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STUDIES IN THE FIELD OF NITROGEN HETEROCYCLIC COMPOUNDS. PART XIV. SYNTHESIS OF PYRAZOLOPYRIDINE AND PYRAZOLOPYRIMIDINE DERIVATIVES
Balicki, Roman
, p. 1251 - 1261 (2007/10/02)
The reactions of various β-dicarbonyl compounds, β-diketones (1a-1g), β-ketoaldehydes (1h-1j) and β-ketoesters (1k-1w) with 3-amino-5-pyrazolone (2) in acetic acid solution were examined.On the basis of the experimental data obtained, a general scheme of this reaction was proposed.In the first, reversible step of the reaction, the intermediates (A, B, C) can be formed as a result of a competitive attack of three possible nucleophilic centers of 2 (C-4, N-1, -NH2) on a more positive carbonyl carbon atom of compound 1.Subsequent intermolecular cyclization of intermediates affords the corresponding pyrazolopyridines (3) and/or pyrazolopyrimidines (4, 6).It was found that the direction of cyclocondensation was noticeably affected by the nature of the dicarbonyl precursor, as well as the charge distribution and relative nucleophility of active centers of pyrazole ring within individual intermediates.
