General procedure for the synthesis of 6-bromo-3,4-dihydro-2H-benzo[1,4]oxazines from 6-bromo-2H-1,4-benzoxazin-3(4H)-ones: at room temperature, the borane-tetrahydrofuran complex (13.2 mL of a 1 M solution of tetrahydrofuran, 13.2 mmol) was added batchwise to intermediate 6 (2.0 g, 8.0 mmol) in a tetrahydrofuran ( 50 mL) solution. The reaction mixture was stirred for 10 minutes at room temperature and then heated to reflux for 1 hour, followed by cooling to room temperature. The reaction mixture was cooled in an ice bath and the reaction was quenched sequentially with water (20 mL) and 2 N aqueous sodium hydroxide solution (20 mL). The solvent was removed by rotary evaporator and the resulting mixture was diluted with water (100 mL). The aqueous phase was extracted with ethyl acetate (100 mL), the organic phase was washed with saturated brine (100 mL), dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to give 6-bromo-3,4-dihydro-2H-benzo[1,4]oxazine as a brown oil (2 g, quantitative yield). NMR hydrogen spectrum (DMSO-d6) δ: 3.36-3.44 (2H, multiple peaks), 3.81 (1H, broad single peak), 4.18-4.25 (2H, multiple peaks), 6.68 (3H, multiple peaks).
![6-Bromo-3,4-dihydro-2H-benzo[1,4]oxazine hydrochloride](/CAS/GIF/105655-01-4.gif)