Step 4: To a solution of 6-bromo-2H-pyrido[3,2-b][1,4]oxazin-3(4H)-one (3.12 g, 13.7 mmol) in tetrahydrofuran (50 mL) was slowly added borane-tetrahydrofuran complex (33 mL, 33.0 mmol) at room temperature. The reaction mixture was heated to 90 °C and stirred continuously for 1.5 hours. Upon completion of the reaction, methanol (2.0 mL) was slowly added to quench the reaction and stirring was continued at 90 °C for 20 minutes. Subsequently, the reaction mixture was concentrated under reduced pressure to remove the solvent. The residue was dissolved in ethyl acetate, washed with saturated aqueous sodium bicarbonate, dried over anhydrous magnesium sulfate, and finally concentrated under reduced pressure to afford 6-bromo-3,4-dihydro-2H-pyrido[3,2-B][1,4]oxazine (3.17 g, 100% yield), the product was a yellow powder.1H-NMR (DMSO-d6) δ: 7.04 (1H, br s). 6.69 (1H, d, J = 7.8 Hz), 6.40 (1H, d, J = 7.8 Hz), 3.91 (2H, t, J = 4.2 Hz), 3.19-3.23 (2H, m).LC/MS (Method A): 1.44 min, [M + H]+ = 215.2.
![6-BROMO-2H-PYRIDO[3,2-B][1,4]OXAZIN-3(4H)-ONE](/CAS/GIF/337463-88-4.gif)
![6-BROMO-3,4-DIHYDRO-2H-PYRIDO[3,2-B][1,4]OXAZINE](/CAS/GIF/959992-62-2.gif)