Acetonitrile → 1H-Pyrazole-5-carboxylic acid, 3-bromo-1-(3-chloro-2-pyridinyl)-4,5-dihydro-, ethyl ester

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Reaction Steps

To a 500 mL flask, acetonitrile (200 mL), ethyl 1-(3-chloro-2-pyridinyl)-3-oxopyrazolidine-5-carboxylate (21.28 g, 94%, 74.17 mmol) and phosphoryl bromide (14.88 g, 51.92 mmol) were added. The reaction mixture was heated to reflux for 2 hours. 150 mL solvent was distilled from the reaction mixture. The concentrated reaction mixture was added to the mixture of sodium carbonate (10.56 g, 155.7 mmol) and water (40 mL). The reaction mixture was stirred for 20 minutes until no more gas released, and then diluted with dichloromethane (100 mL), stirred for 50 minutes. The mixture was extracted with dichloromethane (3×200 mL). The combined organic layers were washed with water, dried over anhydrous magnesium sulfate, and concentrated by rotary evaporator to give ethyl 3-bromo-1-(3-chloro-2-pyridinyl)-4,5-dihydro-1H-pyrazole-5-carboxylate (25.73 g) as a amber oil in 97% yield. HPLC area normalization method content is 93% (Analytical condition: chromatographic column: ZORBAX Eclipse XDB-C8 4.6×150 mm 5 μm, mobile phase:the ratio of acetonitrile to water is 70:30).

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