(Aryltelluro)formates as precursors of alkyl radicals: Thermolysis and photolysis of primary and secondary alkyl (aryltelluro)formates

Alkyl (aryltelluro)formates are effective precursors of oxyacyl, methyl, and primary and secondary alkyl radicals. At room temperature, irradiation of a benzene solution of methyl (aryltelluro)formates 10-12, 2-methylpropyl (aryltelluro)formates 14 and 15, octyl (phenyltelluro)formate (17), cyclohexyl (aryltelluro)formates 19 and 20, 3 beta-cholestanyl (aryltelluro)formates 22 and 23, cholesteryl (phenyltelluro)formate (24) and benzyl (phenyltelluro)formate (27) with a 250-W low-pressure mercury lamp leads to the formation of oxyacyl radicals (34), which can be trapped by diphenyl diselenide to give the corresponding alkyl (phenylseleno)formates 13, 16, 18, 21, 24, 26, and 28 with excellent overall conversions. Thermolysis of these telluroformates at 160 degrees C in the dark leads to the formation of methyl and primary and secondary alkyl aryl tellurides 36-43 in excellent yields. Presumably, these transformations involve oxyacyl radicals, which undergo subsequent decarboxylation at the elevated temperature to afford alkyl radicals, which become involved in further radical chemistry. When 1-(benzylseleno)-5-hexyl (phenyltelluro)formate (44) was thermolysed under these conditions, 2-methylselenane (45) was observed as the sole selenium-containing product, demonstrating the synthetic utility of (aryltelluro)formates as alkyl radical precursors.