Ma. Lucas et Ch. Schiesser, (ARYLTELLURO)FORMATES AS PRECURSORS OF ALKYL RADICALS - THERMOLYSIS AND PHOTOLYSIS OF PRIMARY AND SECONDARY ALKYL (ARYLTELLURO)FORMATES, Journal of organic chemistry, 61(17), 1996, pp. 5754-5761
Alkyl (aryltelluro)formates are effective precursors of oxyacyl, methy
l, and primary and secondary alkyl radicals. At room temperature, irra
diation of a benzene solution of methyl (aryltelluro)formates 10-12, 2
-methylpropyl (aryltelluro)formates 14 and 15, octyl (phenyltelluro)fo
rmate (17), cyclohexyl (aryltelluro)formates 19 and 20, 3 beta-cholest
anyl (aryltelluro)formates 22 and 23, cholesteryl (phenyltelluro)forma
te (24) and benzyl (phenyltelluro)formate (27) with a 250-W low-pressu
re 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 degre
es C in the dark leads to the formation of methyl and primary and seco
ndary alkyl aryl tellurides 36-43 in excellent yields. Presumably, the
se 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-(benzylsele
no)-5-hexyl (phenyltelluro)formate (44) was thermolysed under these co
nditions, 2-methylselenane (45) was observed as the sole selenium-cont
aining product, demonstrating the synthetic utility of (aryltelluro)fo
rmates as alkyl radical precursors.