[CH3:1][C:2]1[C:10]2[NH:9][C:8](=[O:11])[NH:7][C:6]=2[CH:5]=[C:4]([CH3:12])[CH:3]=1.[H-].[Na+].Br[CH2:16][C:17]([O:19][C:20]([CH3:23])([CH3:22])[CH3:21])=[O:18]>CN(C=O)C.O>[CH3:1][C:2]1[C:10]2[NH:9][C:8](=[O:11])[N:7]([CH2:16][C:17]([O:19][C:20]([CH3:23])([CH3:22])[CH3:21])=[O:18])[C:6]=2[CH:5]=[C:4]([CH3:12])[CH:3]=1To a stirred solution of 4,6-dimethyl-1,3-dihydro-2H-benzimidazol-2-one from Step A (7.15 g, 44.1 mmol) in DMF (200 mL) was added sodium hydride (1.76 g of a 60% dispersion in mineral oil, 44.1 mmol) over 2 min. The mixture was stirred for 20 min, then tert-butyl bromoacetate (8.17 g, 41.9 mmol) in DMF (40 mL) was added and stirring was continued for 1 h. The reaction mixture was diluted with H2O (400 mL) carefully and a solid precipitated. The mixture was aged for 5 min, then filtered to give a crude solid, which was purified by silica gel chromatography, eluting with a gradient of CH2Cl2:EtOAc-100:0 to 40:60, to provide the title compound. MS: m/z=277 (M+1).
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