Reaction Steps
A mixture of N2-(cis-3-benzyloxycyclobutyl)-4-fluorobenzene-1,2-diamine (1.13 g, 3.95 mmol), (S)-2-tertbutoxycarbonylaminopropionic acid (0.83 g, 4.35 mmol) and HOAt (0.59 g, 4.35 mmol) in DCM (20 mL) was cooled to 0° C. under nitrogen atmosphere. To this mixture N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (0.83 g, 4.35 mmol) was added portion wise and the reaction mixture stirred at RT for 1 h. The reaction mixture allowed to warm to RT then partitioned between DCM and a 10% aq. citric acid. The organic fraction was washed with brine (20 mL), dried (MgSO4), concentrated in vacuo and the resulting dark brown residue purified by column chromatography (Si—PCC, gradient 0-40% EtOAc in cyclohexane) to afford the title compound as a yellow gum, which solidified on standing (1.93 g, 93%). 1H NMR (CDCl3, 400 MHz): δ 7.46 (1H, s, br), 7.36-7.30 (5H, m), 7.11 (1H, q, J=14.8 Hz, 2.5 Hz), 6.37 (1H, dt, J=19.5 Hz, 2.8 Hz), 6.25 (1H, dd, J=14 Hz, 2.82 Hz), 4.94 (1H, d, J=5.83 Hz), 4.43 (2H, s), 4.23-4.07 (1H, m), 3.93-3.81 (1H, m), 3.47-3.35 (1H, m), 2.88-2.75 (1H, m), 2.03-1.85 (1H, m), 1.45 (3H, d, J=2.46 Hz), 1.43 (9H, s). LCMS (Method B): RT 3.88 min [M+H]+ 458. 110183151. The compound thus obtained (1 g, 2.19 mmol) was dissolved in AcOH (15 mL) and heated at 70° C. for 18 h. After cooling to RT, the volatiles were evaporated under reduced pressure and the residue partitioned between DCM (40 mL) and a saturated solution of NaHCO3 (20 mL). The organic fraction was washed with brine (20 mL), dried (MgSO4) and concentrated in vacuo. The resulting dark yellow residue was purified by column chromatography (Si—PCC, gradient 0-50% EtOAc in cyclohexane) to afford the title compound as pale red gum (570 mg, 60%). LCMS (Method B): RT 3.61 min [M+H]+ 440.0. 1H NMR (CDCl3, 400 MHz): δ 7.70-7.60 (2H, m), 7.44-7.37 (5H, m), 7.05-6.96 (1H, m), 5.38-5.26 (1H, m), 5.20-5.05 (1H, m), 4.82-4.68 (1H, m), 4.55 (2H, s), 4.10-3.97 (1H, m), 3.02-2.77 (4H, m), 1.47 (3H, d, J=2.44 Hz), 1.44 (9H, s).
