[OH:1][C:2]1[CH:3]=[C:4]([CH:7]=[CH:8][C:9]=1[OH:10])[CH:5]=[O:6].C(=O)([O-])[O-].[Na+].[Na+].[CH3:17][O:18][CH2:19][CH2:20]Br.Cl>CN(C)C=O.O.C(OCC)(=O)C>[OH:1][C:2]1[CH:3]=[C:4]([CH:7]=[CH:8][C:9]=1[O:10][CH2:20][CH2:19][O:18][CH3:17])[CH:5]=[O:6]
Commercially available 3,4-dihydroxybenzaldehyde (39.3 g, 285 mmol) and sodium carbonate (45.2 g, 427 mmol) were dissolved in N,N-dimethylformamide (400 mL), then commercially available 2-bromoethyl methyl ether (26.7 mL, 285 mmol) was added under nitrogen atmosphere at room temperature, and the mixture was stirred for 5 days. The mixture was cooled to 0° C. and then 2 M hydrochloric acid, ethyl acetate, and water were added for partition. The aqueous layer was extracted with ethyl acetate, then the combined organic layer was washed with a saturated saline solution and dried over anhydrous magnesium sulfate, and then filtered. The solvent was evaporated, dichloromethane was added, the precipitate was separated by filtration, and then the resultant filtrate was purified with silica gel column chromatography (n-heptane:ethyl acetate=17:3-1:1). The target fraction was concentrated under vacuum to obtain the title compound (12.9 g, 23%).
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