Tert-butyl (R)-2-methyl-4-oxopiperidine-1-carboxylate and 1-N-Boc-2(S)-methyl-piperidin-4-one were synthesized by chiral chromatographic separation using 1-Boc-2-methyl-piperidone as starting material. The procedure was as follows: using a CHIRALPAK ADTM column (size: 4.6×250 mm) with anhydrous ethanol as the mobile phase, the flow rate was set at 1.0 mL/min, and the elution was carried out at the UV detection wavelength of 220 nm. The racemic tert-butyl 2-methyl-4-oxopiperidine-1-carboxylate (15.0 g) was separated to finally obtain isomer 1 ((R)-tert-butyl 2-methyl-4-oxopiperidine-1-carboxylate, 5.28 g, 35% yield) and isomer 2 (1-N-Boc-2(S)-methyl-piperidin-4-one, 5.01 g, 33% yield). The 1H NMR (CDCl3) data of the two isomers were in agreement as follows: δ 4.7 (m, 1H), 4.2 (m, 1H), 3.3 (m, 1H), 2.7 (m, 1H), 2.5 (m, 1H), 2.3 (m, 1H), 2.2 (m, 1H), 1.5 (s, 9H), 1.2 (d, 3H).
