Features of Synthesis of 5(3)-Polyfluoromethylpyrazole-3(5)-Carbaldehyde and Their Dimethyl Acetals

Reactions of difluoroacetyl- and trifluoroacetylpyruvaldehyde dimethyl acetals with methyl and phenylhydrazine in methanol occur regioselectively and make it possible to obtain N-methyl- and N-phenyl-substituted 5-polyfluoromethylpyrazole-3-carbaldehyde and their dimethyl acetals in good yields. Regioisomeric N- methyl- and N-phenyl-substituted 3-polyfluoromethylpyrazole-5-carbaldehyde and their dimethyl acetals were synthesized in moderate yields by reacting the same reagents in trifluoroethanol or acetic acid.