Novel polyfluoroalkylated pyrazoles from 2-polyfluoroacylcycloalkanones and hydrazines: syntheses and unequivocal molecular structure assignment

Abstract

The reaction between 2-trifluoroacetylcycloalkanones and methylhydrazine or phenylhydrazine exclusively yields 3-CF 3 -pyrazoles. When the chain length of the polyfluorinated substituent in R F C(O) group increases, 5-R F -pyrazoles are isolated. The reaction of 2-trifluoroacetylcyclohexanone with 2-hydrazinopyradine gives 5-hydroxypyrazoline, an intermediate in the formation of 5-CF 3 -pyrazoles. The regiochemistry of the condensation is probably controlled by the nucleophilicity of the terminal nitrogen in the mono substituted hydrazines and by the steric requirements of the R F group in the 1,3-diketones. Polymethylene chain containing pyrazoles obtained from the 1,3-diketones in question and hydrazine prefer the 3-R F tautomeric form, irrespective of carbocyclic ring size and polyfluoroalkyl group chain length.Key words: polyfluorinated 1,3-diketones, hydrazines, isomeric pyrazoles, molecular structure.