[CH3:1][O:2][C:3]1[CH:4]=[CH:5][C:6]2[O:11][CH2:10][C:9](=[O:12])[NH:8][C:7]=2[CH:13]=1.[H-].[Na+].Br[CH2:17][CH2:18][O:19][Si:20]([C:23]([CH3:26])([CH3:25])[CH3:24])([CH3:22])[CH3:21]>CN(C=O)C>[Si:20]([O:19][CH2:18][CH2:17][CH:10]1[C:9](=[O:12])[NH:8][C:7]2[CH:13]=[C:3]([O:2][CH3:1])[CH:4]=[CH:5][C:6]=2[O:11]1)([C:23]([CH3:26])([CH3:25])[CH3:24])([CH3:22])[CH3:21]To a solution of 6-methoxy-2H-1,4-benzoxazin-3(4H)-one (Intermediate 48) (800 mg, 4.5 mmol) in DMF (16 mL) was added sodium hydride (60% in mineral oil, 260 mg, 6.5 mmol). After 20 minutes, (2-bromoethoxy)(tert-butyl)dimethylsilane (1.4 mL, 6.5 mmol) was added and it was heated to 70° C. in the microwave for 40 minutes. The reaction mixture was partitioned between water (100 mL) and ethyl acetate (100 mL). The aqueous phase was extracted with ethyl acetate (4×50 mL). The combined organic phases were washed with water (6×250 mL), dried over magnesium sulfate and concentrated at reduced pressure to afford the product as a yellow oil which was used without further purification. (1.38 g, 91%).
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