Bromine (115 g, 720 mmol) was added drop-wise to a suspension of 6-oxo-1, 6-dihydropyridine-2-carboxylic acid (25 g, 180 mmol) in acetic acid (400 mL). The reaction mixture was heated to 80° C. for 16 hours, whereupon it was concentrated to dryness under reduced pressure. The residue was triturated with tert-butyl methyl ether (200 mL) and filtered; the filter cake was washed with tert-butyl methyl ether (3×100 mL) to provide the product as a gray solid. Yield: 39.0 g, 179 mmol, 99percent.
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