Radical sequential processes promoted by 1,5-radical translocation reaction: Formation and [3+2] anulation of alkenesulfanyl radicals

Radical addition of a-substituted ethanethiols 1-5 to alkyl-, dialkyl-, and phenylacetylenes affords the corresponding beta-sulfanylalkenyl radicals, which can undergo 1,5-radical translocation (RT reaction) in competition with intermolecular hydrogen abstraction (HA reaction). The RT reaction is the first step of a sequential radical process leading to alkenesulfanyl radicals through an ''intermolecular sulfanyl radical transaddition'' from an alkene to an alkyne molecule. Alkenesulfanyl radicals can undergo a regioselective [3 + 2] anulation reaction with a CC triple bond, eventually leading to thiophene products through B-endo cyclization of vinyl radicals onto CC double bond. The effect of the nature of ethanethiol and alkyne substituents on the RT/HA ratio has been investigated, and results will be discussed.