[OH:1][CH2:2][C@@H:3]([N:6]([CH2:14][C:15]([N:17]([O:19][CH3:20])[CH3:18])=[O:16])[C:7](=[O:13])[O:8][C:9]([CH3:12])([CH3:11])[CH3:10])[CH:4]=[CH2:5].S(OC)(O[CH3:25])(=O)=O.[Li+].C[Si]([N-][Si](C)(C)C)(C)C>C1COCC1>[CH3:20][O:19][N:17]([CH3:18])[C:15](=[O:16])[CH2:14][N:6]([C@@H:3]([CH:4]=[CH2:5])[CH2:2][O:1][CH3:25])[C:7](=[O:13])[O:8][C:9]([CH3:10])([CH3:11])[CH3:12]To a solution of (S)-tert-butyl 1-hydroxybut-3-en-2-yl(2-(methoxy(methyl)amino)-2-oxoethyl)carbamate (Intermediate 250, 7 g, 24.28 mmol) in THF (75 mL) at 0° C. was added dimethyl sulfate (2.436 mL, 25.49 mmol) followed by LiHMDS (26.7 mL, 26.70 mmol). The reaction mixture was allowed to warm slowly to room temperature and stirred for two hours. The reaction mixture was then partitioned between ethyl acetate and water. The layers were separated and the organics were washed with saturated sodium bicarbonate, water and brine. The organics were dried over magnesium sulfate, filtered and concentrated. Silica gel chromatography (5%-30% ethyl acetate/hexanes) afforded the title compound as a clear oil (6.89 g, 91%).
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