Br[CH2:2][C:3]([O:5][C:6]([CH3:9])([CH3:8])[CH3:7])=[O:4].[Br:10][C:11]1[CH:22]=[CH:21][C:14]2[C:15](=[O:20])[O:16]C(=O)[NH:18][C:13]=2[CH:12]=1.C(=O)([O-])[O-].[K+].[K+].[OH-].[Na+].C[N:32](C=O)C>>[NH2:32][CH:2]([NH:18][C:13]1[CH:12]=[C:11]([Br:10])[CH:22]=[CH:21][C:14]=1[C:15]([OH:16])=[O:20])[C:3]([O:5][C:6]([CH3:9])([CH3:8])[CH3:7])=[O:4]tert-Butyl bromoacetate (1.34 mL, 9.1 mmol) was added to a solution of 7-bromo-2H-3,1-benzoxazine-2,4(1H)-dione from Step B (2 g, 8.26 mmol) and potassium carbonate (1.3 mg, 9.1 mmol) in DMF (20 mL) and stirred at ambient temperature for 4 h. 1 N NaOH (15 mL) was then added to the reaction and after 1 h, the mixture was partitioned between 0.5 N HCl and EtOAc. The organic layer was dried over Na2SO4, filtered, and concentrated to give the title compound in sufficient purity for use in the next step. MS: m/z=275 (M+1-tert-butyl).
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