Synthesis and structure of 1-tert-butyl-substituted 3(5)-alkylpyrazoles from 2-chlorovinyl ketones

Reactions of alkyl, halomethyl 2-chlorovinyl ketones with tert -butylhydrazine in the presence of triethylamine afford unsymmetrical 1-( tert -butyl)-3- and -5-disubstituted pyrazoles. The reaction direction is governed by the ketone ability of the nucleophilic substitution of chlorine and of the dehydrochlorination leading to acetylene ketones. 2-Chlorovinyl ketones react with tert -butylhydrazine along two routes giving mixtures of 1-( tert -butyl)-3- and -5-alkylpyrazoles. The content of 3-alkyl-1-( tert -butyl)pyrazole in the formed isomers mixture grows up to 73% with growing length of the alkyl chain of the ketone and up to 87 and 94% at introducing halogen atom in the alkyl fragment of the chloroenone.