Synthesis
The general procedure for the synthesis of 2-hydroxy-4-chloro-5-nitropyridine from 4-chloro-3-nitropyridine was as follows: liquid ammonia (74.0 mL, 3418.64 mmol) was concentrated in tetrahydrofuran (THF, 170 mL) and cooled to -78 °C under nitrogen protection. Potassium tert-butoxide (23.98 g, 213.67 mmol) solid was added to this solution and the reaction mixture was subsequently slowly warmed to -35 °C. In another vessel, tert-butyl hydroperoxide (5.5 M dissolved in decane, 16.32 mL, 89.74 mmol) was added dropwise to a solution of 4-chloro-3-nitropyridine (13.55 g, 85.47 mmol) in THF (200 mL), and this process was carried out under nitrogen protection at 0 °C for 5 min. This resulting solution was slowly added to the aforementioned reaction mixture and stirred at -35 °C for 1.5 hours. Upon completion of the reaction, the reaction was quenched with saturated ammonium chloride solution (50 mL) and the mixture was allowed to slowly warm up to room temperature overnight. Subsequently, the reaction mixture was concentrated under reduced pressure and the precipitated brown precipitate was filtered and washed with cold water to give the crude product. Finally, the solid was dried under vacuum overnight to afford 4-chloro-5-nitropyridin-2-ol (14.66 g, 83.99 mmol, 98% yield) as a yellow solid. The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 6.36 (1H, s), 8.73 (1H, s). Mass spectrum (m/z): 173 ([M-H]-).
References
[1] Patent: WO2009/24821, 2009, A2. Location in patent: Page/Page column 156-157
[2] Patent: EP2818472, 2014, A1. Location in patent: Paragraph 0126; 0127
[3] Tetrahedron Letters, 2010, vol. 51, # 21, p. 2800 - 2802
[4] Patent: WO2015/115673, 2015, A1. Location in patent: Page/Page column 79-80
[5] Journal of Medicinal Chemistry, 2007, vol. 50, # 1, p. 2 - 5
