A Radical Cascade Cyclization To Prepare Dihydrothiophenes Induced by Thiyl Radicals as Sulfur Biradical Equivalents

Bicyclic dihydrothiophenes are readily
prepared by a radical cascade
cyclization reaction triggered by the addition of a thiyl radical
under thermal or photoirradiation conditions. The translocated radical
attacks the sulfur atom in the initial radical donor unit in an SHi manner. Sufficient stereoselectivity is achieved when a
large excess of disulfide is used for the reaction under photoirradiation
conditions. The reaction in the absence of solvents provides vinylsulfides
instead of dihydrothiophenes. Thus, the sulfur atom in the thiyl radical
serves as a sulfur biradical synthetic equivalent.