To a solution of benzyl (3S*,4R*)-1-(tert-butoxycarbonyl)-4-(ethoxycarbonyl)pyrrolidin-3-ylcarbamate (4.4 g, 11.2 mmol) in 150 mL THF, LiBH4 (0.74 g, 33.6 mmol) was added and the mixture was stirred at 80° C. for 1.5 hours. The mixture was quenched with H2O, extracted with EtOAc, the combined organic extracts were dried with Na2SO4 and evaporated. The residue was re-dissolved in 300 mL CH2Cl2, activated MnO2 (3.86 g, 56 mmol) was added and the mixture was stirred for 24 hours at room temperature. MnO2 was filtered off through Celite, and the filtrate was evaporated giving the title aldehyde.
