Polyfluoroalkyldithiocarboxylates react with dimethylacetylenedicarboxylate (DMAD) to give 2-polyfluoroalkyl-1,3-dithioles and/or 2-polyfluoroalkylidene-1,3-dithioles depending on the substituent at the thiolic sulfur atom and on the length of the polyfluoroalkyl chain. Amides of polyfluoroalkylthioncarboxylic acids with DMAD give 2-methoxy-2-polyfluoroalkyl-5-methoxycarbonylmethylene-thiazolidin-4-ones