[CH2:1]([O:8][CH2:9][CH2:10][O:11][CH2:12][CH2:13][O:14][CH2:15][CH2:16][O:17][CH2:18][CH2:19][O:20][CH2:21][CH2:22]O)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C(Br)(Br)(Br)[Br:25].C1(P(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1>C(Cl)Cl>[Br:25][CH2:22][CH2:21][O:20][CH2:19][CH2:18][O:17][CH2:16][CH2:15][O:14][CH2:13][CH2:12][O:11][CH2:10][CH2:9][O:8][CH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1To a solution of Compound 19 (2.04 g, 6.21 mmol) in methylene chloride (20 ml), a solution of carbon tetrabromide (4.12 g, 12.4 mmol) in methylene chloride (10 ml) was added at room temperature; after cooling with ice, triphenylphosphine (2.51 g, 12.4 mmol) was added. The water bath was removed, and this was followed by stirring at room temperature for 1 hour. After concentration under reduced pressure, the residue obtained was purified by silica gel column chromatography (Yamazen YFLC Gel, eluent (n-hexane:ethyl acetate 2:1-1:1)) to yield Compound 20 (light-yellow oil 2.14 g, 88%).
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