The reaction was carried out with 6-bromo-3,4-dihydro-2H-benzo[b][1,4]oxazine (1.37 g, 6.4 mmol) and di-tert-butyl dicarbonate (1.676 g, 7.68 mmol) in the presence of triethylamine (970 mg) and 4-dimethylaminopyridine (78 mg, 0.64 mmol), stirred at room temperature in tetrahydrofuran (27 mL). mixture overnight. After completion of the reaction, the mixture was diluted with water (200 mL) and extracted with ethyl acetate (100 mL). The organic layer was washed sequentially with water (50 mL) and brine, dried over anhydrous sodium sulfate and concentrated to afford the target product tert-butyl 6-bromo-2H-benzo[b][1,4]oxazine-4(3H)-carboxylate (1.3 g, 65% yield) as a yellow oil.LC-MS analysis showed the [M-55]+ peak was located at m/z 258.1H NMR (400 MHz, DMSO- d6) δ 1.49 (s, 9H), 3.78 (t, J = 4.8 Hz, 2H), 4.21 (t, J = 4.4 Hz, 2H), 6.83 (d, J = 4.4 Hz, 1H), 7.12 (dd, J1 = 2.0 Hz, J2 = 8.4 Hz, 2H), 8.01 (s, 1H).
![6-Bromo-3,4-dihydro-2H-benzo[1,4]oxazine hydrochloride](/CAS/GIF/105655-01-4.gif)
![tert-butyl 6-broMo-2,3-dihydrobenzo[b][1,4]oxazine-4-carboxylate](/CAS/20180713/GIF/719310-31-3.gif)