Synthesis
Sodium metal (4.60 g, 200 mmol) was added in batches to anhydrous ethanol (100 mL) under nitrogen protection, keeping the reaction temperature at 0-5 °C. The mixture was stirred to slowly warm up to room temperature over 18 hours. Subsequently, 3,5-dibromopyridine (31.5 g, 133 mmol) and N,N-dimethylformamide (DMF, 100 mL) were added to the reaction system. The reaction mixture was heated to 70 °C with continuous stirring for 48 hours. After completion of the reaction, the brown mixture was cooled to room temperature, slowly poured into water (600 mL) and extracted with ether (3 x 500 mL). The ether extracts were combined, dried with anhydrous sodium sulfate, filtered and concentrated by rotary evaporator. The final product was purified by vacuum distillation to give 22.85 g (85.0% yield) of 5-bromo-3-ethoxypyridine as an oil with a boiling point of 89-90 °C (2.8 mmHg). A boiling point of 111 °C (5 mmHg) has been reported in the literature (see K. Clarke et al., J. Chem. Soc. 1885 (1960)).
References
[1] Patent: WO2006/23630, 2006, A2. Location in patent: Page/Page column 60
[2] Journal of Medicinal Chemistry, 2009, vol. 52, # 14, p. 4126 - 4141
[3] Patent: WO2010/96389, 2010, A1. Location in patent: Page/Page column 37; 39
[4] Patent: WO2010/135014, 2010, A1. Location in patent: Page/Page column 45-47
[5] Patent: WO2011/87776, 2011, A1. Location in patent: Page/Page column 48; 51
