[Br:1][C:2]1[CH:11]=[C:10]2[C:5]([C:6](=[O:12])[CH2:7][CH2:8][O:9]2)=[CH:4][CH:3]=1.CS(O)(=O)=O.[N-:18]=[N+]=[N-].[Na+].[OH-].[Na+]>C(Cl)Cl.O>[Br:1][C:2]1[CH:3]=[CH:4][C:5]2[C:6](=[O:12])[NH:18][CH2:7][CH2:8][O:9][C:10]=2[CH:11]=1A solution of 7-bromochroman-4-one (340 mg, 1.5 mmol) and methanesulfonic acid (3 mL, 23.0 mmol) in DCM was cooled to 0° C. and treated with NaN3 (146 mg, 2.25 mmol) portionwise, while maintaining the internal temperature below 5° C. The reaction was then stirred at 0° C. for 4 h. At completion, the reaction was slowly neutralized with 8 N aq. NaOH, then diluted with DCM (20 mL) and water (20 mL). The layers were separated and the organics were dried over MgSO4, filtered and evaporated to afford 8-bromo-3,4-dihydrobenzo[f][1,4]oxazepin-5(2H)-one (370 mg, 100% yield). MS (EI) m/z=242.1 [M+1]+.
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