Synthesis of quinolonecarboxylic acids from 1,3,5-trinitrobenzene

Products of nucleophilic substitution for one NO₂ group in 1,3,5-trinitrobenzene were selectively reduced to 3-X-5-nitroanilines (X = CF₃CH₂O, PhO, PhS), which were converted by condensation with EtOCH=C(COOEt)₂ to the respective enamines; acid-catalysed cyclization of the latter gives esters of X-substituted 4-oxo-1,4-dihydroquinoline-3-carboxylic acids. The cyclization direction depends on the substituent type: ortho (X = CF₃CH₂O or PhO) or para (X = PhS) with respect to NO₂. N-Ethylation of these esters followed by hydrolysis gives the corresponding N-ethyl-5(7)-X-7(5)-nitroquinolinecarboxylic acids.