Synthesis
General procedure for the synthesis of 2-cyano-4-methyl-5-nitropyridine from zinc cyanide and 2-bromo-4-methyl-5-nitropyridine: In a round-bottomed flask 2-bromo-4-methyl-5-nitropyridine (104 g, 0.479 mol), zinc cyanide (79 g, 0.673 mol, 1.4 equiv.), and tetrakis(triphenylphosphine)palladium (0.023 mol, 5 mol%). Note: The use of a catalyst purchased from STREM significantly reduces the reaction time and increases the yield. DMF (900 mL) was degassed for 10 minutes and added to the solid mixture described above. The reaction mixture was heated in an oil bath until the internal temperature reached 80°C. When the internal temperature reached 80 °C, the color of the reaction solution changed from light yellow to light brown. Maintaining this temperature, the reaction mixture was stirred continuously for 3 hours and the reaction progress was monitored by TLC. After completion of the reaction, the solvent was removed under vacuum. The residue was dissolved in a mixture of dichloromethane and water and insoluble impurities were removed by filtration through diatomaceous earth. The organic layer was separated and the aqueous layer was extracted with dichloromethane. All organic extracts were combined, dried with anhydrous magnesium sulfate and concentrated. The concentrated residue was purified by column chromatography with the eluent gradually adjusted from 100% hexane to hexane/ethyl acetate (4:1). Finally, 65.8 g of the target product 2-cyano-4-methyl-5-nitropyridine was obtained by hexane recrystallization in 83% yield. The product was identified by 1H NMR (300 MHz, CDCl3): δ 2.71 (s, 3H), 7.73 (s, 1H), 9.20 (s, 1H).LCMS analysis: APCI, [M-H]-=162 u/e, TIC purity: 95%; UV purity: 95%.
References
[1] Patent: WO2005/103003, 2005, A2. Location in patent: Page/Page column 61-62
[2] Patent: US2006/155128, 2006, A1. Location in patent: Page/Page column 66
[3] Bioorganic and Medicinal Chemistry Letters, 2003, vol. 13, # 5, p. 795 - 798
