7593-91-1

399-68-8

General procedure for the synthesis of 4-fluoroindole-2-carboxylic acid from the compound (CAS: 7593-91-1): 4.8 g (31 mmol) of compound 32 was dissolved in 60 mL of 4% NH4OH solution, which was subsequently added to a solution prepared from 52.45 g (188.7 mmol) of ferrous sulfate heptahydrate and 23 mL of concentrated NH4OH in 200 mL of water in a suspension of ferrous hydroxide. The reaction mixture was kept at boiling point for 5 minutes. Upon completion of the reaction, the resulting iron hydroxide precipitate was separated by filtration and washed repeatedly with dilute NH4OH and water. The filtrate was acidified with dilute HCl to a suitable pH and the precipitated solid was subsequently collected by filtration to afford 1.2 g (22% yield) of 4-fluoro-1H-indole-2-carboxylic acid (34) as a white solid. The resulting product could be used directly in the next step of the reaction without further purification.