Heterocyclic compounds from urea derivatives. Part XVIII. Adducts from aminoguanidines and aroyl isothiocyanates and their cyclisation
Equimolar quantities of aroyl isothiocyanates and aminoguanidine hydrochloride react additively in aqueous methanol affording excellent yields of 1-amidino-4-aroyl(thiosemicarbazides), isolable as hydrochlorides, picrates, or free bases. 1-Amidino-4-benzoyl(thiosemicarbazide) hydrochloride is cyclised by hydrochloric or orthophosphoric acid to 2-amino-5-benzamido-1,3,4-thiadiazole, by acetic anhydride to the corresponding acetyl derivative, and by alkali to 3-mercapto-5-phenyl-1,2,4-triazole. 1-Amino-2-phenylguanidine salts undergo an analogous series of reactions. The mechanism of these addition–cyclisations is discussed and correlated with those of comparable reactions.