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General procedure for the synthesis of methyl 4-bromo-6-methoxypyridine-2-carboxylate from methyl 4-amino-6-methoxypyridine-2-carboxylate: To a 120 mL solution of acetonitrile containing 3.47 mL (29.3 mmol) of tert-butyl nitrite and 6.60 g (29.3 mmol) of copper(II) bromide, add slowly and dropwise at 40 °C 3.33 g (18.3 mmol) of methyl 4-amino-6-methoxypyridine-2-carboxylate dissolved in 30 mL of acetonitrile. The reaction mixture was stirred at 80 °C for 1 h and then poured into ice water. The precipitate was collected by filtration, washed with water and dried. The crude product was purified by fast chromatography (petroleum ether/ethyl acetate = 4/1 → 3/1) to give 2.50 g (56% yield) of the target product. eSI-MS: m/z = 246 (M + H)+.

[1] Patent: WO2013/87805, 2013, A1. Location in patent: Page/Page column 76
[2] Patent: US2013/158042, 2013, A1. Location in patent: Paragraph 0497; 0498; 0499; 0500