[CH2:1]([C@H:8]1[CH2:12][O:11][C:10](=[O:13])[NH:9]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([Li])CCC.[C:19]1([CH2:25][CH2:26][CH2:27][CH2:28][C:29](Cl)=[O:30])[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1.OS([O-])(=O)=O.[K+]>C1COCC1>[CH2:1]([C@H:8]1[CH2:12][O:11][C:10](=[O:13])[N:9]1[C:29](=[O:30])[CH2:28][CH2:27][CH2:26][CH2:25][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1To a stirring solution consisting of (S)-4-benzyloxazolidin-2-one (0.9 g, 5.08 mmol) in THF (20 mL) at −78° C. was slowly added n-butyllithium solution (3.5 mL, 5.6 mmol, 1.6 M solution in hexane). The reaction mixture was stirred at −78° C. for two hours, after which time 5-phenylpentanoyl chloride (1 g, 5 mmol, prepared by treatment of 5-phenylpentanoic acid with oxalyl chloride and catalytic DMF) was slowly added. The reaction mixture was stirred at −78° C. for two hours and was then allowed to rise to room temperature overnight. The reaction mixture was acidified with 5% KHSO4 and extracted twice with ethyl acetate. The organic phase was washed with brine, dried over sodium sulfate, filtered, and concentrated under vacuum. The residue was purified by silica gel chromatography. Elution with ethyl acetate-heptane (25:75 v/v) afforded the title compound (1.4 g, 82%) as a clear oil; TLC Rf 0.40 (solvent system: 25:75 v/v ethyl acetate-heptane); MS (ESI+) m/z 337.4 (M+H)+, 360.2 (M+Na)+.
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