Homolytic substitution at selenium: ring closure of ω-(benzylseleno)alkyl radicals

Add time:07/17/2019    Source:sciencedirect.com

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% yield. The thiohydroxamic ester derived from 7-(benzylseleno)heptanoic acid affords the 7-membered heterocycle, selenopane in approximately 50% 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.

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