To a stirred mixture of 6-hydroxybenzo[d]oxazole-2-carboxylic acid (0.15 g, 0.86 mmol) in anhydrous N,N-dimethylformamide (2 mL) was added triethylamine (0.10 g, 0.99 mmol), 1-hydroxybenzotriazole hydrate (0.14 g, 0.99 mmol), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (0.20 g, 0.99 mmol), and tert-butyl 4-aminopiperidine-1-carboxylate (0.20 g, 0.99 mmol). The mixture was stirred at room temperature overnight and then concentrated under reduced pressure. The residue obtained was purified by flash chromatography (silica gel, ethyl acetate/hexanes=1/1) to afford tert-butyl 4-(6-hydroxybenzo[d]oxazole-2-carboxamido)piperidine-1-carboxylate as a off-white solid (0.16 g, 52%). 1H-NMR (DMSO-d6, 300 MHz): δ 10.10 (s, 1H), 9.04 (m, 1H), 7.63 (m, 1H), 7.10 (m, 1H), 7.27 (m, 5H), 6.91 (m, 1H), 3.92 (m, 3H), 2.78 (m, 2H), 1.72 (m, 2H), 1.49 (m, 2H), 1.38 (s, 9H); MS (ESI): 362.1 (M+1).
