Strategy for the Synthesis of pyrazolo[5,1-<Emphasis Type="Italic">d</Emphasis>][1,2,5]triazepinones,a new heterocyclic system

A preparative procedure has been developed for the synthesis of 4-oxo-7-phenyl-5,8-dihydro-4H-pyrazolo 5,1-d]1,2,5]triazepine-2-carbohydrazide, the first representative of a new heterocyclic system, by recyclization of methyl 4-oxo-6-phenyl-4H-pyrazolo5,1-c]1,4]oxazine-2-carboxylate with hydrazine hydrate.