To a solution of (R)-tert-butyl 3-aminopiperidine-1-carboxylate (8) (6.27 g, 33.5 mmol) in DCM (100 mL) was added DIEA (8.75 mL, 50.3 mmol) and then 4-tert-butylbenzoyl chloride (8.0 mL, 43.6 mmol) in drop-wise manner. The mixture was stirred for 3 h at RT, diluted with DCM, washed with 1N NaOH, dried, and concentrated. The residue was subjected to flash column chromatography with 0 to 10% EtOAc in DCM to give (R)-tert-butyl 3-(4-tert-butylbenzamido)piperidine-1-carboxylate (11.0 g, 91%). To a solution of (R)-tert-butyl 3-(4-tert-butylbenzamido)piperidine-1-carboxylate (850 mg, 2.36 mmol) in DMF (10 mL) was added NaH (60% in mineral oil, 190 mg, 4.72 mmol). The mixture was stirred at RT for 10 min and then iodomethane (0.44 mL, 7.08 mmol) was added. The mixture was stirred at RT for 1 h, and diluted with 150 mL EtOAc. The mixture was washed with water ×2, dried, and concentrated. The residue was subjected to flash column with 0 to 3% MeOH in DCM to afford (R)-tert-butyl 3-(4-tert-butyl-N-methylbenzamido)piperidine-1-carboxylate (9) in quantitative yield. It was treated with 15 mL 4N HCl in dioxane at RT for 1 h. The mixture was concentrated in vacuo to dryness to afford (R)-4-tert-butyl-N-methyl-N-(piperidin-3-yl)benzamide (10) HCl salt in quantitative yield.
