GENERAL STEPS: Butyl acrylate (80 g, 0.624 mol) and a catalytic amount of NaF (1.57 g, 37.5 mmol) were dissolved in anhydrous toluene (800 mL), degassed three times with nitrogen, and subsequently refluxed for 1 hour. Then, trimethylmethylsilyl difluoro(fluorosulfonyl)acetate (250 g, 0.999 mol) was slowly added dropwise to the refluxed solution over 40 min. After the dropwise addition was completed, the resulting light colorless solution was continued to reflux for 8 hours under nitrogen protection. After completion of the reaction, the reaction solution was cooled to room temperature to obtain a light yellow solution. The solvent was removed by distillation under reduced pressure at about 45°C. The combined residue (~130 mL) was first distilled at 130°C and atmospheric pressure to remove residual toluene, followed by a decompression distillation (~0.02 atm) at the same temperature. Butyl 2,2-difluorocyclopropane carboxylate (65 g, 59% yield) was finally obtained as a colorless oil.1H NMR (400 MHz, CDCl3) δ ppm: 4.09-4.21 (m, 2H), 2.36-2.47 (m, 1H), 2.04-2.07 (m, 1H), 1.60-1.66 (m, 3H), 1.36- 1.42 (m, 2H), 0.94 (t, J = 7.2 Hz, 3H).
