[H-].[Na+].[Br:3][C:4]1[N:9]=[C:8]2[NH:10][C:11]([C@@H:13]3[CH2:17][CH2:16][CH2:15][N:14]3[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])=[N:12][C:7]2=[N:6][CH:5]=1.[CH3:25][Si:26]([CH2:29][CH2:30][O:31][CH2:32]Cl)([CH3:28])[CH3:27]>CN(C=O)C.O.CCOC(C)=O>[Br:3][C:4]1[N:9]=[C:8]2[N:10]=[C:11]([C@@H:13]3[CH2:17][CH2:16][CH2:15][N:14]3[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[N:12]([CH2:32][O:31][CH2:30][CH2:29][Si:26]([CH3:28])([CH3:27])[CH3:25])[C:7]2=[N:6][CH:5]=1.[Br:3][C:4]1[N:9]=[C:8]2[N:10]([CH2:32][O:31][CH2:30][CH2:29][Si:26]([CH3:28])([CH3:27])[CH3:25])[C:11]([C@@H:13]3[CH2:17][CH2:16][CH2:15][N:14]3[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])=[N:12][C:7]2=[N:6][CH:5]=1A 60% dispersion of NaH (75 mg, 1.9 mmol) was added to a stirred solution of (S)-tert-butyl 2-(6-bromo-1H-imidazo[4,5-b]pyrazin-2-yl)pyrrolidine-1-carboxylate (627 mg, 1.70 mmol) in DMF (15 mL) and the reaction was stirred for 1.5 h at room temperature. Then SEM-Cl (0.30 mL, 1.7 mmol) was added and the reaction was stirred overnight. The reaction was diluted with water (˜30 mL) and EtOAc (˜35 mL), the layers were separated and the organic layer was washed with brine (30 mL), dried (MgSO4), filtered and concentrated. The crude yellow oil was purified by flash chromatography (40 g SiO2, 20-30% EtOAc/hexanes) to yield (S)-tert-butyl 2-(5-bromo-1-((2-(trimethylsilyl)ethoxy)methyl)-1H-imidazo[4,5-b]pyrazin-2-yl)pyrrolidine-1-carboxylate (421 mg) as a clear colorless oil and (S)-tert-butyl 2-(6-bromo-1-((2-(trimethylsilyl)ethoxy)methyl)-1H-imidazo[4,5-b]pyrazin-2-yl)pyrrolidine-1-carboxylate (345 mg) as a clear colorless oil. The absolute regiochemistry of the SEM group was not established unambiguously, the names (and structures) may be exchanged in these intermediates.
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