Synthesis
The general procedure for the synthesis of 2-amino-5-bromo-3-benzyloxypyridine from 2-amino-3-benzyloxypyridine was as follows: 2-amino-3-benzyloxypyridine (85.0 g, 0.42 mol) was dissolved in 10% aqueous sulfuric acid solution (1000 mL). The resulting yellow solution was cooled to 0 to 4°C, followed by slow dropwise addition of a solution of bromine (80.5 g, 0.50 mol) in acetic acid (276 g, 4.6 mol) over a period of 2 hours. The reaction mixture was transformed into a red suspension and stirring was continued at 0°C for 2.5 hours. The reaction mixture was poured into a mixture of ice water (500 mL) and dichloromethane (1000 mL), and the pH was adjusted to 8 by adding a 25% ammonia solution (~600 mL) while stirring the two-phase mixture thoroughly. The organic and aqueous phases were separated and the aqueous phase was further extracted with dichloromethane (3 x 500 mL). All organic phases were combined, washed with water (400 mL) and dried with sodium sulfate. The solvent was removed by concentration under reduced pressure and the residue was purified by fast column chromatography [silica gel 1 kg, eluent: petroleum ether/ethyl acetate = 7:3 (v/v)]. The final product was 96.0 g of 2-amino-5-bromo-3-benzyloxypyridine as a brown solid in 81% yield. The melting point of the product was 109-110°C. 1H-NMR (CDCl3, 200 MHz) data were as follows: δ = 4.73 (broad single peak, 2H), 5.04 (single peak, 2H), 7.08 (double peak, 1H), 7.40 (multiple peaks, 5H), 7.73 (double peaks, 1H).
References
[1] Journal of Medicinal Chemistry, 2013, vol. 56, # 19, p. 7669 - 7678
[2] Journal of Medicinal Chemistry, 2007, vol. 50, # 24, p. 6240 - 6264
[3] Patent: WO2005/58325, 2005, A1. Location in patent: Page/Page column 39
[4] Patent: WO2005/90358, 2005, A2. Location in patent: Page/Page column 74
[5] Journal of the American Chemical Society, 2015, vol. 137, # 27, p. 8851 - 8857
