Trimethyl borate → 3-Pyridinylboronic acid

A solution of 4.0 ml (6.56 g, 42 mmol) of 3-bromopyridine and 9 ml (8 mmol) of trimethylborate in 100 ml of diethyl ether was cooled to -70° C. then treated slowly with 33 ml (83.8 mmol) of a 2.54M tert-butyllithium in pentane solution. After allowing the resulting slurry to warm to room temperature the solvents were evaporated under vacuum. The residual oil was treated carefully with 50 ml of a 1M hydrochloric acid solution. Several milliters of methylene chloride were added and the mixture was stirred until the oil had dissolved. The aqueous layer was washed with fresh methylene chloride. The pH of the aqueous solution was raised to 12 with 5M sodium hydroxide solution and the washing was repeated. The pH of the aqueous solution was then lowered to 6.5 with concentrated hydrochloric acid solution. After chilling, this solution was filtered, saturated with sodium chloride, then extracted several times with a 2:1 mixture of diethyl ether and isopropanol. Evaporation of these extracts produced a colorless solid. This material was further purified by dissolving in methanol, evaporating to a thick paste, adding a few milliters of water, concentrating further under vacuum, then chilling and collecting the crystalline product. Additional product in the aqueous mother liquor was isolated by repeating this process. Thorough drying of this hydrated product at 0.1 mm pressure afforded a fine powder weighing 2.2 g. Elemental analysis and a mass spectrum indicated the product so isolated was primarily the anhydride (tripyridylboroxane).

1. customwere evaporated under vacuum
2. additionThe residual oil was treated carefully with 50 ml of a 1M hydrochloric acid solution
3. additionSeveral milliters of methylene chloride were added
4. dissolutionhad dissolved
5. washThe aqueous layer was washed with fresh methylene chloride
6. temperatureThe pH of the aqueous solution was raised to 12 with 5M sodium hydroxide solution
7. temperatureAfter chilling
8. filtrationthis solution was filtered, saturated with sodium chloride
9. extractionextracted several times
10. additionwith a 2:1 mixture of diethyl ether and isopropanol
11. customEvaporation of these extracts
12. customproduced a colorless solid
13. customThis material was further purified
14. dissolutionby dissolving in methanol
15. customevaporating to a thick paste
16. additionadding a few milliters of water
17. concentrationconcentrating further under vacuum
18. temperaturechilling
19. customcollecting the crystalline product
20. customAdditional product in the aqueous mother liquor was isolated
21. customThorough drying of this hydrated product at 0.1 mm pressure
22. customafforded a fine powder
23. customso isolated

ORD record

ord-ed13c97cbeb948bda6aee994a95925f6

Source dataset

uspto-grants-1997_05

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US05633273