[Cl:1][C:2]1[N:10]=[C:9]2[C:5]([NH:6][CH:7]=[N:8]2)=[C:4]([Cl:11])[N:3]=1.[H-].[Na+].[CH3:14][Si:15]([CH2:18][CH2:19][O:20][CH2:21]Cl)([CH3:17])[CH3:16]>CN(C=O)C>[Cl:1][C:2]1[N:10]=[C:9]2[C:5]([N:6]=[CH:7][N:8]2[CH2:21][O:20][CH2:19][CH2:18][Si:15]([CH3:17])([CH3:16])[CH3:14])=[C:4]([Cl:11])[N:3]=1A solution of 2,6-dichloropurine (4.0 g, 21 mmol) in DMF (100 mL) was cooled to 0° C. NaH (1.69 g, 42.3 mmol, 60% dispersion in mineral oil) was added, and the mixture was stirred at rt for 30 min. The reaction was again cooled to 0° C., and SEM-Cl (5.29 g, 31.7 mmol) was added. The reaction was stirred at rt for 1 hr, at which point LCMS showed complete consumption of starting material. Water was added slowly, and the mixture was extracted with EtOAc (three times). The combined organics were washed with water (three times) and brine, dried over Mg2SO4, and filtered. The filtrate was concentrated, and the crude material was purified by flash chromatography on a Biotage 40M column; eluted with 0%-20% EtOAc/heptane to afford the title compound (3.82 g, 57% yield) as a pale yellow oil. 1H NMR (400 MHz, chloroform-d) δ ppm 8.26 (s, 1H) 5.64 (s, 2H) 3.61-3.67 (m, 2H) 0.92-1.00 (m, 2H) −0.01 (s, 9H).
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