[CH3:1][O:2][C:3](=[O:27])[CH:4]([C:16]1[CH:21]=[CH:20][C:19]([S:22]([CH3:25])(=[O:24])=[O:23])=[C:18]([Cl:26])[CH:17]=1)[CH2:5][CH:6]1[CH2:10][CH2:9][C:8]2(OCCC[O:11]2)[CH2:7]1.Cl>O1CCCC1>[CH3:1][O:2][C:3](=[O:27])[CH:4]([C:16]1[CH:21]=[CH:20][C:19]([S:22]([CH3:25])(=[O:24])=[O:23])=[C:18]([Cl:26])[CH:17]=1)[CH2:5][CH:6]1[CH2:10][CH2:9][C:8](=[O:11])[CH2:7]1A solution of 2-(3-chloro-4-methanesulfonyl-phenyl)-3-(6,10-dioxa-spiro[4.5]dec-2-yl)-propionic acid methyl ester (1.21 g, 2.90 mmol) in tetrahydrofuran (14.5 mL) was treated with a 5% aqueous hydrochloric acid solution (6.4 mL) and stirred at 25° C. for 29 h. The reaction was then concentrated in vacuo to remove tetrahydrofuran. The resulting aqueous residue was diluted with water (200 mL) and extracted with ethyl acetate (2×100 mL). The combined organic layers were dried over sodium sulfate, filtered, and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 70–230 mesh, 50% ethyl acetate/hexanes) afforded 2-(3-chloro-4-methanesulfonyl-phenyl)-3-(3-oxo-cyclopentyl)-propionic acid methyl ester (1.03 g, 99%) as a colorless oil: EI-HRMS m/e calcd for C16H19ClO5S (M)+ 358.0642 found 358.0630.
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