To a mixture of (Z)—N-hydroxy-5-phenyl-4-(trifluoromethyl)isoxazole-3-carbimidoyl chloride (Intermediate 13, 0.221 g, 0.646 mmol) and 4-(7-vinyl-2H-chromen-4-yl)morpholine (Preparation 53A, 0.535 M in dichloromethane, 1.21 mL, 0.646 mmol) at 0° C. was added triethylamine (0.108 mL, 0.776 mmol) dropwise over 3 min. The ice-bath was removed, and the reaction mixture was stirred at room temperature for 30 min. The reaction mixture was diluted with dichloromethane (30 mL), washed with water (15 mL), dried over anhydrous sodium sulfate, and concentrated to give a foamy solid. The product mixture was dissolved in dichloroethane (3 mL), TFA (0.075 mL, 0.970 mmol) was added, and the resulting solution was heated at 80° C. for ˜60 min. The reaction mixture was diluted with dichloromethane (30 mL), washed with a saturated aqueous solution of sodium bicarbonate (15 mL), and dried over anhydrous sodium sulfate. Concentration under reduced pressure followed by purification by flash silica gel chromatography using a mixture of ethyl acetate in hexane (5%-12%-20%) afforded 3-(5-phenyl-4-(trifluoromethyl)isoxazol-3-yl)-7-vinyl-4H-chromeno[3,4-d]isoxazole (0.033 g, 0.078 mmol, 12% yield) as a white solid. The product had an HPLC ret. time=3.93 min. (condition A); LC/MS M+1=411.0.
