UNEXPECTED LEAVING ABILITY OF (PHENYLTELLURO)FORMATES IN THE PRESENCEOF INTERNAL NUCLEOPHILES - COMPLICATIONS DURING ALKYL AND OXYACYL RADICAL GENERATION IN THE PREPARATION OF SULFUR-CONTAINING AND SELENIUM-CONTAINING HETEROCYCLES

Irradiation of a benzene solution of 1-(benzylseleno)-3-undecyl (pheny ltelluro)formate (13) with a 250-W low-pressure mercury lamp leads to the formation of 4-octyl-3-oxaselenan-2-one (18) in good yield. This t ransformation represents the first reported example of intramolecular homolytic substitution by oxyacyl radicals at selenium. The analogous reaction involving 1-(benzylseleno)-4-dodecyl (phenyltelluro)formate ( 14) provides a complex mixture of products, while thermolysis of a ben zene solution of 14, 1-(benzylseleno)-5-tridecyl (phenyltelluro)format e (15) or 1-(benzylseleno)-6-tetradecyl (phenyltelluro)formate (16) at 160 degrees affords 2-octyltetrahydroselenophene (21), 2-octylselenan e (22), and 2-octylselenopane (23) in 43-94% yield, respectively. The formation of the saturated selenium-containing heterocycles 21-23 is m ost Likely to involve nucleophilic attack by the benzylseleno moiety w ith (decarboxylative) expulsion of phenyltelluride. The mechanisms of these transformations are discussed.