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Synthesis of 5-amino-4,5-dihydropyrazolo [3,4-d] pyrimidin-4-ones and related isomeric systems : Part II. Ring closure reactions

✍ Scribed by A. Maqestiau; J.-J. Vanden Eynde

Book ID: 104203023
Publisher: Elsevier Science
Year: 1987
Tongue: French
Weight: 432 KB
Volume: 43
Category: Article
ISSN: 0040-4020
DOI: 10.1016/s0040-4020(01)83460-8

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✦ Synopsis

Abstrat -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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