TiCl4(0.2g, 1mmol) and NEt3(0.15 g, 1.5 mmol) were added to toluene, and then add 1-benzyl-4-methyl-3-ketone piperidine (20.3 g, 100 mmol) at 35 ℃. The methylamine solution is added to the reaction solution (9.32 g, 120 mmol) and reaction for 4 h, followed by adding NaBH (OAC) 3 (0.32 g, 1.5 mmol) and glacial acetic acid 2 ml. After the reaction is complete, add saturated salt water to wash the reaction mixture. (3R,4R)-1-benzyl-N,4-dimethylpiperidin-3-amine dihydrochloride was obtained after further purification.