Reaction Steps
To a solution of (3S,4R)-benzyl 3-hydroxy-4-vinylpyrrolidine-1-carboxylate (5.0 g, 20.2 mmol) in PhCF3 (81 mL, 0.25 M solution) was added N,N-diisopropylethylamine (53 mL, 303 mmol), triethylamine trihydrofluoride (19.8 mL, 121 mmol) and perfluoro-1-butanesulfonyl fluoride (PBSF, 3.6 mL, 20.2 mmol). The resulting mixture was stirred at room temperature. After 60 and 120 minutes, additional perfluoro-1-butanesulfonyl fluoride (3.6 mL, 20.2 mmol) was added. After 18 hours, the reaction mixture was transferred to a separatory funnel and was washed twice with 50 mL of 1.0 N HCl (Caution! lots of heat produced), twice with saturated NaHCO3 aqueous solution, and once with H2O and brine. The organic phase was dried over anhydrous Na2SO4, filtered and concentrated to provide a crude brown oil. The pure (3R,4R)-benzyl 3-fluoro-4-vinylpyrrolidine-1-carboxylate was obtained in 81% yield (4.1 g) as a yellow oil by flash column chromatography (SiO2, 10%-30% EtOAc in hexanes). Rf=0.55 (30% EtOAc in hexanes). 1H NMR (CDCl3, 400 MHz): δ 7.37-7.25 (5H, m), 5.9 (1H, m), 5.24 (2H, m), 5.14 (2H, m), 5.03 (1H, dt, J=52.8, 3.2 Hz), 3.9-3.5 (3H, m), 3.53 (1H, m), 2.83 (1H, m). 13C NMR (CDCl3, 100 MHz): δ 154.7, 154.6, 136.6, 131.89, 131.83, 128.48, 128.02, 127.94, 119.00, 118.94, 95.23, 94.47, 93.42, 92.67, 66.99, 66.94, 53.16, 52.94, 52.83, 52.60, 48.17, 48.02, 47.91, 47.83, 47.2, 47.1. LC/MS (uplc): MH+250.0, 0.93 min.
