CN1CCOCC1.C(OC(Cl)=O)C(C)C.[C:16]([NH:26][C:27]([CH3:32])([C:29]([OH:31])=O)[CH3:28])([O:18][CH2:19][C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1)=[O:17].Cl.[CH3:34][NH:35][O:36][CH3:37].Cl>C(Cl)Cl>[CH3:37][O:36][N:35]([CH3:34])[C:29](=[O:31])[C:27]([NH:26][C:16](=[O:17])[O:18][CH2:19][C:20]1[CH:21]=[CH:22][CH:23]=[CH:24][CH:25]=1)([CH3:28])[CH3:32]N-Methylmorpholine (682 mg, 741 μL, 6.74 mmol) and isobutylchloroformate (460 mg, 441 μL, 3.37 mmol) were added successively to a stirred solution of N-carbobenzyloxy-2-methylalanine (0.64 g, 2.69 mmol) in dry CH2Cl2 at 0° C. under N2. The resulting cloudy mixture was stirred at 0° C. for 90 min. N,O-Dimethylhydroxylamine hydrochloride (316 mg, 3.24 mmol) was added portionwise and the mixture was warmed to room temperature and stirred for 3 h. The mixture was poured into 1N HCl (30 mL) and extracted with CH2Cl2 (3×40 mL). The combined extracts were washed with 1N HCl (30 mL), dried (Na2SO4) and concentrated in vacuo to give the crude product. This was purified by flash chromatography (Si, 40×160 mm, 0-80% EtOAc in hexanes gradient) to afford benzyl {2-[methoxy(methyl)amino]-1,1-dimethyl-2-oxoethyl}carbamate. Rf=0.47 (50% EtOAc in hexanes). LCMS calc.=303.1; found=303.2 (M+Na)+. 1H NMR (500 MHz, CDCl3) δ 7.37-7.29 (m, 5H), 5.82 (s, 1H), 5.09 (s, 2H), 3.60 (s, 3H), 3.18 (s, 3H), 1.60 (s, 6H).
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