The reaction system was cooled to -78 °C under nitrogen protection and n-butyllithium (BuLi, 1.6 M hexane solution, 8.52 mL, 13.64 mmol) was slowly added to a tetrahydrofuran (THF, 150 mL) solution of diisopropylamine (2.08 mL, 14.9 mmol). after 45 min, N-(3-ethoxy-2,2-difluoro-3-oxo propyl)-N-benzyl-β-alanine ethyl ester (compound W, 2.13 g, 6.2 mmol) to a solution of THF (50 mL). The cooling bath was removed and the reaction mixture was allowed to warm slowly to room temperature and stirred overnight. Upon completion of the reaction, the reaction was quenched by the addition of an aqueous solution of ammonium chloride (NH4Cl, 200 mL) and the organic and aqueous layers were separated. The aqueous phase was extracted with ethyl acetate (EtOAc, 3 x 150 mL). All organic layers were combined, washed with saturated brine and dried over anhydrous sodium sulfate (Na2SO4). After concentration under reduced pressure, the residue was purified by fast column chromatography (FC, eluent: EtOAc/heptane=1:9) to afford ethyl 1-benzyl-5,5-difluoro-4-oxo-piperidine-3-carboxylate (1.5 g, 81% yield).LC-MS analysis: retention time (Rut)=1.04 min, mass spectra (ES+) m/z =298.22.
