Process for 6,7-dihydro-9-fluoro-5-methyl-1-oxo-1H,5H-benzo(ij)quinolizine-2-carboxy lic acid

A process for the preparation of flumequine comprising:

• a. reacting 4-fluoroaniline with a reactant selected from the group consisting of crotonaldehyde, a precursor for crotonaldehyde which generates crotonaldehyde under acidic conditions, and an alcoholic solution of crotonaldehyde or said precursor for crotonaldehyde in the presence of dilute aqueous acid between about 50.degree. and 60.degree. C. to provide a compound of the formula ##STR4## wherein R is hydrogen or alkyl having one, two or three carbon atoms;
• b. heating and removing water from the product of step (a) by slowly adding the product to a refluxing solvent which forms a binary azeotrope with water and has a boiling point between 90.degree. and 120.degree. C. to provide a mixture of 6-fluoroquinaldine and 6-fluorotetrahydroquinaldine as acid salts;
• c. treating said acid salts with base in the presence of weak acid followed by reducing the mixture to provide 6-fluorotetrahydroquinaldine;
• d. condensing said 6-fluorotetrahydroquinaldine with a dialkyl alkoxymethylenemalonate to provide a compound of the formula ##STR5## e. cyclizing the product of step (d) by heating in the presence of polyphosphoric acid followed by saponifying to provide flumequine.