Photolysis of S,C-sulfonium ylides derived from thioanisol, thiophene, benzothiophene, or dibenzothiophene provides product deriving from dicarbomethoxycarbene. In methanol, no rearrangement of the carbene to the ketene derivative is observed. Formation of dibenzothiophene and benzothiophene is quantitative. For the thiophene-based ylide, insertion of the carbene into the alpha-CH bond of thiophene is observed. Evidence is presented that supports formation of both singlet and triplet carbene.