ethyl 1-(3-amino-4,6-difluorophenyl)-7-chloro-6-fluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylate

ethyl 7-chloro-1-(3-ethoxycarbonylamino-4,6-difluorophenyl)-6-fluoro-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylate

tert-butyl (2,4-difluoro-5-nitrophenyl)carbamate

ethyl 1-(5-tert-butoxycarbonylamino-2,4-difluorophenyl)-7-chloro-6-fluoro-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylate

2,6-dichloro-α-(ethoxymethylene)-5-fluoro-β-oxo-3-pyridinepropanoic acid ethyl ester