Synthesis of 1,3-disubstituted 5-chloro-1H-pyrazole-4-carbaldehydes was achieved by formylation of the corresponding 5-chloro-1H-pyrazoles under Vilsmeier-Haack conditions.

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Unsymmetrically substituted 1,3-and 1,5-dialkylpyrazoles and 1,3-dialkyl-5-chloropyrazoles were prepared. 2-Chlorovinyl ketones react with С 1 -С 8 -alkylhydrazines along two routes giving mixtures of 1-R'-3-R-and 1-R'-5-R-pyrazoles with the prevalence of 1,3-isomer. The proportion of 3-substituted 1-alkylpyrazole in the isomers mixture grows from 60 to 94-97% with growing length of the alkyl chain in the hydrazine. The alkylation of 1-unsubstituted 3(5)-alkylpyrazoles with alkyl bromides afforded predominantly (by 16-50%) 1,3-disubstituted pyrazoles. 1,3-Dialkyl-5-chloropyrazoles form from 2,2-dichlorovinyl alkyl ketones and functionalized alkylhydrazines. It was suggested to synthesize 1,3-dialkyl-substituted pyrazoles by dechlorination of unsymmetrically substituted 1,3-dialkyl-5-chloropyrazoles in the presence of complex nickel catalyst and water as the proton source.

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