[I:1][C:2]1[C:3](=[O:17])[NH:4][C:5](=[O:16])[N:6]([CH:15]=1)[C@@H:7]1[O:14][C@H:11]([CH2:12][OH:13])[C@@H:9]([OH:10])[CH2:8]1.[C:18]([OH:21])(=O)[CH3:19].[C:22](OC(=O)C)(=[O:24])[CH3:23]>CCOCC>[C:22]([O:10][C@@H:9]1[C@@H:11]([CH2:12][O:13][C:18](=[O:21])[CH3:19])[O:14][C@@H:7]([N:6]2[CH:15]=[C:2]([I:1])[C:3](=[O:17])[NH:4][C:5]2=[O:16])[CH2:8]1)(=[O:24])[CH3:23]To 5-iodo-2′-deoxyuridine (2.1) (70.8 g, 200 mmol, 1 eq) in an 500 mL Erlenmeyer flask was added acetic acid (72 g, 68.7 mL, 1200 mmol, 6 eq) and acetic anhydride (51 g, 47.1 mL, 500 mmol, 2.5 eq). In a test tube at 0° C., the catalyst for the reaction was prepared by adding HClO4 (0.5 mL) over acetic anhydride (2 mL). Five drops of the catalyst were added into the Erlenmeyer flask at 0° C. with stirring. The reaction mixture was brought to room temperature and stirred for 4 hours where upon a thick white precipitate formed. The Erlenmeyer flask was filled with ether and stirred vigorously for 30 minutes. The white precipitate was filtered and the white cake was washed with ether (500 mL). The product was dried in the vacuum oven overnight to afford (2.2) (90.1 g, 95%) 1H-NMR (CDCl3) δ (ppm) 9.40 (bs, 1H, exchangeable, NH), 7.78 (s, 1H, H-6), 6.18 (dd, J=8.10 Hz, 1H, H-1′), 5.05 (m, 1H, H-3′), 4.07-4.25 (m, 3H, H-4′, 5′), 2.35 (m, 1H, H-2′b), 1.85-2.12 (m, 7H, 2×CH3, H-2′a)
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