The general procedure for the synthesis of benzyl ethyl 4-oxo-piperidine-1,3-dicarboxylate from benzyl chloroformate is as follows: a mixture of 1-benzyl-3-ethoxy-4-piperidone hydrochloride (89.0 g, 298.9 mmol) and palladium hydroxide (4.2 g, 5.9 mmol) in methanol (700 mL) was degassed and subjected to 40 psi hydrogen pressure by The reaction was shaken overnight. Upon completion of the reaction, the mixture was filtered through a diatomaceous earth pad and the filtrate was concentrated. The resulting solid was dissolved in dichloromethane (800 mL) and triethylamine (90.7 g, 897 mmol) was added. After cooling the solution to 0 °C, benzyl chloroformate (56.1 g, 329 mmol) was slowly added. The reaction mixture was stirred at 25 °C for 15 h. The reaction was subsequently quenched with water (500 mL). The aqueous layer was extracted with dichloromethane (2 x 400 mL), the organic layers were combined and dried over anhydrous magnesium sulfate and concentrated to give the crude product. The crude product was purified by silica gel column chromatography (eluent ratio of petroleum ether: ethyl acetate = 5:1) to afford benzyl ethyl 4-oxo-piperidine-1,3-dicarboxylate (72 g, 78% yield), which could be used for subsequent reactions without further purification.
