The condensation of 2,4-dichloro-5-fluorobenzoyl chloride (I) with diethyl malonate (II) by means of magnesium ethoxide in ether gives diethyl 2,4-dichloro-5-fluorobenzoylmalonate (III), which is partially hydrolyzed and decarboxylated with p-toluenesulfonic acid water yielding ethyl 2,4-dichloro-5-fluorobenzoylacetate (IV). The condensation of (IV) with triethyl orthoformate (V) in refluxing acetic anhydride affords ethyl 2-(2,4-dichloro-5-fluorobenzoyl)-3-ethoxyacrylate (VI), which is treated with cyclopropylamine (VII) in ethanol to give ethyl 2-(2,4-dichloro-5-fluorobenzoyl)-3-cyclopropylaminoacrylate (VIII). The cyclization of (VIII) with NaH in refluxing dioxane yields 7-chloro-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid (IX), which is finally condensed with piperazine (X) in hot DMSO.