Reaction of ethyl 2-diethoxymethyl-3-ethoxypropionate (I) and ethyl 2-methoxy methylene-3-ethoxypropionate (II) with arylhydrazines in ethanolic hydrochloric acid afforded ethyl 1-aryl-4-pyrazolecarboxylate (VIa-c), while the same reaction with ethyl 2-(ethoxymethoxymethyl)propionate (III) gave 1-aryl-4-methyl-2-pyrazolin-5-one (IX, XI, XIV). In case of reaction of I and II, from the results of isolation of corresponding amount of aniline to that of VI from the reaction mixture it seems

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... le to assume that pyrazoline derivative (V) would be resulted first which subsequently aromatized into Pyrazole with arylhydrazines.