Trifluoroacetic acid → (2R,5R)-2-[(R)-{[tert-butyl(dimethyl)silyl]oxy}(phenyl)methyl]-5-(4-nitrobenzyl)pyrrolidine

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Reaction Steps

To a solution of MOZ protected ketone amine (from Step G, 34 g, 56 mmol) in DCM (350 ml) was added TFA (256 ml) and the resulting mixture stirred at room temperature for 1.5 h. The solution was evaporated under vacuum and residue partitioned between DCM and sat. NaHCO3. The organic layer was dried over MgSO4, filtered and evaported. The residue was dissolved in MeOH (750 ml) and cooled to 0° C. via ice/water bath. Sodium cyanoborohydride (21.2 g, 337 mmol) was then added and the resulting mixture was stirred overnight to allow to warm to room temperature. The mixture was quenched by addition of water and the organics removed under vacuum. The aqueous layer was then extracted with EtOAc (×2) and the combined EtOAc layers washed with sat. NaCl, dried over MgSO4, filtered and evaporated under vacuum. The residue was purified by column chromatography on silica (eluent: gradient rising from 100% Hexanes to 35% EtOAc in Hexanes) to give 16.4 g (63.4%) of the first isomer, (2R,5S)-2-[(R)-{[tert-butyl(dimethyl)silyl]oxy}(phenyl)methyl]-5-(4-nitrobenzyl)pyrrolidine, and 3.1 g (12%) of the second isomer (2R,5R)-2-[(R)-{[tert-butyl(dimethyl)silyl]oxy}(phenyl)methyl]-5-(4-nitrobenzyl)pyrrolidine.

Provenance & Evidence