NOVELTY - A 5-fluoro-1H-pyrazole is synthesized by preparing perfluoro-4-methyl-2-pentene by reacting hexafluoropropene in presence of catalyst to form dimer perfluoro-4-methyl-2-pentene, preparing perfluoro-2-methyl-2-pentene by isomerizing perfluoro-4-methyl-2-pentene into perfluoro-2-methyl-2-pentene, preparing perfluoro-2-methyl-2-penten-3-enolate by reacting perfluoro-2-methyl-2-pentene with water and base, and reacting intermediate compound with hydrazine.    USE - Synthesis of 5-fluoro-1H-pyrazole for preparing crop protection chemicals.    ADVANTAGE - Method is simple, safe and does not produce unwanted waste material.    DETAILED DESCRIPTION - A 5-fluoro-1H-pyrazole of formula (I) is synthesized by preparing perfluoro-4-methyl-2-pentene of formula (2) by reacting hexafluoropropene of formula CF2=CF(CF3) in presence of catalyst to form dimer perfluoro-4-methyl-2-pentene (step 1), preparing perfluoro-2-methyl-2-pentene of formula (3) by isomerizing perfluoro-4-methyl-2-pentene into perfluoro-2-methyl-2-pentene (step 2), preparing perfluoro-2-methyl-2-penten-3-enolate of formula (4) by reacting perfluoro-2-methyl-2-pentene with water and base (step 3), and preparing compound (I) by reacting intermediate compound with hydrazine of formula R1NH-NH2 (step 4).    Cat+=positive charged organic ion, alkaline metal cation or alkaline earth metal cation; and    R1=optionally halogenated 1-4C alkyl or cyclopropyl.    INDEPENDENT CLAIMS are included for:    (1) preparation of compound (IV) which involves steps 1-4; and    (2) use of hexafluoropropene for preparing pyrazole compounds.    R1=H, optionally halogenated 1-4C alkyl or cyclopropyl, preferably Me;    A1=C-R2;    R2=H, F, Cl, Br;    A2=C-R3 or N;    R3=H, Me, F or Cl, preferably H;    T=group of formulae (T1)-(T9);    R6=H, CN, NH3 or optionally substituted 1-6C alkyl, 1-6C alkyloxy, 1-6C alkylcarbonyl, 1-6C alkylsulfanyl, 1-6C alkylsulfinyl, 1-6C alkylsulfonyl;    n=0-2; and    Q=cyclopropyl, 1-cyano-cyclopropyl or benzyl.