[C:1]([O:5][C:6](=[O:20])[NH:7][C@@H:8]1[C:14](=[O:15])[NH:13][C:12]2[CH:16]=[CH:17][CH:18]=[CH:19][C:11]=2[NH:10][CH2:9]1)([CH3:4])([CH3:3])[CH3:2].[CH3:21][Si]([N-][Si](C)(C)C)(C)C.[Li+].CI>O1CCCC1>[C:1]([O:5][C:6](=[O:20])[NH:7][C@@H:8]1[C:14](=[O:15])[N:13]([CH3:21])[C:12]2[CH:16]=[CH:17][CH:18]=[CH:19][C:11]=2[NH:10][CH2:9]1)([CH3:4])([CH3:2])[CH3:3]To a solution of 5.0 g (18 mmol) (S)-(2-oxo-2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepin-3-yl)-carbamic acid tert-butyl ester in 80 ml of tetrahydrofuran at −75° C. 18 ml (18 mmol) of lithium bis(trimethylsilyl)amide solution (1M in tetrahydrofurane) was added. After stirring for 30 min at −75° C. the mixture was allowed to reach room temperature and 3.07 g (21.6 mmol) of methyl iodide was added. The mixture was stirred for 2.5 hours at room temperature and concentrated in vacuo. The residue was distributed between 1M NaHSO4 solution and ethyl acetate. The combined organic layers were reextracted with water and dried (MgSO4). After evaporation of the solvent, (S)-(1-methyl-2-oxo-2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepin-3-yl)-carbamic acid tert-butyl ester was obtained in sufficient purity for the next step.
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