10406-06-1

5-Bromo-1H-indole-3-carboxylic Acid is a useful intermediate used in the synthesis of indole derivatives that functions as inhibitors for the vascular endothelial growth factor receptor 2 (VEGFR-2) tyrosine kinase.

Lithium tert-butoxide (LiOtBu, 160 mg, 2.00 mmol) and 5-bromoindole (23.4 mg, 0.4 mmol) were added to a dry two-neck flask. The reaction vessel was evacuated and filled with carbon dioxide gas. Subsequently, N,N-dimethylformamide (DMF, 2 mL) was added and the mixture was stirred and reacted at 100 °C for 24 hours. Upon completion of the reaction, the mixture was cooled to room temperature, the reaction was carefully quenched with 2N hydrochloric acid solution and extracted with ethyl acetate (5 x 5 mL). The organic phases were combined, washed sequentially with water (2 x 5 mL) and saturated saline (1 x 5 mL) and dried over anhydrous magnesium sulfate. The dried organic phases were concentrated under reduced pressure and the residue was purified by preparative thin layer chromatography (Spreader: hexane/acetone=1:1, v/v) to afford the target compound 5-bromo-1H-indole-3-carboxylic acid (153.0 mg, 95% yield) as a white solid.

[1] Organic Letters, 2012, vol. 14, # 20, p. 5326 - 5329,4
[2] Heterocycles, 2015, vol. 90, # 2, p. 1196 - 1204