(S)-3-Formylpyrrolidine-1-carboxylic acid t-butyl ester (1.5 g, 7.5 mmol) was dissolved in THF (15.0 mL, 186 mmol). The reaction mixture and cooled at −78° C., before adding allylmagnesium bromide (1.0M in ether; 11.3 mL, 11.3 mmol) dropwise. The resulting mixture was allowed to warm to room temperature slowly overnight. The reaction was quenched with saturated aqueous NH4Cl (30 mL), added dropwise. The resulting mixture was extracted with EtOAc (2×30 mL), then the combined organic layers were washed with saturated aqueous NaHCO3 (1×30 mL) and saturated aqueous NaCl (1×30 mL), then dried over anhydrous MgSO4, filtered, and concentrated in vacuo to yield the crude product, which was then purified by preparative HPLC (10-50% MeCN:H2O; 0.05% TFA; over 80 minutes). Each diastereomer dissolved in EtOAc and free based by adding saturated aqueous NH4CO3. The organics were separated, dried over Na2SO4, and the solvent removed to yield (S)-3-((S)-1-hydroxy-but-3-enyl)pyrrolidine-1-carboxylic acid t-butyl ester (105 mg; 1st eluting peak) and (S)-3-((R)-1-hydroxy-but-3-enyl)pyrrolidine-1-carboxylic acid t-butyl ester (90 mg; 2nd eluting peak).
