(-)-alpha-Methoxy-alpha-(trifluoromethyl)phenylacetyl chloride → 1,1-dimethylethyl (2R)-2-(1-{[(phenylmethyl)oxy]carbonyl}-3-{[(2R)-3,3,3-trifluoro-2-(methyloxy)-2-phenylpropanoyl]oxy}azetidin-3-yl)piperidine-1-carboxylate

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To a solution of 1,1-dimethylethyl 2-(3-hydroxy-1-{[(phenylmethyl)oxy]carbonyl}azetidin-3-yl)piperidine-1-carboxylate (368 mg, 0.94 mmol), prepared using procedures similar to those described in Reference 5, in dichloromethane (5 mL) was added DMAP (115 mg, 0.94 mmol) and the resulting solution was cooled to 0° C. (R)-(−)-α-Methoxy-α-trifluoromethylphenylacetyl chloride (105 μL, 0.56 mmol) was added to the solution by syringe and the mixture was allowed to warm to room temperature then stirred an additional 12 hours. The solution was then partitioned with saturated aqueous sodium bicarbonate and the organic phase dried over anhydrous magnesium sulfate then filtered and concentrated to an oily residue. Silica gel flash chromatography using hexanes:ethyl acetate 3:1 as eluent afforded the less polar 1,1-dimethylethyl (2R)-2-(1-{[(phenylmethyl)oxy]carbonyl}-3-{[(2R)-3,3,3-trifluoro-2-(methyloxy)-2-phenylpropanoyl]oxy}azetidin-3-yl)piperidine-1-carboxylate (27.5 mg, 5% yield), the more polar 1,1-dimethylethyl (2S)-2-(1-{[(phenylmethyl)oxy]carbonyl}-3-{[(2R)-3,3,3-trifluoro-2-(methyloxy)-2-phenylpropanoyl]oxy}azetidin-3-yl)piperidine-1-carboxylate (105 mg, 19% yield) and starting material (253 mg, 69% recovery).

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