(Diethylamino)sulfur trifluoride → Benzyl 4-fluoro-3-[(2-methylpropan-2-yl)oxycarbonylamino]piperidine-1-carboxylate

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Reaction Steps

To a solution of (+/−)-benzyl 3-(tert-butoxycarbonylamino)-4-hydroxypiperidine-1-carboxylate (1.0 equiv.) in dichloromethane (0.3 M solution) was added DAST at −78° C. The reaction mixture was slowly warmed up to room temperature for 15 h. After quenched with saturated sodium bicarbonate aqueous solution, ethyl acetate and water were added for work-up. The (+/−)-benzyl 3-(tert-butoxycarbonylamino)-4-fluoropiperidine-1-carboxylate was obtained by silica column chromatography (30% EtOAc in hexanes, 40%). LCMS (m/z): 253.1[(M-Boc)H+]; LC Rt=4.08 min. The enantiomerically pure (3R,4R)-benzyl 3-(tert-butoxycarbonylamino)-4-fluoropiperidine-1-carboxylate and (3S,4S)-benzyl 3-(tert-butoxycarbonylamino)-4-fluoropiperidine-1-carboxylate were resolved by chiral HPLC (for analysis: Rt=9.4 min and 12.6 min respectively; n-heptane:isopropanol=90:10 (v:v), Chiralpak AS 250×4.6 mm at 1 mL/min. For preparative separation, n-heptane:isopropanol=90:10 (v:v), Chiralpak AS 50×500 mm. at 90 mL/min)

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