Ethanol → (3R,4R)-Benzyl 4-((tert-butoxycarbonyl)amino)-3-hydroxypiperidine-1-carboxylate

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Reaction Steps

A solution of (+/−)benzyl 7-oxa-3-azabicyclo[4.1.0]heptane-3-carboxylate (1.0 equiv.) in saturated ammonium hydroxide aqueous solution and ethanol (1:1, 0.05 M solution) in a sealed steel bomb was heated to 70° C. for 5 h. After all volatile materials were removed by N2 gas stream, ethyl acetate and water were added for work-up. The crude regioisomeric mixture, benzyl 3-amino-4-hydroxypiperidine-1-carboxylate and benzyl 4-amino-3-hydroxypiperidine-1-carboxylate was reacted with Boc2O (1.0 equiv.) and triethylamine (1.0 equiv.) in dichloromethane (0.1 M solution). After stirred for 2 h at room temperature, the reaction mixture was extracted with dichloromethane. The polar (+/−)-benzyl 3-(tert-butoxycarbonylamino)-4-hydroxypiperidine-1-carboxylate and nonpolar (+/−)-benzyl 4-(tert-butoxycarbonylamino)-3-hydroxypiperidine-1-carboxylate were obtained by flash column chromatography (20% to 40% EtOAc in hexanes, 28%, 51% each). LCMS (m/z): 351.1 (MH+), Rt=0.81 min, LCMS (m/z): 351.1 (MH+), Rt=0.83 min. The enantiomerically pure (3S,4S)-benzyl 3-(tert-butoxycarbonylamino)-4-hydroxypiperidine-1-carboxylate and (3R,4R)-benzyl 3-(tert-butoxycarbonylamino)-4-hydroxypiperidine-1-carboxylate were resolved by chiral HPLC (For analysis Rt=6.8 min and 9.1 min respectively; n-heptane:ethanol=70:30 (v:v), Chiralpak AD-H prep 250×4.6 mm at 1 mL/min. For preparative separation, n-heptane:ethanol=80:20 (v:v), Chiralpak AS 50×500 mm. at 90 mL/min).

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