Synthesis
Step 3: NaH (60% oil dispersion, 2.32 g, 58 mmol) was slowly added to a solution of diethyl malonate (8.8 mL, 58 mmol) ether (110 mL) cooled to 15 °C over 5 min. Subsequently, 3-bromo-2-chloro-5-nitropyridine (12.5 g, 52.6 mmol) was added in four batches over a period of 15 min, and the temperature was observed to rise to 26 °C during the reaction. Upon completion of the reaction, the ether was removed by distillation under reduced pressure to give a red oily substance. This oily substance was stirred at 114 °C for 1 h 15 min and then 6 M H2SO4 (67 mL) was added. The mixture was heated to reflux for 8 h. After cooling to 0 °C, the pH was adjusted to 7 with 25% aqueous KOH (135 mL). The mixture was stirred in an ice bath for 25 min, the crude product was collected by filtration and washed with 50 mL of water. The crude product was dissolved in CH2Cl2 (350 mL), stirred for 30 min and filtered to remove insoluble material. The organic layer was dried with Na2SO4, filtered and concentrated to give 11.1 g of impure red oily product. This oily product was dissolved in CH2Cl2 (100 mL) and hexane (200 mL), filtered and the organic phase was concentrated to give 9.3 g of 3-bromo-2-methyl-5-nitropyridine as an orange crystalline solid in 81% yield.1H NMR (CDCl3) δ 9.25 (d, J = 2.3 Hz, 1H), 8.61 (d, J = 2.3 Hz, 1H), 2.80 (s, 3H).
References
[1] Patent: US2006/79522, 2006, A1. Location in patent: Page/Page column 8; 13
[2] Patent: US2006/79523, 2006, A1. Location in patent: Page/Page column 9; 13-14
[3] Patent: US2006/79524, 2006, A1. Location in patent: Page/Page column 13
[4] Patent: US2006/79683, 2006, A1. Location in patent: Page/Page column 8; 12
[5] Patent: CN103130792, 2016, B. Location in patent: Paragraph 0722-0724
