Heterocyclic compounds from urea derivatives. Part XII. Ethoxycarbonylhydrazine as a source of 1,2,4-triazoles

Abstract

Interaction of equimolar quantities of carbodi-imides and ethoxycarbonylhydrazine in dimethylformamide yields 1-(NN′-diarylamidino)-2-ethoxycarbonylhydrazines, which are readily cyclised, with loss of ethanol, to 4-aryl-3-arylamino-5-hydroxy-1,2,4-triazoles. Ring-closure to the corresponding 5-ethoxy-heterocycles, with loss of water, occurred in one case.

S-Alkyl 1-ethoxycarbonyl-4-phenyl-3-isothiosemicarbazides, obtained from ethoxycarbonylhydrazine and phenyl isothiocyanate, and subsequent S-alkylation, are similarly convertible into 3-alkylthio-5-hydroxy-4-phenyl-1,2,4-triazoles.

Addition of aroyl isothiocyanates to ethoxycarbonylhydrazine yields 4-aroyl-1-ethoxycarbonyl-3-thiosemicarbazides. These are ring-closed in alkaline media, with loss of carbon dioxide and ethanol, to 3-aryl-5-mercapto-1,2,4-triazoles. The isolation of 1-ethoxycarbonyl-3-methylthio-5-phenyl-1,2,4-triazole in one example suggests that compounds of this type are formed intermediately in this cyclisation.