[BH4-].[Na+].[CH3:3][O:4][C:5]([C@@H:7]1[CH2:11][C:10](=[O:12])[CH2:9][C@@H:8]1[C:13]([O:15][CH3:16])=[O:14])=[O:6]>CO>[CH3:16][O:15][C:13]([CH:8]1[CH2:9][CH:10]([OH:12])[CH2:11][CH:7]1[C:5]([O:4][CH3:3])=[O:6])=[O:14]Sodium borohydride (1.11 g, 0.029 mol) was added to a stirred solution of (1R,2S)-4-oxo-cyclopentane1,2-dicarboxylic acid dimethyl ester (4.88 g, 0.0244 mol) in methanol (300 mL) at 0° C. After 1 h the reaction was quenched with 90 ml brine, concentrated and extracted with ethyl acetate. The organic phases were pooled, dried, filtered and concentrated. The crude product was purified by flash column chromatography (toluene/ethyl acetate 1:1) which gave the title compound (3.73 g, 76%) as a yellow oil.
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