Dichloromethane → 1-(4-Chloro-3,5-dimethoxyphenyl)ethanone

To a solution of the compound obtained in the above (1) (1.23 g) in dichloromethane 928 mL) was added 85% activated manganese dioxide (5.81 g), and the mixture was stirred at 40° C. for 4 hours. The reaction solution was cooled to room temperature, and then thereto was added water-chloroform, and an insoluble was filtered off through Celite, and then the organic layer was separated. The organic layer was concentrated under reduced pressure, and the resulting residue was purified by silica gel column chromatography (eluent: n-hexane/ethyl acetate=10/1→1/1) to give 1-(4-chloro-3,5-dimethoxyphenyl)ethanone [REx(22-2)] (723 mg) as a colorless powder.