[O:1]1[CH2:6][C:5](=[O:7])[NH:4][C:3]2[N:8]=[CH:9][CH:10]=[CH:11][C:2]1=2.C1C(=O)N([Br:19])C(=O)C1.O>CN(C=O)C>[Br:19][C:10]1[CH:9]=[N:8][C:3]2[NH:4][C:5](=[O:7])[CH2:6][O:1][C:2]=2[CH:11]=1To a solution of 5.6 g 2H-pyrido[3,2-b]-1,4-oxazin-3(4H)-one dissolved in 85 ml of DMF under nitrogen is added 7.96 g NBS in 50 ml of DMF. This is allowed to stir at room temperature overnight. To this is added 35 ml of water and the mixture is chilled The solid material which separates is filtered and washed with 3×100 ml H2O. This is then dried under vacuum at 70° C. and then used directly in the next step.
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