Synthesis
General procedure for the synthesis of methyl 2,6-dibromoisonicotinate from methanol and citrazinic acid: citrazinic acid (5.0 g, 32.2 mmol) was mixed with phosphorus tribromide (POBr3, 27.5 g, 96.8 mmol) and the reaction was heated at 130 °C. Upon completion of the reaction, the reaction mixture was cooled to 0 °C and methanol (250 mL) was slowly added to quench the reaction. Subsequently, the mixture was concentrated under reduced pressure and later separated by extraction with dichloromethane and saturated sodium bicarbonate solution. The aqueous layer was washed with saturated sodium bicarbonate solution. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to give a brown solid product. The product was analyzed by nuclear magnetic resonance (NMR) and liquid chromatography-mass spectrometry (LCMS) to confirm that the purity was sufficient for the subsequent reaction (79% yield, 7.5 g). Mass spectrometry (ESI) m/z: 295.8 (M+1). 1H NMR (400 MHz, CD2Cl2) δppm: 8.10 (s, 2H), 4.05 (s, 3H).
References
[1] Journal of Medicinal Chemistry, 2010, vol. 53, # 15, p. 5422 - 5438
[2] Patent: WO2009/150230, 2009, A1. Location in patent: Page/Page column 65
[3] European Journal of Inorganic Chemistry, 2010, # 13, p. 1913 - 1928
[4] Journal of Organic Chemistry, 2006, vol. 71, # 12, p. 4696 - 4699
[5] Synthesis, 2008, # 17, p. 2764 - 2770
