Diethyl Oxalate → 1-(6-Methoxy-3-pyridyl)-5-(1-methylpyrrol-2-yl)pyrazole-3-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

Under cooling at −78° C., 1.0 M lithium bis(trimethylsilyl)amide in tetrahydrofuran (10.4 mL) was added to 1-(1-methylpyrrol-2-yl)-1-ethanone (1.19 mL) in tetrahydrofuran (10 mL), followed by stirring for 35 minutes. Diethyl oxalate (2.05 mL) was added to the reaction mixture, and the resultant mixture was gradually returned to room temperature, followed by stirring at room temperature for 2.5 hours. To the reaction mixture, triethylamine (1.64 mL), 5-hydrazino-2-methoxypyridine hydrochloride (2.52 g) obtained from Referential Example 1, and ethanol (50 mL) were added. The mixture was refluxed under heat for 2.5 days. Acetic acid (5 mL) was added thereto, and the reaction mixture was refluxed under heat for 3 days, and then cooled in air. The reaction solvent was removed under reduced pressure. The residue was partitioned by use of ethyl acetate and saturated aqueous sodium hydrogencarbonat, and the aqueous layer was extracted with ethyl acetate. The organic layers were combined, and then dried over sodium sulfate anhydrate, followed by filtration. The solvent was removed under reduced pressure, and the residue was purified through silica gel column chromatography (ethyl acetate-hexane), to thereby give 1-(6-methoxy-3-pyridyl)-5-(1-methylpyrrol-2-yl)pyrazole-3-carboxylic acid ethyl ester as an oily product (2.70 g, 82%). Aqueous 1N sodium hydroxide (21 mL) was added to the thus-obtained ethyl ester (2.70 g) in ethanol (20 mL), followed by stirring at room temperature for 26 hours. The reaction mixture was partitioned by use of aqueous 1N hydrochloric acid and ethyl acetate, and the aqueous layer was extracted again with ethyl acetate. The organic layers were combined, and then dried over magnesium sulfate anhydrate, followed by filtration. The solvent was removed under reduced pressure, to thereby give the title compound as an amorphous solid (2.57 g, quantitative amount). Without further purification, the compound was subjected to the following reaction.

Provenance & Evidence