[C:1]([O:5][C:6]([NH:8][C@@H:9]([CH2:17][CH2:18][CH2:19][CH2:20]O)[C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])=[O:7])([CH3:4])([CH3:3])[CH3:2].N1C=CN=C1.C1C=CC(P(C2C=CC=CC=2)C2C=CC=CC=2)=CC=1.[I:46]I>C(Cl)Cl>[C:1]([O:5][C:6]([NH:8][C@@H:9]([CH2:17][CH2:18][CH2:19][CH2:20][I:46])[C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])=[O:7])([CH3:4])([CH3:3])[CH3:2]
A modified procedure described in Tetrahedron 2001, 57, 4759-4766 was followed. To a vigorously stirred solution of alcohol 25 (640 mg, 2.11 mmol), imidazole (359 mg, 5.28 mmol), and PPh3 (1.38 g, 5.28 mmol) in CH2Cl2 (20 mL) was added with I2 (1.07 g, 4.22 mmol) portionwise over 15 minutes. The resulting suspension was stirred for an additional 2 hrs and quenched with saturated Na2S2O3 (10 mL). The phases were separated and the aqueous layer was extracted with additional portions of CH2Cl2. The combined extracts were dried (MgSO4) and evaporated in vacuo. The solid residue was suspended in hexane/EtOAc (10/1 v/v, 15 mL) and the liquid decanted. This operation was performed two more times and the decanted liquid fractions were combined and evaporated in vacuo to give a yellow oil. Purification by flash chromatography (silica gel; hexanes→hexanes/EtOAc, 20/1) gave the title compound 30 (851 mg, 98%) as a clear oil.
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