Regioselective Displacement Reactions of 1-Cyclopropyl-5, 6, 7, 8-tetrafluoro-4(1H)-oxoquinoline-3-carboxylic Acid with Amine Nucleophiles

Abstract

The displacement reactions of ethyl 1-cyclopropyl-5, 6, 7, 8-tetrafluoro-4(1H)-oxoquinoline-3-carboxylate (7) and its carboxylic acid 8 with amine nucleophiles were examined. The nucleophilic displacement occurred regioselectively at the C-5 or C-7 position depending on the substrate (7 or 8) and solvent selected; this finding permitted the introduction of an optional nucleophile preferentially into the required position at either C-5 or C-7, or into both positions with a desired combination of nucleophiles. Taking advantage of this regioselectivity, we prepared various 5-substituted 6, 7, 8-trifluoro- and 7-substituted 5, 6, 8-trifluoro-1-cyclopropyl-4(1H)-oxoquinoline-3-carboxylic acids. Furthermore, the use of the boron-chelated derivative of the carboxylic acid 8 was favorable for the regioselective synthesis of 7-substituted 5, 6, 8-trifluoroquinolones.