C(OC(=O)[NH:7][C:8]1[C:9]([C:16]#N)=[N:10][C:11]([Cl:15])=[CH:12][C:13]=1[CH3:14])(C)(C)C.[OH2:19].[OH-:20].[Na+]>S(=O)(=O)(O)O>[NH2:7][C:8]1[C:9]([C:16]([OH:20])=[O:19])=[N:10][C:11]([Cl:15])=[CH:12][C:13]=1[CH3:14](6-Chloro-2-cyano-4-methyl-pyridin-3-yl)-carbamic acid tert-butyl ester (3.72 g) was dissolved in concentrated sulfuric acid (19 mL) and stirred for 1 h at 100° C. The reaction mixture was cooled to room temperature and water (19 mL) was slowly added. The reaction mixture was warmed again to 100° C. and stirred at this temperature for 2 h. Water was added after cooling to room temperature, the mixture was cooled in an ice bath and the pH was adjusted to ˜14 by slow addition of solid sodium hydroxide. The aqueous solution was washed 2× with MTB-ether, the aqueous layer was then adjusted to pH ˜2 by addition of 5 M hydrochloric acid and extracted 3× with ethyl acetate. The combined organic layer was washed with brine, dried over magnesium sulfate and concentrated in vacuum to afford 2.25 g of the title compound of the formula
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