288154-16-5

501-53-1

183673-68-9

288154-16-5

To a solution of compound 2-c (0.50 g, 2.05 mmol) in tetrahydrofuran (THF, 4 mL) was added an aqueous sodium hydroxide solution (0.17 g, 4.30 mmol, 2.10 equiv, 4 mL). The reaction mixture was cooled to 0°C. Benzyl chloroformate (0.32 mL, 2.25 mmol, 1.10 eq.) was slowly added dropwise followed by stirring at room temperature for 24 hours. Upon completion of the reaction, the reaction mixture was washed with ether, then the pH of the aqueous layer was adjusted to 2.5 with 1N hydrochloric acid and extracted with ethyl acetate. The organic layers were combined, dried with anhydrous magnesium sulfate, and concentrated under reduced pressure to afford 4-benzyloxycarbonylaminopiperidine-1,4-dicarboxylic acid mono-tert-butyl ester as a white solid (0.55 g, 71% yield), which was used directly in the next step of the reaction.1H-NMR (CDCl3) δ: 7.29-7.39 (m, 5H), 5.10 (s, 2H), 3.84 (bs, 2H). 3.05-3.15 (m, 2H), 1.95-2.12 (m, 4H), 1.45 (s, 9H).