To a solution of 4-(5-amino-benzooxazol-2-ylamino)-piperidine-1-carboxylic acid tert-butyl ester (1.40 g, 4.21 mmol, 1.0 equiv) in anhydrous DMF (5 mL) was added cyclobutanecarbonyl chloride (0.55 g, 4.63 mmol, 1.1 equiv; commercially available) and diisopropylethylamine (1.03 mL, 1.14 g, 8.84 mmol, 2.1 equiv) and the reaction mixture stirred at rt. After 1 h, water was added (50 mL) and the water phase extracted with dichloromethane (3×50 mL). The combined organic phases were dried over MgSO4, the organic solvent removed under reduced pressure and the crude oil purified with column chromatography on silica eluting with ethyl acetate/heptane (2:1) to afford 1.1 g (64%) of the title compound. 1H NMR (300 MHz, CDCl3): δ 1.46-1.50 (m, 2H), 1.47 (s, 9H), 1.94-2.02 (m, 2H), 2.10-2.13 (m, 2H), 2.20-2.26 (m, 2H), 2.34-2.47 (m, 2H), 2.95-2.97 (m, 2H), 3.10-3.22 (m, 1H), 3.90 (br s, 1H), 4.05 (br s, 2H), 5.24 (brs, 1H), 7.14 (d, J=8.6 Hz, 1H), 7.28 (brs, 1H), 7.33 (d, J=8.6 Hz, 1H), 7.41 (brs, 1H). 13C NMR (75 MHz, CDCl3): δ 18.05, 25.33, 28.41, 32.30, 40.85, 42.49, 50.45, 79.76, 108.41, 108.54, 113.47, 134.57, 143.38, 145.21, 154.70, 161.76, 173.04. MS (ISP): 413.1 [M−H]−.
