[F:1][C:2]1[CH:3]=[CH:4][C:5]2[NH:10][CH2:9][CH2:8][O:7][C:6]=2[CH:11]=1.[Br:12][CH2:13][CH2:14][CH2:15]Br.C(=O)([O-])[O-].[Na+].[Na+]>CN(C=O)C.C(OCC)(=O)C>[F:1][C:2]1[CH:3]=[CH:4][C:5]2[N:10]([CH2:15][CH2:14][CH2:13][Br:12])[CH2:9][CH2:8][O:7][C:6]=2[CH:11]=1A mixture of 7-fluoro-3,4-dihydro-2H-benzo[b][1,4]oxazine (1.3 g, 1 eq, 8.49 mmol) obtained in step (iii) above, 1,3-dibromo propane (8.6 ml, 10 eq, 84.9 mmol) and anhydrous sodium carbonate (2.7 g, 3 eq, 25.4 mmol) in dry DMF (85 ml) was heated at 70° C. for 16 h. The reaction was diluted with ethyl acetate and washed with water and brine. The residue was chromatographed using ethyl acetate and hexane to afford the title compound (1.1 g, yield 47%) as viscous oil.
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