[I:1]I.[CH2:3]([O:5][C:6](=[O:22])[C@H:7]([CH2:11][C:12]1[CH:17]=[CH:16][C:15]([O:18][CH3:19])=[C:14]([O:20][CH3:21])[CH:13]=1)[NH:8][CH:9]=[O:10])[CH3:4]>C(Cl)Cl.FC(F)(F)C([O-])=O.[Ag+]>[CH2:3]([O:5][C:6](=[O:22])[C@H:7]([CH2:11][C:12]1[C:17]([I:1])=[CH:16][C:15]([O:18][CH3:19])=[C:14]([O:20][CH3:21])[CH:13]=1)[NH:8][CH:9]=[O:10])[CH3:4]Iodine (2.1 g, 8.3 mmol) was added to a solution of dimethoxy derivative 2 (2.1 g, 7.5 mmol) and silver trifluoroacetate (2.0 g, 9.1 mmol) in methylene chloride (110 mL) and the reaction mixture was stirred at room temperature for 48 h. The yellow precipitate that formed was filtered and washed with methylene chloride. The combined filtrates were washed with 1M Na2S2O5 (2×75 mL), water (2×75 mL), dried and concentrated under reduced pressure to give a solid residue. Recrystallization of this residue from ethyl acetate and petroleum ether gave a white solid 3 (2.3 g, 75%); m.p. 151°-152° C.
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