Tetrahedron p. 2557 - 2566 (1993)
Update date:2022-07-31
Topics:
Benjamin, Lynda J.
Schiesser, Carl H.
Sutej, Katarina
The ring closure of a series of ω-(benzylseleno)alkyl radicals (1) has been studied.Thiohydroxamic esters derived from ω-(benzylseleno)alkanoic acids decompose smoothly, upon irradiation, with the loss of carbon dioxide to afford 5- and 6- membered selenium-containing rings in 78-95 percent yield.The thiohydroxamic ester derived from 7-(benzylseleno)heptanoic acid affords the 7-membered heterocycle, selenopane in approximately 50 percent yield.These reactions presumably involve intramolecular free radical homolytic substitution at selenium and appear to proceed readily for both primary and secondary carbon-centered radicals.The 5-(benzylseleno)hex-2-yl radical (1f) appears to ring close without stereoselectivity, to give a 1:1 mixture of cis- and trans-2,4-dimethyltetrahydroselenophene, a finding in keeping with molecular mechanics (MM2) calculations. Key Words: Homolytic Substitution; Selenium; Radical Ring Closure; Stereoselectivity; Thiohydroxamic Ester
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