[F:1][C@:2]1([CH3:18])[C@H:6]([OH:7])[C@@H:5]([CH2:8][OH:9])[O:4][C@H:3]1[N:10]1[CH:17]=[CH:16][C:14](=[O:15])[NH:13][C:11]1=[O:12].[CH3:19][C:20]([Si:23](Cl)([CH3:25])[CH3:24])([CH3:22])[CH3:21].CO.C1(C)C=CC=CC=1>N1C=CC=CC=1>[Si:23]([O:9][CH2:8][C@H:5]1[O:4][C@@H:3]([N:10]2[CH:17]=[CH:16][C:14](=[O:15])[NH:13][C:11]2=[O:12])[C@@:2]([F:1])([CH3:18])[C@@H:6]1[OH:7])([C:20]([CH3:22])([CH3:21])[CH3:19])([CH3:25])[CH3:24]To a stirred solution of 2′-deoxy-2′-fluoro-2′-C-methyluridine (23, 81.1 g, 312 mmol) in dry pyridine (750 mL) was added drop-wise a solution of TBDMSCl (103.19 g, 685.6 mmol) in dry pyridine (500 mL) over a period of 45 min at ambient temperature. The reaction was allowed to stir at ambient temperature for 24 h. Methanol (85 mL) was added to the reaction mixture and it was allowed to stir for 10 min and then the solvents were distilled off under reduced pressure. Hot water (45° C.) (1 L) was added to the reaction mass and the mixture extracted with ethyl acetate (2×500 mL), washed with water (1×500 mL). The organic layer was dried over anhydrous sodium sulfate. Ethyl acetate was distilled off and the residue obtained was co-evaporated with toluene (2×500 mL) to give crude 111 as a white foam. Yield=116.9 g (quantitative).
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