[C:1]([Si:5]([CH3:8])([CH3:7])Cl)([CH3:4])([CH3:3])[CH3:2].[I:9][CH2:10][C@H:11]1[NH:14][C:13](=[O:15])[CH2:12]1.C(N(CC)CC)C>CN(C)C=O>[Si:5]([N:14]1[C@H:11]([CH2:10][I:9])[CH2:12][C:13]1=[O:15])([C:1]([CH3:4])([CH3:3])[CH3:2])([CH3:8])[CH3:7]t-butyldimethylchlorosilane (7.51 g, 49.8 mmol) is added in one portion to an ice-cold, stirring solution of (4S)-4-iodomethyl-azetidin-2-one (10.0 g, 47.4 mmol) and triethylamine (5.04 g, 49.8 mmol) in anhydrous dimethylformamide (100 ml). A voluminous white precipitate forms almost immediately. The reaction mixture is stirred at 0°-5° for 1 hour and then allowed to warm to room temperature. Most of the solvent is removed under vacuum to give a residue which is partitioned between diethyl ether (250 ml) and water. The ethereal phase is washed with 2.5 N hydrochloride acid (50 ml), water (3×50 ml), and brine, dried with magnesium sulfate, filtered, and evaporated under vacuum to provide (4S)-1-(t-butyldimethylsilyl)-4-iodomethyl-azetidin-2-one (15.1 g) as a white solid. Recrystallization from petroleum ether-ethyl ether gives the product as colorless plates, mp 71°-72°; n.m.r. (CDCl3), δ3.8(m,l), δ2.6-3.6 (2 overlapping d of AB, 4) δ1.0 (S,9), δ0.3(S,6), δ0.25(S,6).
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