Synthesis of fluorinated pyridines by the balz‐schiemann reaction. An alternative route to enoxacin, a new antibacterial pyridonecarboxylic acid

Fluorination of the 2,6‐disubstituted 3‐aminopyridines 5 and 12 by the Balz‐Schiemann reaction is described. 2,6‐Dichloro‐3‐pyridinediazonium tetrafluoroborate (6) and 2‐substituted 6‐acetylamino‐3‐pyridinediazonium tetrafluoroborates 13 were heated with or without a solvent to give the corresponding fluorinated pyridines 7 and 14, respectively, in good yields. 2‐Substituted 6‐acetylamino‐3‐fluoropyridines (14) were converted by a known method into a series of 7‐substituted 1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐1,8‐naphthyridine‐3‐carboxylic acids 21 including enoxacin [1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐(1‐piperazinyl)‐1,8‐naphthyridine‐3‐carboxylic acid [(2)], a new potential antibacterial agent.