Radical Addition Cascade Cyclization of 1,6-Enynes with DMSO To Access Methylsulfonylated and Carbonylated Benzofurans under Transition-Metal-Free Conditions.

A mild and direct addition/cyclization cascade to construct methylsulfonylated and carbonylated benzofurans was accomplished using oxygen-linked 1,6-enynes as the starting materials. The interaction of NH4I and DMSO promoted the generation of sulfur-containing radical and initiated the radical addition to the C═C double bond of 1,6-enyne cascade intramolecular 5- exo- dig cyclization. A wide range of oxygen-linked 1,6-enynes bearing various substituents were found to be suitable in this cascade process, providing benzofurans with dual functional groups in moderate to high yields. This method could also be utilized to synthesize benzothiophenes from sulfur-linked 1,6-enynes.