Abstract
4-(2-Nitrobenzylidene)-2-pyrazolin-5-ones (I) were best prepared by heating o-nitrobenzaldehyde and 2-pyrazolin-5-ones in acetic anhydride containing fused sodium acetate (cf. Erlenmeyer azlactone synthesis). Pyrazolones of type I were reductively cyclized with cyclohexene and palladium–charcoal, and gave 3a,4,9,9a-tetrahydro-9-hydroxy-1H-pyrazolo-[3,4-b]quinolines (II) which, as expected, were amphoteric compounds. Of the three other methods of reduction used in this study, two (zinc and acetic acid; sodium borohydride and palladium–charcoal) were capable of producing pyrazoloquinolines, but were less reliable. The other method employed (hydrazine hydrate and palladium–charcoal) caused degradation of the pyrazolone molecule in the two cases examined, and in both, bis(2-aminobenzylidene) hydrazine (V) was the reduction product isolated.
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