Tetrahedron p. 4195 - 4202 (1987)
Update date:2022-07-31
Topics:
Maqestiau
Vanden Eynde
Treatment of ethyl (heteroalkylidene)aminopyrazole-4-carboxylates with hydrazine hydrate generally provides a ready synthetic route to 5-amino-4, 5-dihydropyrazolo [3,4-d] pyrimidin-4-ones, although ethyl 5-[(dimethylamino) alkylidene]aminopyrazole-4-carboxylates are unreactive. On the other hand, reactions between aminopyrazole-4-carboxhydrazides and orthoesters or amide acetal are more versatile : we observed formation of isomeric 2-pyrazolyl-1,3,4-oxadiazoles, as major compounds, either from triethyl orthoacetate and 1-methyl-5-aminopyrazole-4-carboxhydrazide or from dimethylacetamide dimethyl acetal and various heterocyclic precursors. The ring closure mechanism is discussed.
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