[CH2:1]([C@H:8]1[CH2:12][O:11][C:10](=[O:13])[N:9]1[C:14](=[O:22])[CH2:15][C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C[Si]([N-][Si](C)(C)C)(C)C.[Na+].[CH2:33](I)[CH:34]=[CH2:35].[Cl-].[NH4+]>C(OCC)(=O)C.CCCCCC.O1CCCC1>[CH2:1]([C@H:8]1[CH2:12][O:11][C:10](=[O:13])[N:9]1[C:14](=[O:22])[CH:15]([C:16]1[CH:17]=[CH:18][CH:19]=[CH:20][CH:21]=1)[CH2:35][CH:34]=[CH2:33])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1Combine (S)-4-benzyl-3-phenylacetyl-2-oxazolidinone (14.13 g, 47.9 mmol) and tetrahydrofuran (150 mL). Cool in a dry-ice/acetone bath. Add dropwise a solution of sodium bis(trimethylsilyl)amide (52.6 mL, 1.0 M in tetrahydrofuran, 52.6 mmol). After 25 minutes, add allyl iodide (13.12 mL, 143.5 mmol) and then replace the bath with a dry-ice/carbon tetrachloride bath. After 1 hour, quench the reaction by the addition of a saturated aqueous ammonium chloride solution, extract with diethyl ether, and separate the layers. Dry the organic layer over Na2SO4, filter, and evaporate in vacuo to give a residue. Chromatograph the residue on silica gel eluting with 15% ethyl acetate/hexane. Combine the product containing fractions, evaporate, and recrytallize from chloroform/hexane to give (S)-4-benzyl-3-(2-phenylpent-4-enoyl)-2-oxazolidinone: Rf=0.40 (silica gel, 15% ethyl acetate/hexane).
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