New approach to [a]-fused fluoroquinolones: the synthesis of 5-oxo-1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinolines

The reaction of N-(ethoxycarbonyl)methyl substituted ethyl 6,7-difluoro-, 6 ,7,8-trifluoro- and 5,6,7,8-tetrafluoro-4-oxo-1,4-dihydroquinoline-3-carbox ylates with methyl methacrylate results in the [3 + 2] adducts, hexahydropy rrolo[1,2-a]quinolones, which can be precursors of [a]-fused fluoroquinolon es.