Organic heterocyclothiazenes. Part 6. Improved synthesis of trithiadiazepines from tetrasulphur tetranitride and alkynes

Abstract

In the reaction of tetrasulphur tetranitride, S₄N₄, with alkynes to give 1,3,5,2,4-trithiadiazepines, 1,3,5,2,4,6-trithiatriazepines, and 1,2,4- and 1,2,5-thiadiazoles, the yields of trithiadiazepines are often greatly improved (up to 8-fold) by the presence of Lewis acids, particularly titanium(IV) chloride. Thus the yield of dimethyl 1,3,5,2,4-trithiadiazepine-6,7-dicarboxylate (1) from dimethyl acetylenedicarboxylate (DMAD) is increased from 5 to 40%, formation of the trithiatriazepine (2) being totally suppressed. Trithiadiazepine formation is also much enhanced (up to 5-fold) at higher reaction temperatures (150–160 °C) than previously used (80–110 °C), though it varies very little with solvent polarity.