Abstract. Electrochemical reductions of 4-aryl-and 4, 5-diaryl-l, 2, 3-thiadiazols (1-5) in acetonitrile/0, l M tetraalkylammonium-supporting-electrolyte at Hg-cathodes in the presence of ethylchloroformiate (CAE) yield (E)-S-(2-aryl) ethenyl-and S-(1, 2-diaryl) ethenyl-O-ethyl- thiocarbonates (1 a-5 a). The S-carboxylation proceeds via preformation of cyclic- voltammetric-and'H-nmrprovable CAE-complexes, ring-opening and Nz-elimination in a ...