General procedure for the synthesis of 5-bromo-6-hydroxypyridinecarboxylic acid from 6-hydroxypyridine-2-carboxylic acid: bromine (115 g, 720 mmol) was added dropwise 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 and kept for 16 hours. Upon completion of the reaction, the mixture was concentrated to dryness under reduced pressure. The residue was ground with tert-butyl methyl ether (200 mL) and subsequently filtered. The filter cake was washed with tert-butyl methyl ether (3 x 100 mL) to give a gray solid product. Yield: 39.0 g, 179 mmol, 99% yield. The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 8.03 (d, J = 7.3 Hz, 1H), 6.83 (d, J = 7.3 Hz, 1H).
