Synthesis
The general procedure for the synthesis of 2-fluoropyridine-5-boronic acid from 2-fluoro-5-bromopyridine is as follows:
1. in a 72 L reactor equipped with a reflux condenser and temperature probe, 5-bromo-2-fluoropyridine (1.17 L, 0.568 mol), toluene (18.2 L) and triisopropyl borate (3.13 L, 0.68 mol, 1.2 eq.) were added and stirring was initiated.
2. tetrahydrofuran (4.4L) was added to the reactor and the reaction mixture was cooled to -35 to -50°C.
3. n-Butyllithium (2.5M hexane solution, 5.44L, 0.68mol, 1.2 eq.) was added slowly and dropwise while maintaining the temperature of the reaction mixture between -35 and -45 °C.
4. after 5 hours of reaction, confirming that the reaction is complete, the reaction mixture is slowly warmed to -15 to -20 °C.
5. 2M HCl (11.80L) was slowly added to the reaction mixture while maintaining the temperature between -15°C and 0°C.
6. The reaction mixture was stirred at 18 to 23 °C for 16 h followed by phase separation.
7. The organic phase was extracted with 6 M sodium hydroxide (6.0 L).
8. The acidic and basic aqueous phases were combined in a reactor and the pH was adjusted to 7.5 by slowly adding 6M HCl (2.5L).
9. Sodium chloride (6.0 kg) was added to the aqueous phase, followed by extraction with THF (3 x 20 L).
10. The organic phases were combined, dried with magnesium sulfate, and concentrated to give 1300 g of brown solid in 81% crude yield.
References
[1] Patent: WO2009/51848, 2009, A1. Location in patent: Page/Page column 65
[2] Tetrahedron, 2002, vol. 58, # 14, p. 2885 - 2890
[3] Journal of Medicinal Chemistry, 2005, vol. 48, # 1, p. 224 - 239
[4] Synthesis, 2003, # 7, p. 1035 - 1038
[5] Bioorganic and Medicinal Chemistry Letters, 2007, vol. 17, # 10, p. 2858 - 2862
