121.7 g crude (R)-4-(4-benzyloxy-phenyl)-1-(1-phenyl-ethyl)-piperidin-4-ol was dissolved at 40° C. in 1.21 L dichloroethane. 59.4 g (471 mmol) oxalic acid (Merck 492) was added. The mixture was boiled for 3 h, while 20 mL of water was separated. The reaction mixture was washed at room temperature with 1.2 L 10% Na2CO3. The precipitate (52 g) was separated from filtrate A and added to a mixture of 250 mL 2 N NaOH and 300 mL dichloromethane, where it was dissolved after stirring for 30 min at 30-35° C. The organic phase was separated and washed with a half-saturated NaCl solution. The resulting precipitate was separated and dissolved in 200 mL dichloromethane and 60 mL methanol. The combined organic phases were concentrated after drying over Na2SO4. 80 mL ethyl acetate was added to the residue and stirred for 2 h. The crystals were separated, washed with pentane, and dried to yield 36.5 g of (R)-4-(4-benzyloxy-phenyl)-1-(1-phenyl-ethyl)-1,2,3,6-tetrahydropyridine.
