Unexpected Leaving Ability of (Phenyltelluro)formates in the
Presence of Internal Nucleophiles: Complications during Alkyl
and Oxyacyl Radical Generation in the Preparation of Sulfur- and
Selenium-Containing Heterocycles
posted on 1998-04-09, 00:00authored byMathew A. Lucas, Carl H. Schiesser
Irradiation of a benzene solution of 1-(benzylseleno)-3-undecyl
(phenyltelluro)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 transformation 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 benzene solution of 14, 1-(benzylseleno)-5-tridecyl
(phenyltelluro)formate (15) or 1-(benzylseleno)-6-tetradecyl (phenyltelluro)formate (16) at 160°
affords 2-octyltetrahydroselenophene (21),
2-octylselenane (22), and 2-octylselenopane (23)
in 43−94% yield, respectively. The formation of
the saturated selenium-containing heterocycles
21−23 is most likely to involve nucleophilic
attack
by the benzylseleno moiety with (decarboxylative) expulsion of
phenyltelluride. The mechanisms
of these transformations are discussed.