Synthesis and reactions of 7‐substituted 1‐cyclopropyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐1,8‐naphthyridine‐3‐carboxylic acids as an antibacterial agent

Abstract 1‐Cyclopropyl‐ and 1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐1,8‐naphthyridine‐3‐carboxylic acid derivatives having a sulfinyl or sulfonyl group at C‐7 were synthesized from 2,6‐dichloro‐5‐fluoronicotinic acid derivatives by the route involving the Dieckmann‐type cyclization. The displacement reactions of these compounds with pyrrolidine and piperidine gave mainly the 7‐(1‐pyrrolidinyl)‐ and 7‐(1‐piperidinyl)‐1,8‐naphthyridine derivatives 24‐27, respectively. Enoxacin, a potent antibacterial agent, was also synthesized with the analogous route.