The TiCl4(0.2g, 1mmol), NEt3(0.15g, 1 . 5mmol) suspended 200 ml in toluene, then add 1-benzyl-4-methyl-3-ketone piperidine (20.3g, 100mmol), temperature control 35 ??C methylamine solution is added to the reaction solution (9.32g, 120mmol) reaction 4 hours, adding NaBH (OAC) 3 (0.32g, 1 . 5mmol), glacial acetic acid 2 ml, temperature control 35 ??C reaction, thin layer monitoring after the reaction is complete. Adding saturated salt water washing, anhydrous sodium sulfate for drying the organic phase, the organic phase concentrated, with residues 35% hydrochloric acid ethanol re-crystallization, to obtain (3R, 4R)-cis-1-benzyl-4-methyl-3-methylamino-piperidine dihydrochloride 17.2g, yield 85.0%, optical purity 99.0% (HPLC method).
