Sequential radical addition/cyclization/β-elimination reactions. 3-exo- and 5-exo-cycloaddition reactions of 5-phenylthio-3-pentenyl and 5-phenylthio-3-pentynyl radicals

Sequential radical addition/5-exo-cyclization/β-elimination reactions, accomplished by thermally or photolytically induced decompositions of O-acyl derivatives of N-hydroxypyridine-2-thione or other thiohydroxamic esters of 6-phenylthio-4-hexenoic acid 11 in the presence of an excess of radicophilic olefins, afforded the 2-vinylcyclopentane derivatives 13 in 50-90% yields, while decompositions of thiohydroxami esters or 6-phenylthio-4-hexynoic acids 24, under the same experimental conditions and in the presence of electron deficient olefins, afforded the corresponding 2-vinylidenecyclopentane (2-exo-allenic cyclopentane) derivatives 2 (61-72%). However, when decompositions of thiohydroxamic esters 39 were carried out in boiling toluene solution without radicophilic olefins, 3-exo-cyclization took place and the corresponding 2-vinylcyclopropane derivatives 40 were obtained in 43-60% yields. © 1992