反应详情

A solution of hydroxylamine hydrochloride (400 mg, 5 8 mmol) in 1 ml water was added to a solution of NaOAc in 1 ml water. To the resulting solution was added 1-acetyl-4-bromo-2-hydroxy-5-methylbenzene (24) (1.14 g, 5 mmol) followed by addition of 15 ml EtOH. The reaction mixture was stirred at 80° C. for 1 h. After concentrated to half of it's volume, the reaction mixture was poured in to 60 ml ice-water. Precipitate formed was filtered, washed with water and dried to give 1.19 g (yield: 97.5%, purity>95%) 5-bromo-2-((hydroxyimino)ethyl)-4-methylphenol (25) as white solid. The above intermediate 25 (1.19 g, 4.875 mmol) was dissolved in 10 ml Ac2O, stirred at r.t. for 2 h and the reaction mixture turned to a white suspension. After filtration and wash with water 1.0 g 2-(4-bromo-2-hydroxy-5-methylphenyl)-1-azaprop-1-enyl acetate (26) were obtained. EA was added to the filtrate, washed with water. The org. phase was dried over sodium sulfate and concentrated to dryness to give another 370 mg of 26 as off-white solid. (total 1.37 g, yield: 98%, purity>95%). Neat 2-(4-bromo-2-hydroxy-5-methylphenyl)-1-azaprop-1-enyl acetate (26) (0.5 g, 1.748 mmol) was heated at 175° C. for 2 h then at 100° C. for 1 h. After cooling down to r.t., the dark brown solid was dissolved in DCM and subjected to silica gel flash chromatography (0-40% B, A: hexane; B: 50% EA in hexane) to give 6-bromo-3,5-dimethylbenz[d]isoxazole (27) (92 mg, yield: 23.3%; purity>95%) as yellow crystals.