O=[C:2]1[CH2:5][N:4]([C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7])[CH2:3]1.[CH3:13][NH:14][CH:15]1[CH2:18][CH2:17][CH2:16]1.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>C(Cl)Cl.C(OCC)(=O)C>[CH:15]1([N:14]([CH3:13])[CH:2]2[CH2:5][N:4]([C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7])[CH2:3]2)[CH2:18][CH2:17][CH2:16]1Combined a solution of tert-butyl 3-oxoazetidine-1-carboxylate (500 mg, 2.92 mmol) and N-methylcyclobutanamine (0.373 mL, 3.50 mmol) in methylene chloride (15 mL) and added sodium triacetoxyborohydride (929 mg, 4.38 mmol) and the solution stirred at 20° C. for 3 h. The solution was concentrated in vacuo to give a white solid. The solid was taken up in ethyl acetate (50 mL), washed with saturated sodium bicarbonate (50 mL) and brine, dried with magnesium sulfate, and concentrated in vacuo to give a residue which was purified on a 40 g silica gel column eluted with 0 to 70% ethyl acetate in hexanes to give the title compound (342 mg, 1.423 mmol, 48.7%) as a clear, colorless oil. 1H NMR (400 MHz, METHANOL-d4) δ ppm 1.43 (s, 9 H) 1.60-1.75 (m, 2 H) 1.85-2.04 (m, 4 H) 2.07 (s, 3 H) 2.81-2.94 (m, 1 H) 3.27-3.30 (m, 1 H) 3.81-3.88 (m, 2 H) 3.88-3.97 (m, 2 H); MS: 241 (M+H).
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