Heterocyclic compounds from urea derivatives. Part XX. Adducts from carbonohydrazides and aroyl isothiocyanates and their cyclisation

Abstract

Aroyl isothiocyanates react additively in dimethylformamide with benzylidene- or 1-phenyl-carbonohydrazide, giving near-quantitative yields of mono-adducts, viz. 4-aroyl-1-(benzylideneamino)carbamoyl- or 4-aroyl-1-anilinocarbamoyl-3-thiosemicarbazides. These are cyclised to 3-aryl-5-mercapto-1,2,4-triazoles by alkalis, and to 2-aroylamido-5-hydroxy-1,3,4-thiadiazoles by acids. The mono-adducts of the parent carbonohydrazide with aroyl isothiocyanates cyclise spontaneously to 2-aroylamido-5-hydroxy-1,3,4-thiadiazoles under the conditions of their synthesis, but a symmetrical di-adduct from carbonohydrazide and benzoyl isothiocyanate is stable and isolable.