Synthesis and antibacterial activity of 2,3-dehydroofloxacin

The 2,3-dehydro analog 2 of the potent quinolone antibacterial agent ofloxacin (1) was synthesized by an efficient six step route beginning with ethyl 2,3,4,5-tetrafluorobenzoylacetate. Formation of the oxazine ring of 2 was accomplished by ozonolysis of 1-(1-buten-3-yl)quinolone 5 to the corresponding aldehyde, which cyclized upon treatment with base via intramolecular displacement of the C-8 fluorine to afford tricyclic ester 6. The antibacterial activities of 2,3-dehydroofloxacin (2) and ofloxacin (1) are compared.