Dimethyl acetylenedicarboxylate → 5-Hydroxy-1H-pyrazole-3-carboxylic acid methyl ester

Participants

Reaction Steps

Hydrazine monohydrate (6.7 g, 210 mmol) was added to a solution of dimethyl acetylenedicarboxylate (24.7 g, 175 mmol) in toluene (90 ml) at 0° C., and the thus-obtained mixture was gradually temperature-increased up to room temperature, stirred for 2 hours and further stirred under heating at 130° C. for 4 hours. After completion of the reaction, a precipitated solid was filtered and washed with diethyl ether, to give a white solid of methyl 3-hydroxypyrazole-5-carboxylate (18.2 g, yield: 73.8%). mp: 229-231° C.; 1H-NMR (DMSO-d6, DMSO, ppm): δ 3.79 (s, 3H), 5.91 (s, 1H), 10.10-10.45 (br s, 1H). (Hydroxy proton was not assigned.)

Provenance & Evidence