Studies on heterocyclic chemistry. Part IX. Reaction of 2-(carbonyl)-2H-azirines with hydrazine. A novel and unequivocal synthesis of 1,2,4-triazin-6-ones

The reaction of 2H-azirines containing a carbamoyl or alkoxycarbonyl group at C-2 with hydrazine and phenyl-hydrazine has been studied. 2-Aryl-2H-azirine-2-carboxamides produce tetrahydro-1,2,4-triazin-6-ones in moderate yield and aziridines, which are 1 : 1 adducts of the reactants, in small yield. Alkyl 2H-azirine-2-carboxylates and 2H-azirine-2-carboxamides which have no additional substituent at C-2 afford highly coloured 2-pyrazolin-5-one derivatives.