The synthesis of 6-R-2,2,4-trimethyl-1,2-dihydroquinoline- and 6-R-4-R’-2,2,4-trimethyl-1,2,3,4-tetrahydroquinoline-8-carboxylic acids – the structural analogues of helquinoline

S. M. Medvedeva, M. E. Plaksina, Kh. S. Shikhaliev


The peculiarities of the oxidation reaction of substituted (5,6-dihydro)-4,4,6-trimethyl-4H-pyrrolo[3,2,1-ij] quinoline-1,2-diones have been investigated. 6-R-2,2,4-trimethyl-1,2-dihydroquinoline-8-carboxylic acids and 6-R-4-R’-2,2,4-trimethyl-1,2,3,4-tetrahydroquinoline-8-carboxylic acids, which are structural analogues of the natural antibiotic Helquinoline ((2R,4S)-4-methoxy-2-methyl-1,2,3,4-tetrahydroquinoline-8-carboxylic acid), have been obtained by oxidation of 8-R-4,4,6-trimethyl-4H-pyrrolo[3,2,1-ij]quinoline-1,2-diones and their hydrogenated analogues – 8-R-6-R’-4,4,6-trimethyl-5,6-dihydro-4H-pyrrolo[3,2,1-ij]quinoline-1,2-diones. It has been shown that 8-R-6-R’-4,4,6-trimethyl-5,6-dihydro-4H-pyrrolo[3,2,1-ij]quinoline-1,2-diones and 8-R-4,4,6-trimethyl-4H-pyrrolo [3,2,1-ij]quinoline-1,2-diones are oxidized similar to isatin with opening of the pyrrole-1,2-dione fragment and subsequent decarboxylation, and the presence of bulky substituents – gem-dimethyl groups in the second position of the hydroquinoline cycle has no steric effect on the process. Moreover, it has been found that oxidation of 8-R-4,4,6-trimethyl-4H-pyrrolo[3,2,1-ij]quinoline-1,2-diones proceeds selectively with opening the pyrrole-1,2- dione fragment without affecting the multiple bond of the dihydroquinoline cycle, polymerization also does not occur on it. The structure of 6-R-4-R’-2,2,4-trimethyl-1,2,3,4-tetrahydroquinoline-8-carboxylic acids and 6-R-2,2,4-trimethyl-1,2-dihydroquinoline-8-carboxylic acids has been confirmed by 1H NMR and 13C NMR spectroscopy, mass spectrometry and elemental analysis. With the help of mass spectroscopy it has been shown that the heterocyclic fragment of 6-R-2,2,4-trimethyl-1,2-dihydroquinoline-8-carboxylic acids is more stable compared to the fragment of 6-R-4-R’-2 2,4-trimethyl-1,2,3,4-tetrahydroquinoline-8-carboxylic acids.


pyrrolo[3,2,1-ij]quinoline-1,2-diones; oxidation; 6-R-2,2,4-trimethyl-1,2-dihydroquinoline- 8-carboxylic acid; 6-R-4-R’-2,2,4-trimethyl-1,2,3,4-tetrahydroquinoline-8-carboxylic acid

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