A solution of 4.73 g (1 equiv.) of tert-butyl methyl(2-oxoethyl)carbamate in 20 ml of methanol was added at room temperature to a solution of 7 g (1 equiv.) of 4-butyl-N,N-dimethylpiperidine-4-amine bis hydrochloride in 50 ml of methanol, and the resulting reaction mixture was stirred for 50 minutes at room temperature. 3.43 g (2 equiv.) of sodium cyanoborohydride were added in portions to this reaction mixture, and stirring was then carried out for 12 hours at room temperature. The progress of the reaction was monitored by thin-layer chromatography (20% MeOH/CHCl3). When the reaction was complete, the reaction mixture was cooled to 0° C. and adjusted to a pH of ˜5 with acetic acid. 2 g of tert-butyl formylmethyl-methylcarbamate and 1.7 g of sodium cyanoborohydride were then added, and the reaction mixture was stirred for a further 60 minutes at room temperature. Finally, the methanol was distilled off, 100 ml of saturated NaHCO3 solution were added, the resulting mixture was extracted with ethyl acetate (2×200 ml), and the combined organic phases were dried over Na2SO4. After removal of the solvent under reduced pressure, 10.5 g of crude product were obtained in the form of a pale yellow oil.
