Carbon tetrabromide → 3-(2,2-Dibromovinyl)-5-phenyl-4-(trifluoromethyl)isoxazole

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To a solution of carbon tetrabromide (12.24 g, 36.9 mmol) in dichloromethane (10 mL) at 0° C. was added a solution of triphenylphosphine (4.84 g, 18.5 mmol) in dichloromethane (10 mL), and the resulting mixture was stirred at 0° C. for 5 min. A solution of 5-phenyl-4-(trifluoromethyl)isoxazole-3-carbaldehyde (Intermediate I-13B, 1.59 g, 4.62 mmol) in dichloromethane (10 mL) was added via syringe, and the reaction mixture was stirred at 0° C. for 20 min. The reaction mixture was diluted with dichloromethane and washed with water. A white precipitate formed in the organic and was removed by vacuum filtrating. The filtrate was washed with a saturated aqueous solution of sodium bicarbonate, washed with a saturated aqueous solution of ammonium chloride, dried over anhydrous sodium sulfate, and concentrated. The residue was purified by flash silica gel chromatography using a mixture of ethyl acetate in hexane (1%-3%) to give 3-(2,2-dibromovinyl)-5-phenyl-4-(trifluoromethyl)isoxazole (1.21 g, 3.05 mmol, 66.0% yield) as a white solid. The product had an HPLC ret. time=3.10 min.−Column: Chromolith SpeedROD 4.6×50 mm (4 min.); Solvent A=10% MeOH, 90% H2O, 0.1% TFA; Solvent B=90% MeOH, 10% H2O, 0.1% TFA. LC/MS M+1=397.9. 1H NMR (500 MHz, CDCl3) δ ppm 7.43 (s, 1H), 7.52-7.56 (m, 2H), 7.56-7.61 (m, 1H), and 7.74 (d, J=7.49 Hz, 2H).

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