[C:1]([O:5][C:6]([NH:8][C:9]1[S:10][C:11]([C:15]([OH:17])=[O:16])=[C:12]([CH3:14])[N:13]=1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[H-].[Na+].IC.[C:22](=O)(O)[O-].[Na+]>CN(C)C=O>[C:1]([O:5][C:6]([N:8]([CH3:22])[C:9]1[S:10][C:11]([C:15]([OH:17])=[O:16])=[C:12]([CH3:14])[N:13]=1)=[O:7])([CH3:4])([CH3:2])[CH3:3]To a stirred solution of 2-(tert-butoxycarbonylamino)-4-methylthiazole-5-carboxylic acid (0.13 g, 0.50 mmol) in N,N-dimethylformamide (2.5 mL) at 0° C. was added sodium hydride (0.044 g, 1.10 mmol, 60% dispersed in mineral oil). The resultant mixture was stirred at 0° C. for 40 min, followed by the dropwise addition of iodomethane (31.2 mL, 0.50 mmol). The resultant solution was allowed to warm to ambient temperature over 18 h, followed by the addition of saturated sodium bicarbonate solution. The mixture was extracted with ethyl acetate. The combined organic layer was dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo. The crude product was purified by flash column chromatography eluting with ethyl acetate/hexanes (50/50 to 100/0) to afford 2-(tert-butoxycarbonyl(methyl)amino)-4-methylthiazole-5-carboxylic acid (0.070 g, 0.26 mmol).
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