O.[NH2:2][C:3]1[N:8]=[C:7]([CH:9]2[CH2:11][CH2:10]2)[N:6]=[C:5]([C:12]([OH:14])=[O:13])[C:4]=1[Cl:15].[C:16](=O)(OC)OC.S(=O)(=O)(O)O.[OH-].[Na+]>O.CO>[NH2:2][C:3]1[N:8]=[C:7]([CH:9]2[CH2:11][CH2:10]2)[N:6]=[C:5]([C:12]([O:14][CH3:16])=[O:13])[C:4]=1[Cl:15]A 500 mL multi-neck flask equipped with nitrogen bubbler, addition funnel, reflux condenser, and thermocouple was charged with 6-amino-5-chloro-2-cyclopropyl-4-pyrimidinecarboxylic acid monohydrate (47.8 g, 0.206 mol), methanol (32 g) and dimethyl carbonate (94.5 g, 1.05 mol). Concentrated sulfuric acid (50.0 g, 0.500 mol) was added over about 30 minutes with cooling to maintain the temperature below 60° C., and then the reaction mixture was heated at 70° C. for 10 h. The resulting mixture was cooled to 15° C. and diluted with 250 mL of water. The pH of the reaction mass was raised to 5-8 by adding about 42.7 g (0.534 mol) of 50 wt % aqueous NaOH over 30 minutes with cooling to maintain the temperature in the range of 10-15° C. The resulting slurry was cooled to 5° C. and filtered. The filtered wet cake was washed with water and dried to constant weight at 50° C. to give 43.3 g (93.5% yield) of the title compound with 98% purity as a solid melting at 147-148° C.
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