[Br:1][C:2]1[CH:3]=[CH:4][C:5]2[O:6][CH2:7][C:8](=[O:12])[NH:9][C:10]=2[N:11]=1.[CH3:13][O:14][C:15]1[CH:22]=[C:21]([O:23][CH3:24])[CH:20]=[CH:19][C:16]=1[CH2:17]Cl.C([O-])([O-])=O.[Cs+].[Cs+]>CN(C=O)C>[Br:1][C:2]1[CH:3]=[CH:4][C:5]2[O:6][CH2:7][C:8](=[O:12])[N:9]([CH2:17][C:16]3[CH:19]=[CH:20][C:21]([O:23][CH3:24])=[CH:22][C:15]=3[O:14][CH3:13])[C:10]=2[N:11]=1A suspension of 6-bromo-4H-pyrido[3,2-b][1,4]oxazin-3-one (0.412 g, 1.8 mmol) and 2,4-dimethoxybenzyl chloride (0.336 g, 1.8 mmol; freshly prepared according to U.S. Pat. No. 5,817,653) in DMF (5 mL) was treated with Cs2CO3 (1.76 g, 3 eq.). The mixture was stirred at rt for 2 h, partitioned between EA and water. The aq. phase was extracted with EA and the combined org. layers washed with water, and brine, dried over MgSO4 and concentrated. The residue was purified by FC (Hept/EA 1:1) to give the title intermediate as a colourless oil (0.61 g, 90% yield).
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