1. A Parr autoclave was charged with ethyl 1-benzyl-3-oxopiperidine-4-carboxylate hydrochloride (10.0 g, 33.58 mmol), 10% Pd/C catalyst (1.0 g), di-tert-butyl dicarbonate (Boc2O, 14.64 g, 67.16 mmol), sodium carbonate (Na2CO3, 3.56 g, 33.58 mmol) and anhydrous ethanol (EtOH, 100 ml).
2. Hydrogen was introduced into the autoclave to a pressure of 38 bar and the reaction mixture was subsequently stirred at 50 °C for 48 h. After the reaction was completed, the reaction mixture was purified by boiling the hydrogen gas under high pressure.
3. After completion of the reaction, the autoclave was cooled to 25 °C and the hydrogen pressure was slowly released.
4. The catalyst was removed by filtration and the filtrate was concentrated under reduced pressure to give a yellow oil.
5. The crude product was purified by column chromatography (eluent: hexane/ethyl acetate, 2:1) to afford ethyl 1-N-Boc-3-oxopiperidine-4-carboxylate (9.10 g, 100% yield) as a clear oil. 6. The product was subjected to thin layer chromatography (TLC).
6. The product was detected by thin layer chromatography (TLC) with an Rf value of 0.70 (Expanding agent: hexane/ethyl acetate, 2:1).
7. The structure of the product was confirmed by 1H NMR (CDCl3, 400 MHz) and HRMS (CI) and the results were as expected.
