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 stable Wittig reagents (II) react with episulfides (I) to produce mixtures of the fumarates and maleates (III), triphenylphosphine sulfide (IV), and the olefines (V).

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Stable Wittig reagents effectively reacted with episulfides to afford dialkyl fumarates and dialkyl maleates in good yields. The reaction probably occurred via attack of the ylide carbanion on episulfide’s sulfur to form a thiocarbonyl intermediate. The ylide further attacked this thiocarbonyl intermediate to give the final olefins.