Wittig reagents were successfully changed to symmetrical olefins when treated with elemental selenium. The reaction proceeds through a selenocarbonyl intermediate, which existence was confirmed by Diels-Alder reaction.
Selenabicyclo[2.2.1]heptenes reacted with elemental selenium to produce unusual bicyclic diselenides in 30-40% yield. The reaction of phosphonium ylides with excess of elemental selenium also afforded bicyclic diselenides in good yields. The reactions might proceed via biradical intermediates.
Okuma, Kentaro; Kojima, Kazuki; Kaneko, Isao, Journal of the Chemical Society. Perkin transactions I, 1994, # 15, p. 2151 - 2160