Me 3-methoxy-2-trifluoromethylacrylate, readily prepd. by Wittig reaction from Me 3,3,3-trifluoropyruvate, has been treated with a no. of aryl(or heteroaryl)hydrazines. Under mild base catalysis, the resulting 3-hydrazinoacrylates undergo consecutive hydrogen fluoride elimination and intramol. nucleophilic addn. to afford Me 1-(hetero)aryl-5-fluoropyrazole-4-carboxylates. 5-Aminopyrazoles have been obtained by direct reaction of Me 5-fluoro-1-phenylpyrazole-4-carboxylate with lithium amides, whereas 5-fluoro-1-phenylpyrazole-4-carboxamides have been formed by condensation of 5-fluoro-1-phenylpyrazole-4-carboxylic acid with amines. [on SciFinder (R)]