HIGHLY SELECTIVE THIOSELENATION OF OLEFINS USING DISULFIDE DISELENIDE MIXED SYSTEM

A highly selective thioselenation of olefins has been attained by using a disulfide-diselenide mixed system. Upon irradiation through Pyrex with a tungsten lamp in the absence of solvent, the thioselenation of olefins 1 with diphenyl disulfide (2) and diphenyl diselenide (3) takes place to provide 1-(phenylthio)-2-(phenylseleno)alkanes 4 as a sole product in good yields. In the cases of terminal olefins, the thioselenation proceeds regioselectively. The cyclic olefins like cyclopentene and cyclohexene also undergo thioselenation to give corresponding E isomers stereoselectively. The reaction of the conjugate diene with diphenyl disulfide and diphenyl diselenide produces the 1,4-thioselenation adduct in good yield. The excellent regioselectivity observed in the thioselenation of the terminal olefins is due to the higher reactivity of PhS., compared with PhSe., toward carbon-carbon double bonds and the higher capturing ability of (PhSe)2, compared with (PhS)2, toward carbon radicals.