[C:1]([O:5][C:6]([NH:8][C:9]1[C:14]([C:15]([OH:17])=[O:16])=[CH:13][C:12]([Cl:18])=[N:11][CH:10]=1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH3:19][Si](C=[N+]=[N-])(C)C>CO.C(Cl)(Cl)Cl>[C:1]([O:5][C:6]([NH:8][C:9]1[C:14]([C:15]([O:17][CH3:19])=[O:16])=[CH:13][C:12]([Cl:18])=[N:11][CH:10]=1)=[O:7])([CH3:4])([CH3:2])[CH3:3]To 5.4 g of 5-tert-butoxycarbonylamino-2-chloro-isonicotinic acid in 50 mL of methanol and 100 mL of chloroform was at 0° C. was added 15 mL of 2 M (trimethylsilyl)diazomethane in hexanes. After allowing the reaction to warm to ambient temperature and stirring for 2 hours, the solvents were removed and the crude product purified by passing through a plug of silica gel with chloroform. The product was then recrystallized from hexanes to give 5.8 g (100%) of 5-tert-butoxycarbonylamino-2-chloro-isonicotinic acid, methyl ester: mp=90-96° C. (decomposed); mass spectrum (m/e): M+H 287.1.
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