[C:1]([O:5][C:6]([NH:8][CH:9]([C:13]([CH3:17])([CH3:16])[CH:14]=[CH2:15])[C:10]([OH:12])=[O:11])=[O:7])([CH3:4])([CH3:3])[CH3:2].[C:18](=O)(O)[O-].[Na+].CI.O>CN(C=O)C>[C:1]([O:5][C:6]([NH:8][CH:9]([C:13]([CH3:17])([CH3:16])[CH:14]=[CH2:15])[C:10]([O:12][CH3:18])=[O:11])=[O:7])([CH3:4])([CH3:3])[CH3:2]
To a stirred mixture of 2(R/S)-(tert-butoxycarbonyl)amino-3,3-dimethyl-4-pentenoic acid (3.6 g, 15 mmol) and anhydrous sodium bicarbonate (3.78 g, 45 mmol) in 25 mL of DMF was added methyl iodide (1.03 mL, 17 mmol) dropwise. The mixture was stirred for 27 hours at room temperature, and then poured into water (100 mL). The mixture was extracted with 2:1 ethyl acetate:hexane (3×50 mL), and the combined organic layers were washed with 5% aq. sodium thiosulfate solution, water, sat. aq. sodium bicarbonate, and finally with brine. The organic layer was dried over magnesium sulfate, and concentrated to provide methyl 2(R/S)-(tert-butoxycarbonyl)amino-3,3-dimethyl4-pentenoate (3.37 g, 87%) as a syrup which was used without further purification.
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