To a stirred mixture of 1-benzyl-3-piperidone (72 g) and dimethyl carbonate (500 mL) was added sodium hydride (38 g, 60% oil dispersion) in batches. The reaction mixture was heated to reflux for 20 min and then the reaction was quenched by the slow addition of water (800 mL). The aqueous phase was extracted with ethyl acetate (3 x 400 mL), the organic phases were combined and dried over anhydrous sodium sulfate. The organic phase was concentrated under reduced pressure to give methyl 1-benzyl-3-oxopiperidine-4-carboxylate as a brown oil (93 g, 99% yield). lc-MS (ESI+): m/z 248 [M+H]+.
