Citric Acid → 1H-Pyrazole-4-carboxylic acid, 5-cyclopropyl-1-(5-quinolinyl)- (HRID 353455)｜HGS AIchem

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Methyl-3-cyclopropyl-3-oxopropanoate (24.5 g, 0.1723 mole), N,N-dimethylformamide dimethyl acetal (21.56 g, 0.181 mole) and ethyl acetate (255 ml) were mixed together in a reaction flask under nitrogen and the resultant yellow solution held at 64-66° C. for 3 h 20 min to form α-[(dimethylamino)methylene]-β-oxo-cyclopropanepropanoic acid, (αZ)-methyl ester. The reaction solution was then cooled to room temperature. 5-Hydrazinoquinoline dihydrochloride (40.0 g, 0.1723 mole) was added to the yellow reaction solution containing α-[(dimethylamino)methylene]-β-oxo-cyclopropanepropanoic acid, (αZ)-methyl ester to form a yellow slurry. Triethylamine, TEA (60 ml, 0.431 mole, 2.5 equivalent) was added dropwise to the yellow slurry over 10 minutes. The reaction mixture self heated to about 35° C. After the addition was complete the resultant reaction mixture was heated to the temperature range 64-66° C. The slurry turned red upon heating. After 3 hours and 45 minutes, the reaction was essentially completed as measured by HPLC. The reaction mixture was cooled to room temperature and the following was added to the reaction mixture: ethyl acetate (170 ml), water (306 ml), citric acid (78.2 g, 0.407 mole) and Celite® filter aid (15 g). The quenched reaction liquors were stirred for 40 min. at 22-24° C., and then filtered to remove insoluble red material and filter aid. The filter cake was washed with a further 75 ml of ethyl acetate and the filtrate and wash were combined. The filter cake was discarded. The liquids were allowed to separate into two layers, a red organic layer (about 450 ml) and a dark red aqueous layer (about 550 ml). The red organic layer was concentrated under vacuum to a volume of about 150 ml. Propan-2-ol (150 ml) was added to the ethyl acetate concentrate and again concentrated to 150 ml under vacuum. A further quantity of propan-2-ol (150 ml) was added to the concentrate and this was finally concentrated to about 175 ml. The concentrate obtained contained the pyrazole ester, 5-cyclopropyl-1-quinolin-5-yl-1H-pyrazole-4-carboxylic acid methyl ester. Under a nitrogen atmosphere, water (50 ml) and 50% sodium hydroxide solution (22.5 ml, 0.431 mole) was added to the concentrate containing 5-cyclopropyl-1-quinolin-5-yl-1H-pyrazole-4-carboxylic acid methyl ester. A blue solution was formed and self-heating to about 31° C. was observed. The blue reaction mixture was heated to 64-66° C. and held under a nitrogen atmosphere for 4 h at this temperature. The reaction was found to be complete by HPLC testing and was cooled to room temperature. Concentrated hydrochloric acid 32% (about 33 ml) was added to the reaction mixture to adjust the pH to 4. Cooling was applied during the pH adjustment and the resultant yellow crystal slurry obtained was stirred at 15-20° C. for 1 h before isolation by filtration. The filter cake product was washed with water (80 ml) and dried under vacuum at 45° C. until all water was removed to afford 36.86 g 5-cyclopropyl-1-quinolin-5-yl-1H-pyrazole-4-carboxylic acid as pale pink crystals. Molar yield 76.6% based on input of 5-hydrazinoquinoline dihydrochloride.