[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.[Li]CCCC.CCCCCC.[C:25](Cl)(=[O:30])[CH2:26][CH2:27][CH:28]=[CH2:29]>C1COCC1>[CH2:1]([C@H:8]1[CH2:12][O:11][C:10](=[O:13])[N:9]1[C:25](=[O:30])[CH2:26][CH2:27][CH:28]=[CH2:29])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1To a solution (0.49 M) of (4S)-4-benzyl 1,3-oxazolidinone in THF cooled to −78° C. was added dropwise n-BuLi in hexane (2.5 M, 1.1 eq). The resulting solution was stirred at −78° C. for 30 min, then a solution of 4-pentenoyl chloride in THF (4 M, 1.1 eq) was added dropwise. The resulting mixture was stirred at −78° C. for 20 min and then allowed to reach 0° C., where it was stirred for another 40 min. The reaction was quenched by addition of sat. aq. NH4Cl before partitioning between H2O and EtOAc. The layers were separated and the aqueous phase re-extracted with EtOAc. The combined organic extracts were washed with brine, dried over Na2SO4, filtered and concentrated in vacuo. The residue was purified by FC eluting with PE/EtOAc (10:1) to give the product as a colourless oil (72%). (ES+) m/z 260 (M+H)+.
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