Dimethylformamide → 5,6-Difluoro-1-indanone

Oxalyl chloride (1.12 mL) and DMF (78.2 mg) were added to a solution of 3,4-difluorohydrocinnamic acid (2.00 g) in dichloromethane (3.0 mL) at 0° C., and the reaction solution was stirred at room temperature overnight. After confirming that the raw materials disappeared, the reaction solution was concentrated under reduced pressure. Next, a solution of the resulting residue in dichloromethane (10 mL) was added to a solution of aluminum chloride (2.13 g) in dichloromethane (20 mL) at −30° C. The reaction solution was stirred at room temperature for 1.5 hours. After confirming that the raw materials disappeared, the reaction solution was poured into ice water. The solution was extracted with ethyl acetate. The organic layer was washed with brine, and then dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The resulting residue was purified by silica gel chromatography (elution solvent: heptane-ethyl acetate system) to obtain 535 mg of the title compound. The physical properties of the compound are as follows.