C(=O)([O-])[O-].[K+].[K+].[CH2:7](Br)[C:8]1[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=1.CN(C)C=O.[OH:20][C:21]1[C:22]([CH:31]=[O:32])=[CH:23][C:24]2[O:29][CH2:28][CH2:27][O:26][C:25]=2[CH:30]=1>C(OCC)(=O)C.O>[CH2:7]([O:20][C:21]1[C:22]([CH:31]=[O:32])=[CH:23][C:24]2[O:29][CH2:28][CH2:27][O:26][C:25]=2[CH:30]=1)[C:8]1[CH:13]=[CH:12][CH:11]=[CH:10][CH:9]=1Potassium carbonate (0.27 g) and benzyl bromide (0.17 mL) were sequentially added to an N,N-dimethylformamide (2 mL) solution of 7-hydroxy-2,3-dihydrobenzo[1,4]dioxine-6-carbaldehyde (0.23 g), followed by stirring at 65° C. for 2 hours. Benzyl bromide (0.077 mL) was added to the reaction mixture, followed by stirring at 65° C. for 30 minutes. The reaction mixture was cooled to room temperature, and then water and ethyl acetate were added thereto. The organic layer was separated, washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography [eluent: 75-60% hexane/ethyl acetate] to obtain 0.32 g of 7-(benzyloxy)-2,3-dihydrobenzo[1,4]dioxine-6-carbaldehyde as a light yellow solid.
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