To a solution of (2R,4S)-4-(tert-Butyl-diphenyl-silanyloxy)-2-hydroxymethyl-pyrrolidine-1-carboxylic acid [4-(2,2,2-trifluoro-ethoxy)-phenyl]-amide (400 mg, 0.699 mmol) in DCM (5 mL) was added TEA (0.14 mL, 1.048 mmol) followed by mesylchloride (0.07 mL, 1.048 mmol) at 0° C. and stirred at room temperature for 12 h. DCM was added, the organic layer was washed with water and brine, dried over Na2SO4 and concentrated to dryness. 400 mg of the residue was taken up in THF (5 mL), t-BuOK (91 mg, 0.813 mmol) was added and the mixture was stirred for 1 h at room temperature. NH4Cl aq. and DCM was added. The organic layer was washed with water and brine, dried over Na2SO4. The residue was purified through column chromatography over silica (elution with 10% ethyl acetate in hexane) to afford (6S,7aR)-6-(tert-Butyl-diphenyl-silanyloxy)-2-[4-(2,2,2-trifluoro-ethoxy)-phenyl]-hexahydro-pyrrolo[1,2-c]imidazol-3-one as an off white solid.
