Reactions of N-Aminoquinolones with Ketones: A New Approach to the Synthesis of Tricyclic 6-Fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic Acids

Reactions of 7-(X)-substituted ethyl 1-amino-4-oxo-1,4-dihydroquinoline-3-carboxylates (1a-c; X = F, Cl and 4-methylpiperazin-1-yl) with mono- and di-ketones have been studied. Treatment of 1a; X = F with cyclopentanone and cyclopentanone in acetic acid resulted in the corresponding azomethynes; α-dicarbonyl compounds such as glyoxal, glyoxylic acid or ethyl pyruvate caused desamination of 1a into ethyl, 6,7-difluoro-4-oxo-1,4-dihydroquinoline-3-carboxylate, while reactions of 1a-c with acetoacetone resulted in tricyclic 7-fluoro-4-oxopyrazolo[1,5-a]quinoline-4-carboxylic acids