4-(trifluoromethyl)quinoline derivatives

Under carefully controlled conditions, ethyl 4,4,4-trifluoroacetoacetate (ethyl 4,4,4-trifluoro-3-oxobutanoate) can be condensed with anilines and subsequently cyclized to give 4-trifluoromethyl-2-quinolinones 1 although only in poor yield. Heating these products with phosphoryl tribromide affords 2-bromo-4-(trifluoromethyl)quinolines 2 which can be converted into 4-(trifluoromethyl)quinolines 3 by reduction, 4-trifluoromethyl-2-quinolinecarboxylic acids 4 by permutational halogen/metal exchange followed by carboxylation, and 2-bromo-4-trifluoromethyl-3-quinolinecarboxylic acids 5 by consecutive treatment with lithium diisopropylamide and dry ice. Debromination of acids 5 makes 4-trifluoromethyl-3-quinolinecarboxylic acids 6 available. As at any time 2-trifluoromethyl-4-quinolinones 9 may form instead of the expected isomers 1, the structures have to be assigned on the basis of unequivocal NMR spectral criteria. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).