Regioselective synthesis of fused pyrazolo[1,5-a]pyrimidines by reaction of 5-amino-1H-pyrazoles and β-dicarbonyl compounds containing five-membered rings
Reactions of 3-substituted-5-amino-1H-pyrazoles with 2-acetylcyclopentanone or 2-ethoxycarbo-nylcyclopentanone lead to the regioselective formation of a new series of cyclopentapyrazolo[1,5-a]pyrimidines in good yields. When 2-acetylbutyrolactone was used, the reaction provided 6-(2-hydroxyethyl)pyrazolo[1,5-a]pyrimidinone and/or the intermediate (3Z)-3-1-[(5-R-1H-pyrazol-3-yl)amino]ethylidene}-4