1217190-38-9

140927-13-5

Benzyl 5-hydroxy-2-azabicyclo[2.2.1]heptane-2-carboxylate (Intermediate I-41, 9.7 g, 39 mmol, 1.0 eq.) was used as a starting material, which was dissolved in acetone (400 mL) and the solution was cooled to 0°C. Jones reagent (18 mL, 47 mmol, 1.2 equiv) [which was prepared from chromium trioxide (26.7 g), concentrated sulfuric acid (27.3 mL) and water (80 mL)] was added slowly and dropwise with stirring. The reaction mixture was stirred continuously for 3 hours at 0°C. Upon completion of the reaction, the excess chromic acid was quenched by dropwise addition of isopropanol (propan-2-ol). Subsequently, the reaction solution was alkalized with 3.0 M aqueous sodium hydroxide and the solvent was removed by rotary evaporation. The residue was dissolved in water and the crude product was extracted with dichloromethane. The organic layers were combined and dried with anhydrous magnesium sulfate (MgSO4), and after filtration to remove the desiccant, the filtrate was concentrated under reduced pressure to obtain the crude product. Finally, the crude product was purified by silica gel column chromatography to afford the target compound benzyl 5-oxo-2-azabicyclo[2,2,1]heptane-2-carboxylate (Intermediate I-42, 7.6 g, 80% yield). Mass spectrometric (ESI) analysis showed m/z 246 (M + H+).