Phosphoric Acid → (5-methyl-1H-indol-4-yl)boronic acid

Temperature

-78 °C

A solution of 4-bromo-5-methylindole (800 mg, 3.8 mmol) in anhydrous ether (8 mL) is added with stirring to a suspension of potassium hydride (560 mg, 4.2 mmol, 30% dispersion in mineral oil) in anhydrous ether at 0° C. under argon. The resulting mixture is cooled to −78° C. and tert-butyllithium (4.9 mL of 1.7 M in pentane, 8.4 mmol) is slowly added. The resulting cream-colored mixture is stirred at −78° C. for 1 hour. Tributylborate (3.1 mL, 11.4 mmol) is slowly added and the reaction mixture is stirred for 1 hour at −78° C. before being allowed to slowly warm to room temperature. More anhydrous ether is added to facilitate stirring. After stirring for 24 h, the resulting sticky mixture is diluted with ether and transferred in portions with stirring to a precooled solution of 1 M phosphoric acid (50 mL). After stirring for 30 min, the acidic mixture is extracted with diethyl ether (75 mL×3) and the combined extracts are extracted with 1 N sodium hydroxide (20 mL×4). The combined base extracts are cooled with an ice bath, acidified with 1 M phosphoric acid and extracted with EtOAc (20 mL×3). The combined extracts are washed with brine (20 mL), dried over anhydrous sodium sulfate, filtered and concentrated to obtain a beige residue. The residue is triturated with hexane to obtain the desired 5-methylindole-4-boronic acid as a beige gum.

1. stirringthe reaction mixture is stirred for 1 hour at −78° C.
2. temperatureto slowly warm to room temperature
3. stirringto facilitate stirring
4. stirringAfter stirring for 24 h
5. stirringAfter stirring for 30 min
6. extractionthe acidic mixture is extracted with diethyl ether (75 mL×3)
7. extractionthe combined extracts are extracted with 1 N sodium hydroxide (20 mL×4)
8. temperatureThe combined base extracts are cooled with an ice bath
9. extractionextracted with EtOAc (20 mL×3)
10. washThe combined extracts are washed with brine (20 mL)
11. dry with materialdried over anhydrous sodium sulfate
12. filtrationfiltered
13. concentrationconcentrated
14. customto obtain a beige residue
15. customThe residue is triturated with hexane

ORD record

ord-735b6bceafe540bb9aa95a55d046181c

Source dataset

uspto-grants-2012_03

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US08129395B2