The reduction of 4-fluoro-3-nitroaniline (I) with SnCl2.2H20 in concentrated aqueous HCl gives 4 fluoro-m-phenylenediamine (II), which is condensed with diethyl ethoxymethylenemalonate (III) in refluxing ethanol to afford diethyl 4-fluoro-3-aminoanilinomethylenemalonate (IV). The cyclization of (IV) by means of acetic anhydride in diphenyl oxide at 250 C yields ethyl 7-acetamido-4-hydroxy-6-fluoroquinoline-3-carboxylate (V), which is alkyiated with ethyl bromide and NaOH in refluxing ethanol to give 7-amino-6-fluoro-1-ethyl-1,4 dihydro-4-oxoquinoline-3-carboxylic acid (VI). Finally, this compound is condensed with 2,5-dimethoxytetrahydrofuran (VII) in hot acetic acid.