[CH2:1]([O:3][C:4]([C:6]1[NH:7][C:8]([SH:11])=[N:9][CH:10]=1)=[O:5])[CH3:2].[CH2:12](N(CC)CC)C.IC.[CH3:21][Si:22]([CH2:25][CH2:26][O:27][CH2:28]Cl)([CH3:24])[CH3:23]>C(Cl)Cl>[CH2:1]([O:3][C:4]([C:6]1[N:7]([CH2:28][O:27][CH2:26][CH2:25][Si:22]([CH3:24])([CH3:23])[CH3:21])[C:8]([S:11][CH3:12])=[N:9][CH:10]=1)=[O:5])[CH3:2]To a solution of 2-mercapto-3H-imidazole-4-carboxylic acid ethyl ester (1.0 g, 5.8 mmol) in 15 mL of DCM was added triethylamine (NEt3) (1.0 mL, 7.2 mmol) and iodomethane (0.4 mL, 6.4 mmol) and the mixture stirred for 3 h at RT. The mixture was cooled in an ice bath, NEt3 (1.0 mL, 7.2 mmol) and SEM-Cl (1.2 mL, 6.4 mmol) was added, the mixture stirred for 3 hours at RT and then an additional portion of NEt3 (0.5 mL, 3.6 mmol) and SEM-Cl (0.6 mL, 3.2 mmol) was added and the mixture stirred for 8 h at RT. The mixture was diluted with 50 mL of DCM and washed with NaHCO3 (2×60 mL) and brine (60 mL) and dried over Na2SO4. Flash chromatography of the residue on Si gel with 30% EtOAc/hexanes gave the title compound as a colorless oil (1.0 g, 55%). Mass spectrum (ESI, m/z): Calcd. for C13H24N2O3SSi, 317.1 (M+H). found 316.7.
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