Synthesis of trifluoromethylated pyrazoles from trifluoromethylenaminones and monosubstituted hydrazines

Cyclocondensation of monosubstituted hydrazines 2a–c with trifluoromethylenaminones 1a–c afforded 3-CF3 and (or) 5-CF3 pyrazoles 3–6. Addition of N-methylhydrazine to enaminone led to 3-CF3 pyrazole as the major product, whereas phenylhydrazine gave regiospecific formation of 5-CF3 pyrazole. ural assignment of regioisomers is based on 13C NMR chemical shifts, long-range carbon–fluorine and hydrogen–fluorine coupling constants and 1H–1H NOE. razole 4ac was characterized by X-ray diffraction analysis.