Treatment of 2,4-difluorophenylacetic acid (I) with NaOH in dimethylimidazolinone at 135 C afforded 4-fluorosalicylic acid (II). After activation of (II) with SOCl2, coupling with 3-nitrobenzylamine (III) gave amide (IV). Subsequent O-alkylation of (IV) by means of ethyl bromoacetate (A) and K2CO3 yielded ether (V). Conversion of the amide function of (V) to the corresponding thioamide (VI) was accomplished using phosphorus pentasulfide (P4S10) in pyridine. Finally, the ester group of (VI) was hydrolyzed with NaOH to the title carboxylic acid.