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A mixed solution of acetic acid (6.2 mL) and acetic anhydride (6.2 mL) containing 6-methoxy-2,2-dimethyl-2H-1-benzopyran (3.1 g, 16.4 mmol) was cooled with ice, nitric acid (1.37 mL, 18.0 mmol) was added dropwise and then the mixture was stirred at 0° C. for 1 hour. Upon the completion of the reaction, an aqueous solution of 1 mol/L sodium hydroxide was added to the reaction solution, the resulting solution was extracted with ethyl acetate (150 mL). The organic phase was washed twice with 1 mol/L sodium hydroxide aqueous solution and once with saturated sodium chloride solution. Then, the organic phase was dried over anhydrous magnesium sulfate. After distilling off the solvent, the residue was purified by column chromatography (hexane/ethyl acetate=6/1) and the aimed product was obtained as yellow crystal (yield: 79%).

1. additionwas added dropwise
2. customUpon the completion of the reaction
3. extractionthe resulting solution was extracted with ethyl acetate (150 mL)
4. washThe organic phase was washed twice with 1 mol/L sodium hydroxide aqueous solution and once with saturated sodium chloride solution
5. dry with materialThen, the organic phase was dried over anhydrous magnesium sulfate
6. distillationAfter distilling off the solvent
7. customthe residue was purified by column chromatography (hexane/ethyl acetate=6/1)