The reactions of Wittig reagents with episulfides gave symmetrical olefins and triphenylphosphine sulfide in moderate yields. The same olefins were obtained by reactions of Wittig reagents with elemental sulfur. These reactions might proceed through thiocarbonyl intermediates, the existence of which was confirmed by Diels–Alder reactions with dienes.

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The methylenephosphoranes (I) undergo coupling reaction in the presence of selenium (II) to form the olefins (IV) and triphenylphosphine selenide (V) via the selenoaldehydes or selenoketones (III).