Trifluoroacetic acid (0.5 mL) was added dropwise to a solution of N-(1-Boc-piperidin-3-ylmethyl)-N-phenyl-propionamide 5 (31 mg, 0.090 mmol) in 0.5 mL of dry CH2Cl2 at 0° C. (ice-water). The reaction mixture was stirred at room temperature for 30 minutes. TLC showed the reaction was complete. After removal of the solvents, the residue was dried under vacuum for 3 hrs. The crude compound was dissolved in DMF (0.5 mL) and 4-anisaldehyde (16.7 μL, 1.5 eq.) was added. The mixture was stirred at room temperature for 30 min. NaB(OAc)3H (95%, 28.45 mg, 1.5 eq.) was introduced in one portion, and the mixture was shaken at room temperature overnight. The mixture was quenched with 5 mL of aqueous potassium carbonate (sat.), then extracted with ethyl acetate (3×10 mL). The extracts were combined and washed with aqueous NaHCO3 (sat., 2×5 mL), brine (10 mL), and dried over anhydrous sodium sulfate. After the solvent was removed, the remaining oily residue was purified by preparative thin layer chromatography (EtOAc/MeOH, 9:1) to afford N-[1-(4-Methoxybenzyl)-piperidin-3-ylmethyl]-N-phenyl-propionamide 10 as a colorless oil (18.7 mg, 59%). LRMS 366.
