The general procedure for the synthesis of 7-fluoro-2-indolone from 2-(3-fluoro-2-nitrophenyl)acetic acid was as follows: 2-(3-fluoro-2-nitrophenyl)acetic acid (9.6 g, 48 mmol) was dissolved in acetic acid (100 mL), 10% palladium-carbon catalyst (1.3 g) was added, and the hydrogenation reaction was carried out for 24 h at 50 psi hydrogen pressure. Upon completion of the reaction, the catalyst was filtered through Celite to remove the catalyst. Subsequently, the solvent in the reaction solution was removed by evaporation. The resulting residue was dissolved in ethanol (100 mL), p-toluenesulfonic acid (50 mg) was added, and the mixture was heated to reflux for 1 hour. The reaction solution was cooled, poured into water and extracted with ethyl acetate, the organic phase was dried with anhydrous magnesium sulfate and the solvent was evaporated. Finally, the solid obtained was ground with hexane/ethyl acetate (95/5, v/v) mixed solvent to give 7-fluoro-1,3-dihydro-indol-2-one (6 g, 83% yield).
