A detailed study of the reactions of phosphorus pentasulfide and Lawesson's reagent with a series of 4, 5-bis (RCOCH2S)-1, 3-dithiole-2-thiones (R= Ph, 4-MeOC6H4, 4-Br C6H4, Me) has been carried out. These reactions lead to fusion of either an unsaturated 1, 4-dithiin ring or a thiophene to the dithiole; the former in higher yield, while the latter is a significant product in the reactions with Lawesson's reagent; as well as small amounts of minor ...