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). T he RT reaction is the first step of a sequential radical process leadi ng to alkenesulfanyl radicals through an ''intermolecular sulfanyl rad ical transaddition'' from an alkene to an alkyne molecule. Alkenesulfa nyl radicals can undergo a regioselective [3 + 2] anulation reaction w ith 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 rati o has been investigated, and results will be discussed.