Method of producing a quinolonecarboxylic acid derivative

The present invention is a method of producing a 6-fluoro-7-substituted quinolonecarboxylic acid derivative represented by the general formula (4): n the specification, which is characterized by adding an alkylboric acid ester represented by the general formula (3): B (OR5)3(3) wherein R5 represents a lower alkyl group, an aryl group, a substituted aryl group or a substituted aralkyl group to a 6-fluoroquinolonecarboxylic acid derivative represented by the general formula (1): (1) wherein R1 and R2 are as defined in the specification; and R3 represents an optional, functional residue capable of participating in a nucleophilic substitution reaction, and a substituted saturated heterocyclic amine represented by the general formula (2): (2) wherein X, Y and n are as defined in the specification, and condensing the reaction mixture with heating.