[OH-].[Na+].[CH3:3][O:4][C:5]1[CH:10]=[CH:9][C:8]([CH2:11][CH2:12][CH2:13][C:14](=[O:18])[C:15]([OH:17])=[O:16])=[CH:7][CH:6]=1.[BH4-].[Na+].Cl>O>[OH:18][CH:14]([CH2:13][CH2:12][CH2:11][C:8]1[CH:7]=[CH:6][C:5]([O:4][CH3:3])=[CH:10][CH:9]=1)[C:15]([OH:17])=[O:16]Sodium hydroxide (24.0 g) and water (450 ml) were added to 5-(4-methoxyphenyl)-2-oxopentanoic acid (66.6 g) (the compound of Reference Example 2), and the resulting mixture was ice-cooled. When to this slurry was added sodium tetrahydroborate (3.99 g) in portions, the reaction mixture once became clear. After the reaction mixture was stirred for 2 hours, a 3N aqueous hydrochloric acid solution (300 ml) was added thereto, followed by extraction with ethyl acetate (300 ml×twice). The organic layer was washed with water (100 ml×three times) and dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure to obtain 2-hydroxy-5-(4-methoxyphenyl)pentanoic acid (63.4 g) as a crude product.
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