C([N-]C(C)C)(C)C.[Li+].[CH2:9]([N:16]1[C:22](=[O:23])[CH2:21][CH2:20][O:19][CH2:18][CH:17]1[CH3:24])[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1.CN(P(N(C)C)(N(C)C)=O)C.C([C:38]([O:40][CH3:41])=[O:39])#N>C1COCC1>[CH2:9]([N:16]1[C:22](=[O:23])[CH:21]([C:38]([O:40][CH3:41])=[O:39])[CH2:20][O:19][CH2:18][CH:17]1[CH3:24])[C:10]1[CH:11]=[CH:12][CH:13]=[CH:14][CH:15]=1
A solution of lithium diisopropylamide in THF (0.101 M, 100 mL, 10.1 mmol, 1.30 equiv) freshly prepared at −78° C. was added via cannula to a solution of 4-benzyl-3-methyl-1,4-oxazepan-5-one (4-3, 1.71 g, 7.80 mmol, 1 equiv) in THF (100 mL) at −78° C. and the resulting mixture was stirred for 20 min. HMPA (1.36 mL, 7.80 mmol, 1.00 equiv) was added followed by methyl cyanoformate (1.24 mL, 15.6 mmol, 2.00 equiv). The resulting mixture was warmed to 0° C., stirred for 20 min, and then partitioned between saturated aqueous ammonium chloride solution and ethyl acetate (2×150 mL). The combined organic layers were dried over sodium sulfate and concentrated. The residue was purified by flash column chromatography (20% EtOAc in hexanes initially, grading to 100% EtOAc) to give methyl 4-benzyl-3-methyl-5-oxo-1,4-oxazepane-6-carboxylate (4-4) as a mixture of diastereomers (colorless oil). LRMS m/z (M+H) 278.2 found, 278.1 required.
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