Synthesis of fluorinated N-arylpyrazoles with perfluoro-2-methyl-2-penteneand arylhydrazines

Reactions of arylhydrazines (phenyl, 2-nitrophenyl, 4-nitrophenyl, 2,4-dini trophenyl, pentafluorophenyl, 4-trifluoromethyl-2,3,5,6-tetrafluorophenylhy drazine or 4,4'-dihydrazinooctafluorobiphenyl) with perfluoro-2-methyl-2-pe ntene in the presence of triethylamine have effectively produced 1-aryl-per fluoro-3-ethyl-4-methylpyrazole and 1-aryl-perfluoro-5-ethyl-4-methylpyrazo le in various ratios depending on the reaction conditions and arylhydrazine used. Syn- and anti-aminoimines which might be the intermediates for pyraz oles have been isolated under appropriate conditions. The routes of formati on for these products and the role of triethylamine have been discussed. Th e reaction of perfluoro-2-methyl-2-pentene with phenylhydrazine has been in vestigated in detail. The structure of 3-fluoro-5-pentafluoroethyl-1-phenyl -4-trifluoromethylpyrazole has been elucidated by X-ray crystallography. (C ) 1999 Elsevier Science S.A. All rights reserved.