Hydrochloric Acid → 1-methyl-4-(trifluoromethyl)-1H-pyrazole-5-carboxylic acid

To a solution of diazomethane (0.781 g—generated from DIAZALD® (3.99 g) in diethyl ether (63 ml)), cooled by an ice/water bath, was added ethyl 4,4,4-trifluoro-2-butynoate (3.09 g) dropwise over 1 min. The cooling bath was removed and the mixture was stirred for 30 min when the solvent was removed under reduced pressure. The crude product was combined with the crude product from a similar experiment that was performed with 1,4 dioxane (5 ml) and n-pentane (15 ml) as the solvent and purified by column chromatography on silica gel to give a white solid. To a solution of a portion of this solid (100 mg) in 1,4-dioxane (2 ml) was added 2M hydrochloric acid (3 ml) and the mixture heated at reflux for 18 h, then concentrated hydrochloric acid (2 drops) was added and the mixture heated at reflux for a further 48 h. The mixture was concentrated in vacuo and the residue purified by mass directed preparative HPLC (Method A), to give the title compound, as a white solid (19 mg).