(S)-benzyl 3-(tert-butoxycarbonyl(2-fluoroethyl)amino)pyrrolidine-1-carboxylate → (S)-tert-butyl 2-fluoroethyl(pyrrolidin-3-yl)carbamate

To a suspension of 5% Pd/C (1.4 g, 2.2 mmol) in ethanol (12 mL) was added slowly a solution of (S)-benzyl 3-(tert-butoxycarbonyl(2-fluoroethyl)amino)pyrrolidine-1-carboxylate (2.44 g, 21.6 mmol) in methanol (5 mL). The mixture was evacuated and backfilled with nitrogen and then evacuated and backfilled with hydrogen, then stirred under a hydrogen atmosphere for 2 hours. The suspension was filtered through a pad of Celite and washed with a methanol (50 ml). The filtrate was concentrated under reduced pressure to afford (S)-tert-butyl 2-fluoroethyl(pyrrolidin-3-yl)carbamate. To a solution of (S)-1-(6-chloropyridin-3-yl)-2,2,2-trifluoroethyl trifluoromethanesulfonate (0.97 g, 2.82 mmol) in anhydrous THF (5 mL) was added (S)-tert-butyl 2-fluoroethyl(pyrrolidin-3-yl)carbamate (0.92 g, 3.95 mmol) and K2CO3 (0.59 g, 4.23 mmol). The resulting mixture was heated with stirring at 50° C. for 18 hours. After cooling to ambient temperature the mixture was partitioned between water (12 mL) and ethyl acetate (30 mL). The organic layer was separated, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure and the residue obtained purified by column chromatography (Biotage 25M; 10% ethyl acetate:hexanes) to afford tert-butyl (S)-1-((R)-1-(6-chloropyridin-3-yl)-2,2,2-trifluoroethyl)pyrrolidin-3-yl(2-fluoroethyl)carbamate (0.58 g, 48%).