Synthesis of fluorinated pyrazole derivatives from beta-alkoxyvinyl trifluoroketones

1.1.1-Trifluoro-4-ethoxy-3-butane-2-one, 3-trifluoroacetyl-3, 4-dihydro-2H- pyran or furan reacted readily with pentafluorophenylhydrazine or per(poly) fluoroacectylhydrazine RtCO-NHNH2 (R-1: BrCF2, C3F7) to give N-substituted- 5-hydroxy-5-trifluoromrthyl I heterocycles Y-N-N=CH-CH(R)C(OH)CF3 (Y: H, Ar -f - or RtCO), which were dehydrated by treatment with P2O5 or SOCl2 to for m N-substituted 5-trifluoromethyl pyrazoles Y-N-N=CH-C(R)=C CF3 (Y: H, Ar-f - or RtCO) in good yields. [GRAPHICS] (C) 2001 Elsevier Science B.V. All rights reserved.