A mixture of 2.14 g (7.09 mmol) rac-(3S,4R)-1-benzyl-4-(4-chlorophenyl)-pyrrolidin-3-amine, 540 uL (9.5 mmol) acetaldehyde, 609 uL (10.6 mmol) acetic acid and 2.25 g (10.6 mmol) sodium triacetoxyborohydride was stirred at 20° C. over night. Water and Na2CO3 aq. was added and the mixture was extracted with ethyl acetate. The combined organic layers were dried with Na2SO4 and evaporated to dryness. The residue was taken up in 60 mL DCM. 1.15 g DIPEA (8.86 mmol) and 43.3 mg DMAP (354 μmol) was added. The brownish solution was cooled with an ice-bath. A solution of 1.48 g (8.51 mmol) 4-fluorophenyl chloroformate in 15 mL DCM was added drop-wise and the mixture was stirred at 0-5° C. for 1 h. Na2CO3 aq. was added and the mixture was extracted with DCM. The combined organic layers were washed with brine, dried with Na2SO4 and evaporated to dryness. The residue was purified by flash column chromatography on silica eluting with a gradient formed from TBDME and heptane to yield after evaporation of the product containing fractions 1.62 g (50%) of the title compound as yellow oil. MS m/e: 453.3 [M+H]+.
