Br[CH2:2][CH2:3][CH2:4][CH2:5][C:6]([O:8][CH2:9][CH3:10])=[O:7].[Br:11][C:12]1[CH:17]=[CH:16][C:15]([OH:18])=[C:14]([CH:19]=[O:20])[CH:13]=1.C(=O)([O-])[O-].[K+].[K+].O>CN(C=O)C>[Br:11][C:12]1[CH:17]=[CH:16][C:15]([O:18][CH2:2][CH2:3][CH2:4][CH2:5][C:6]([O:8][CH2:9][CH3:10])=[O:7])=[C:14]([CH:19]=[O:20])[CH:13]=1Ethyl 5-bromopentanoate (28.6 g) was added to a suspension of 4-bromo-2-formylphenol (25.0 g) and potassium carbonate (18.9 g) in DMF (100 ml), and the resulting solution was stirred at 50° C. overnight under a nitrogen atmosphere. The solution was allowed to cool. Water was added and the resultant mixture was extracted with ethyl acetate. The organic layer was washed with saturated saline and dried over magnesium sulfate. The solvent was distilled off under reduced pressure to obtain yellow oil of ethyl 5-(4-bromo-2-formylphenoxy)pentanoate (40.9 g). 1H-NMR (200 MHz, CDCl3) δ 1.26 (3H, t, J=7.2 Hz), 1.88 (4H, br), 2.40 (2H, t, J=6.6 Hz), 4.05-4.19 (4H, m), 6.87 (1H, d, J=9.2 Hz), 7.61 (1H, dd, J=8.8, 2.6 Hz), 7.92 (1H, d, J=2.6 Hz), 10.41 (1H, s).
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