A solution of 1,1-dimethylethyl 4-amino-1-piperidinecarboxylate (11.19 g, 55.9 mmol), 5-chloro-6-methyl-3-pyridinecarbaldehyde (for a synthesis see WO2006/137485 A1 Example 256) (7.82 g, 50.3 mmol) and Na2SO4 (8.73 g, 61.5 mmol) in DCE (200 ml) was stirred at 90° C. for 4.5 h and at room temperature overnight. NaBH(OAc)3 (35.5 g, 168 mmol) was added portionwise for 7 h until imine was not detected by LCMS analysis. 10% NaHCO3 was added and the organic phase was extracted twice with DCM, washed with brine, dried (MgSO4), filtered and concentrated under reduced pressure to give 1,1-dimethylethyl 4-{[(5-chloro-6-methyl-3-pyridinyl)methyl]amino}-1-piperidinecarboxylate (18.7 g, 94%) as a yellow oil.
