CHEMISTRY OF SUBSTITUTED PYRAZOLO[1,5-ALPHA]PYRIMIDINES .5. (5')-YL]-4,7-DIHYDROPYRAZOLO[1,5-ALPHA]PYRIMIDINES FROM -DIMETHYLAMINOVINYL)PYRAZOLO[1,5-ALPHA]PYRIMIDINES - ELUCIDATION OF THE REACTION-MECHANISM THROUGH NMR-SPECTROSCOPY AND X-RAY-DIFFRACTION ANALYSIS

The reaction of -dimethylaminovinyl)pyrazolo[1,5-alpha]pyrimidines 1a, b with hydrazine hydrate in acetic acid solution gave rise to (5')-yl] -4,7-dihydropyrazolo[1,5-alpha]pyrimidines 3a,b, a result very similar to the intramolecular cyclization previously reported for the corresp onding 6-acetyl derivatives 1c,d. Treatment of compounds 3a,b with dim ethyl sulfate gave rise to a mixture of the N-methyl derivatives 4a,b and 5a,b whose structures have; been unambiguously established on the basis of NMR spectroscopy and confirmed by the X-ray structure of comp ound 4a, The same reaction carried out with methylhydrazine led to a m ixture of 6-(1'-methylpyrazol-3'-yl)-7-oxo- 6a,b and l)-7-oxo-4,7-dihy dropyrazolo-[1,5-alpha]pyrimidine 7a,b in which the former were predom inant, When the reaction was carried out in ethanol, a different regio selectivity was observed leading to the isolation of the open-chain in termediate compounds 11-13 which in turn give rise, predominantly, to the pyrazolopyrimidine derivative 7a. A reaction pathway based on the X-ray structure of compound 11 is proposed.