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