Triethylamine → 2-(5-Chloroisoxazole-3-carbonyl)-3-dimethylamino-acrylic acid ethyl ester

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A solution of 5-chloro-isoxazole-3-carboxylic acid (791 mg, 5.43 mmol) (preparation described in WO03093250 A2) in dichloromethane (27.2 mL, 0.2M) cooled to 0° C. was treated with oxalyl chloride (0.71 mL, 8.15 mmol, 98%) followed by a few drops of N,N-dimethylformamide. The reaction was allowed to gradually warm up to 25° C. The reaction was stirred at 25° C. overnight. At this time, the reaction was concentrated in vacuo. The resulting residue was dissolved in dichloromethane and re-concentrated twice to remove residual oxalyl chloride. The residue was then dissolved in dichloromethane (16 mL, 0.34M) and treated dropwise with a solution of ethyl-3-(dimethylamino)acrylate (0.79 g, 5.51 mmol) in triethylamine (1.6 mL, 11.47 mmol). The resulting red/orange reaction solution was heated to 60° C. overnight. At this time, the reaction was cooled to 25° C. and then partitioned between water (50 mL) and dichloromethane (100 mL). The organics were then washed with water (50 mL) and a saturated aqueous sodium chloride solution (50 mL), dried over magnesium sulfate, filtered and concentrated in vacuo. Biotage chromatography (40M column, 50-60% ethyl acetate/hexanes) afforded 2-(5-chloroisoxazole-3-carbonyl)-3-dimethylamino-acrylic acid ethyl ester (300.6 mg, 20%) as a red oil.

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