General procedure for the synthesis of ethyl (2R,4R)-4-methyl-2-piperidinecarboxylate from the compound (CAS: 198641-56-4): (1'S,2R,4R)-6 (2.5 g, 9 mmol) was dissolved in ethanol (120 mL) and 10% Pd(OH)2/C (0.27 g) was added. The hydrogenation reaction was carried out at room temperature and at atmospheric pressure. The reaction progress was monitored by TLC (unfolding agent: chloroform/methanol, 9:1). After 4 hours of reaction, the catalyst was removed by filtration through a diatomaceous earth pad. The filtrate was concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (silica gel to sample mass ratio 1:20) to afford pure ethyl (2R,4R)-4-methyl-2-piperidinecarboxylate (0.7 g, 45% yield) using dichloromethane/methanol (98:2) as eluent. The product was characterized by 1H NMR (CDCl3): δ 0.96 (d, 3H, J = 6.50 Hz, CH3-4); 1.15 (m, 1H, H-5a); 1.32 (t, 3H, J = 7.2 Hz, CH3CH2); 1.42-1.54 (m, 1H, H-3); 1.5-1.69 (m, 2H, H-4, H-5b) ; 2.00-2.11 (m, 2H, H-3b and NH); 2.87 (m, 2H, H-6); 3.65 (m, 1H, H-2); 4.21 (q, 2H, J = 7.2 Hz, CH2CH3). Specific optical rotation [α]20D = -22 (c 5, ethanol) (enantiomeric excess value e.e. = +24).
![2-Piperidinecarboxylic acid, 4-methyl-1-[(1S)-1-phenylethyl]-, ethyl ester, (2R,4R)-](/CAS/20210305/GIF/198641-56-4.gif)
