Tert-butyl-4-(methoxy(methyl)carbamoyl)piperidine-1-carboxylate (2.29 g, 8.32 mmol) was dissolved in 30 ml of tetrahydrofuran (THF), and the resulting solution was cooled to -78 °C. To the solution, methylmagnesium bromide (3.0 M) (7.73 ml, 10.82 mmol) was slowly added, and the solution was stirred at 0 °C for 1 hr. After the reaction was completed with a 2 N hydrochloric acid aqueous solution, 6 N sodium hydroxide solution was added to adjust the pH to 10. Then the solution was extracted with dichloromethane. The organic layer was treated with magnesium sulfate (MgSO4) and filtered, and the solution was concentrated. The resulting residue was isolated and purified by silica gel column chromatography (dichloromethane/methanol = 10/1) to give 4-Acetyl-piperidine-1-carboxylic acid tert-butyl ester (6.36 g, 94.0 percent).
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