[C:1](N1C=CN=C1)(N1C=CN=C1)=[S:2].[C:13]([Si:17]([CH3:28])([CH3:27])[O:18][C:19]1[CH:24]=[CH:23][C:22]([NH2:25])=[C:21]([NH2:26])[CH:20]=1)([CH3:16])([CH3:15])[CH3:14]>O1CCCC1>[SH:2][C:1]1[NH:26][C:21]2[CH:20]=[C:19]([O:18][Si:17]([C:13]([CH3:16])([CH3:15])[CH3:14])([CH3:28])[CH3:27])[CH:24]=[CH:23][C:22]=2[N:25]=11,1′-Thiocarbonyldiimidazole (1.87 g, 10.5 mmol) is added by portions to a solution of 4-(tert-butyl-dimethyl-silanyloxy)-ortho-phenylenediamine (2.5 g, 10.5 mmol) in 25 ml of tetrahydrofuran and the mixture is stirred at room temperature for 16 hours. The reaction mixture is then concentrated under reduced pressure, dissolved in 300 ml of ethyl acetate and washed with water (2×100 ml). The organic phase is then dried over MgSO4, filtered and concentrated. The residue is triturated in diisopropylether and pentane and dried under vacuum to yield 2.07 g of 2-mercapto-5-(tert-butyl-dimethyl-silanyloxy)-benzimidazole. Yield=70%. Analytical LC/MS (method B): retention time=4.79 min. m/z=281.36 (positive ion mode).
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