Synthesis of (Pyrazol-4-yl)alkanones and Alkylpyrazole-4-Carbonitriles

Abstract

1-(5-Aminopyrazol-4-yl)alkan-1-ones and 5-alkylpyrazole-4-carbonitriles were obtained by reaction of 2-(1-ethoxyalkylidene)-3-oxoalkanenitriles (acrylonitriles) with hydrazines. The ratios of the various pyrazole products depended on the solvent used, and on the nature of the substituents on both the acrylonitrile and hydrazine reactants. In general, formation of pyrazole-4-carbonitriles was favoured by the use of acetic acid whereas use of ethanol favoured the formation of 1-(pyrazol-4-yl)alkan-1-ones. The use of 3-ethylacrylonitrile gave predominantly 3-ethylpyrazole-4-carbonitriles whereas acrylonitriles unsubstituted in the 3-position gave mainly 1-(pyrazol-4-yl)alkan-1-ones. The use of hydrazine gave exclusively pyrazole-4-carbonitriles irrespective of other factors, whereas use of methyl- and phenyl- hydrazines gave mixtures of varying composition depending on the acrylonitrile 3-substituent and the solvent. This synthesis provides a convenient route using mild conditions to novel pyrazole-4-carbonitriles and 1-(pyrazol-4-yl)alkan-1-ones which may have interesting biological properties.