To a solution of 3 g (6.9 mmol) of (S)-ethyl 2-((2S,3R)-3-(3-chlorophenyl)-2-(4-chlorophenyl)-6-oxopiperidin-1-yl)butanoate (Example 9, Step A) in 45 mL of Et2O was added lithium tetrahydroborate (0.334 g, 13.81 mmol) at 0° C. After being stirred at 0° C. for 50 min, the reaction was quenched (ice cold 10% citric acid) and extracted (2×EtOAc). The combined organic layers were washed with water and sat. aq. NaCl solution, dried over MgSO4, filtered and the filtrate was concentrated under reduced pressure. Purification by flash chromatography on silica gel (eluent: 30% to 60% EtOAc/Hexanes, gradient elution) provided the title compound.
