Radical Sequential Processes Promoted by 1,5-Radical Translocation Reaction:  Formation and [3 + 2] Anulation of Alkenesulfanyl Radicals

Radical addition of 2-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 5-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.