Hydrochloric Acid → ethyl 1-cyclopentyl-5-methyl-1H-pyrazole-4-carboxylate

Participants

Reaction Steps

To a solution of 1-cyclopentylhydrazine-2-carboxylic acid tert-butyl ester (18.4 g, 92 mmol) in a mixture of ethanol (300 mL) and conc. HCl (7.7 mL, 92 mmol) was added ethyl 2-acetyl-3-(dimethylamino)acrylate (25.5 g, 0.138 mol). The resulting mixture was refluxed for 2 h. The reaction was concentrated in vacuo, dissolved in CH2Cl2 (300 mL), washed with satd NaHCO3, and brine, dried (Na2SO4), concentrated in vacuo and purified by chromatography on silica gel to give ethyl 1-cyclopentyl-5-methyl-1H-pyrazole-4-carboxylate (15.6 g, 76% yield). 1H NMR (400 MHz, DMSO-d6): δ 8.15 (s, 1 H), 4.61 (m, 1 H), 4.15 (q, J=8 Hz, 2 H), 2.29 (s, 3 H), 2.04-1.97 (m, 2 H), 1.89-1.85 (m, 2 H), 1.78-1.71 (m, 2 H), 1.62-1.59 (m, 2 H), 1.23 (t, J=8 Hz, 3 H).

Provenance & Evidence