A mixture of 4-t-butylbenzoic acid (1.15 g, 6.45 mmol), (R)—N-BOC-3-aminopiperadine (1.00 g, 4.99 mmol), BOP (3.42 g, 7.73 mmol), and N-methylmorpholine (2.5 mL, 22.7 mmol) in DMF (10 mL) was stirred at rt for 2 hr and then heated at 55° C. for 3 hr. It was then diluted with ethyl acetate (150 mL), washed sequentially with water (3×50 mL) and brine (50 mL), and dried over anhydrous MgSO4. Removal of solvent under vacuum provided a crude product of the titled compound, which was used in the next step without further purification.
