3-Chloro-4-fluoroaniline (I), condensed by heating at 125 C with diethyl ethoxymethylenemalonate (A), gives diethyl 3-chloro-4-fluoroanilinomethylenemalonate (II). The thermal cyclization of (II) by reflux in A Dowtherm gives ethyl 6-fluoro-7-chloro-4-hydroxyquinoline-3-carboxylate (III), which, alkylated by ethyliodide in DMF with potassium carbonate, leads to ethyl 1-ethyl-6 fluoro-7-chloro-4-oxo-1,4-dihydroquinoline-3-carboxylate (IV), purified by recrystallization. The ester (IV), after saponification and acidification, provides the corresponding acid (V). 1-Ethyl-6-fluoro-7-chloro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (V), heated to 100 C in pyridine with 1-methylpiperazine (B), leads to 1-ethyl-6-fluoro-7-(4-methyl-1-piperazinyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (VI). The salification of (VI) with methanesulfonic acid provides the salt.

3-Chloro-4-fluoroaniline (I), condensed by heating at 125 C with diethyl ethoxymethylenemalonate (A), gives diethyl 3-chloro-4-fluoroanilinomethylenemalonate (II). The thermal cyclization of (II) by reflux in A Dowtherm gives ethyl 6-fluoro-7-chloro-4-hydroxyquinoline-3-carboxylate (III), which, alkylated by ethyliodide in DMF with potassium carbonate, leads to ethyl 1-ethyl-6 fluoro-7-chloro-4-oxo-1,4-dihydroquinoline-3-carboxylate (IV), purified by recrystallization. The ester (IV), after saponification and acidification, provides the corresponding acid (V). 1-Ethyl-6-fluoro-7-chloro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (V), heated to 100 C in pyridine with 1-methylpiperazine (B), leads to 1-ethyl-6-fluoro-7-(4-methyl-1-piperazinyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (VI). The salification of (VI) with methanesulfonic acid provides the salt.