[Cr](Cl)([O-])(=O)=O.[NH+]1C=CC=CC=1.C([O-])(=O)C.[Na+].[OH:17][CH2:18][CH2:19][CH2:20][CH2:21][C:22]1[CH:31]=[CH:30][C:25]([C:26]([O:28][CH3:29])=[O:27])=[CH:24][CH:23]=1>C(Cl)Cl.C(OCC)C>[CH3:29][O:28][C:26]([C:25]1[CH:30]=[CH:31][C:22]([CH2:21][CH2:20][CH2:19][CH:18]=[O:17])=[CH:23][CH:24]=1)=[O:27]To a mixture of 4.97 g (23 mmol) of pyridinium chlorochromate and 1.23 g (15 mmol) of sodium acetate in 100 mL of dry methylene chloride was added 3.2 g (15.3 mmol) of methyl 4-(4-hydroxybutyl)benzoate in 50 mL of methylene chloride at room temperature. The resulting mixture was stirred at room temperature for 3 hours, diluted with 150 mL of ethyl ether, filtered through a silica gel pad, and concentrated. The residue was purified by column chromatography (silica gel/hexane:ethyl acetate=4:1) to give 2.85 g (90%) of 4-(4-methoxycarbonylphenyl)butyraldehyde as a light yellow oil: 1H NMR (CDCl3) δ 2.15-2.40 (2H, m), 2.72 (2H, t, J=6.6 Hz), 2.96 (2H, t, J=7.2 Hz), 4.15 (3H, s), 7.50 (2H, d, J=8.1 Hz), 8.21 (2H, d, J=8.1 Hz), 10.01 (1H. s); MS m/z 206 (M+), 175, 162, 131,103, 91, 63.
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