A solution of (S)-2-((3S,5R,6S)-3-allyl-5-(3-chlorophenyl)-6-(4-chlorophenyl)-2-oxopiperidin-1-yl)butanal (80 mg, 0.186 mmol) and trimethyl(trifluoromethyl)silane (82 μL, 0.558 mmol) in THF (929 μL) was treated at 0° C. with 1 M tetrabutylammonium fluoride in THF (93 μL, 0.093 mmol). After being stirred for 1 h, three additional equivalents of trimethyl(trifluoromethyl)silane (82 μL, 0.558 mmol) and 1 M tetrabutylammonium fluoride in THF (93 μL, 0.093 mmol) were added to the reaction at 0° C. and the reaction was stirred for 14 h. The reaction mixture was diluted (EtOAc), washed (1×H2O and 1×sat. aq. NaCl solution), dried (Na2SO4), and concentrated under reduced pressure. Purification by reverse phase preparatory HPLC (Gemini™ Prep C18 5 μm column, Phenomenex, Torrance, Calif.; eluent: 60 to 90% acetonitrile+0.1% TFA in water+0.1% TFA, gradient elution) provided two compounds which are diastereomers at the secondary alcohol.
