Di-tert-butyl dicarbonate (1.19 g, 5.44 mmol) was slowly added to a solution of 1-benzyl-3,3-difluoropiperidin-4-one (995 mg, 4.42 mmol) dissolved in anhydrous ethanol (60 mL) under nitrogen protection. Subsequently, 20% palladium hydroxide/carbon catalyst (148 mg, 1.05 mmol) was added, and the reaction system was evacuated and displaced three times with hydrogen. The reaction mixture was stirred at room temperature and under hydrogen atmosphere for 20 hours. After completion of the reaction, residual hydrogen was removed and the reaction mixture was filtered through diatomaceous earth (Celite) and the filter cake was washed well with anhydrous ethanol. After purification, the target product tert-butyl 3,3-difluoro-4-oxopiperidine-1-carboxylate (810 mg, 3.44 mmol, 78% yield) was obtained as a white solid.1H NMR (400 MHz, DMSO-d6): δ 3.66-3.52 (m, 2H), 3.39-3.33 (m, 2H), 1.69-1.64 (m, 2H) , 1.38 (s, 9H).
