[CH2:1]([O:3][C:4](=[O:21])[C:5]([C:10]1[CH:15]=[CH:14][C:13]([NH2:16])=[C:12]([NH:17][CH3:18])[C:11]=1[C:19]#[N:20])([CH3:9])[C:6](=[O:8])[CH3:7])[CH3:2].[Br:22]Br>C(Cl)(Cl)Cl.C(OCC)(=O)C>[CH2:1]([O:3][C:4](=[O:21])[C:5]([C:10]1[CH:15]=[C:14]([Br:22])[C:13]([NH2:16])=[C:12]([NH:17][CH3:18])[C:11]=1[C:19]#[N:20])([CH3:9])[C:6](=[O:8])[CH3:7])[CH3:2]To a solution of 2-(4-amino-2-cyano-3-methylaminophenyl)-2-methyl-3-oxobutyric acid ethyl ester from Example 4 (9.02 g, 31.2 mmol) in CHCl3 (90 mL) was added bromine (4.98 g, 31.2 mmol) dropwise at ambient temperature. After the addition of bromine, the reaction mixture was diluted with ethyl acetate (800 mL). This solution was washed successively with sat. NaHCO3 solution and brine and dried. The residue after evaporation was purified by flash chromatography in hexanes/EtOAc 2:1 to yield 2-(4-amino-5-bromo-2-cyano-3-methylaminophenyl)-2-methyl-3-oxobutyric acid ethyl ester as an oil (6.06 g, 53%).
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