Synthesis
The general procedure for the synthesis of 4-chloro-5-bromopyrimidine using 5-bromopyrimidin-4-one as starting material was as follows: to a mixture of 5-bromopyrimidin-4-ol (40 g, 0.22 mol) dissolved in POCl3 (300 mL) was added drop-wise DIPEA (29 g, 0.22 mol) at room temperature. Subsequently, the reaction mixture was heated to reflux and maintained for 3 hours. The progress of the reaction was monitored by TLC (unfolding agent ratio of petroleum ether/EtOAc 1:1) to confirm the completion of the reaction. Upon completion of the reaction, excess POCl3 was removed by distillation under reduced pressure. the residue was slowly poured into ice water (300 mL) under stirring. The aqueous phase was extracted with EtOAc (2 × 300 mL), the organic layers were combined and washed sequentially with water (300 mL) and brine (300 mL), dried over Na2SO4 and finally concentrated under vacuum. The residue was purified by silica gel column chromatography (eluent ratio of petroleum ether/EtOAc, gradient from 20:1 to 10:1) to afford the target product 5-bromo-4-chloropyrimidine (25 g, 60% yield) as a yellow oil.
References
[1] Patent: WO2016/97918, 2016, A1. Location in patent: Page/Page column 88
[2] Patent: WO2012/135631, 2012, A1. Location in patent: Page/Page column 21-22
[3] Patent: WO2010/88518, 2010, A2. Location in patent: Page/Page column 86-87
[4] Organic Process Research and Development, 2000, vol. 4, # 4, p. 275 - 285
