FREE-RADICAL ADDITION OF ALKANETHIOLS TO ALKYNES - REARRANGEMENTS OF THE INTERMEDIATE BETA-THIOVINYL RADICALS

A variety of 2-mercapto-substituted vinyl radicals have been produced through the free-radical reaction of alkanethiols (including phenethyl, allyl, and benzyl mercaptans) with monosubstituted acetylenes in benzene at 90 degrees C. The 8-(benzylthio)vinyl radicals 6 readily rearranged to (vinylthio)methyl radicals 7 via a novel 1,4-migration of the phenyl group from thiomethyl to vinyl carbon; 2- (phenethylthio)vinyl radicals 12 underwent internal 1,5-hydrogen transfer to form beta-thio-substituted benzyl radicals 13 which in turn suffered fast beta-elimination of vinylthio radicals 18; and 2-(allylthio)vinyl radical 20 underwent kinetically preferred 5-exo cyclization to give the primary radical 26 which could easily rearrange to the more stable ring-expanded radical 25.