Dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate is a sulphur-containing heterocyclic building block. It has been reported to be formed during the reaction of 1,3-dithiolan-2-thiones with dimethyl acetylenedicarboxylate. It is formed as major product during the reaction of ethylene trithiocarbonate with dimethyl acetylenedicarboxylate.