Trifluoroacetic acid (5 mL) was added dropwise to a solution of N-(1-Boc-piperidin-3-ylmethyl)-N-phenyl-propionamide 5 (1.21 g, 3.49 mmol) in 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 (5.0 mL) and phenylacetaldehyde (5.3 mL, 2M/in DMF, 5.3 mmol) was added. The mixture was stirred at room temperature for 30 min. NaB(OAc)3H (95%, 1.18 g, 5.3 mmol.) was introduced in one portion, and the mixture was stirred at room temperature overnight. The mixture was quenched with 10 mL of aqueous potassium carbonate (sat.), then extracted with ethyl acetate (3×60 mL). The extracts were combined and washed with aqueous NaHCO3 (sat., 2×10 mL), brine (30 mL), and dried over anhydrous sodium sulfate. After the solvent was removed, the remaining oily residue was purified by a flash column chromatography to give 6. IR (film, cm−1) 3060, 3026, 2934, 2854, 2800, 2765, 1662, 1495, 1452, 1401, 1262, 1203, 1150, 1106, 966, 1033, 775, 749; LRMS 351.
