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Oxyselenylation of 4‐substituted 5‐hexen‐1‐ols 1 with benzeneselenenyl trifluoromethanesulfonate proceeds by intramolecular exo cyclization stereoselectively to give 3‐substituted trans ‐ or cis ‐2‐(phenylselenenylmethyl)tetrahydropyrans 3 . Formation of the trans isomers is favored when the substituents contain alkyl or phenyl substituents in the 4‐position, whereas the cis isomers predominate when the substituents are alkoxyalkyl, alkoxyl, acyl, and hydroxyl. The mechanism of the trans and cis stereoselectivity is explained by steric and electronic effects in the phenylseleniranium intermediates, 7 and 8 .
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INOUE et al. (1994) studied this question.
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