Thermal cyclization of ethyl α-(2-chloro-2-propenyl)-β-arylaminocrotonates in mineral oil afforded the corresponding substituted 2,4-dimethylfuro[3,2-c]quinolines instead of the expected 4-hydroxy-2-methyl-3-(2-chloro-2-propenyl)quinolines. Scheme 1.

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New benzo-substituted 4-(aminophenylamino)-2-methylquinolines, 3-substituted 4-hydroxy(chloro and mercapto)quinolines, and thienoquinolines were synthesized. A model system based on oxidative damage to erythrocyte membranes induced by the combined actions of hydrogen peroxide and ionizing radiation was used to study the antihemolytic effects of these compounds as a means of assessing their antiradical/antioxidant properties. In the absence of x-rays, substances of the 3-substituted 4-hydroxy(chloro and mercapto)quinoline and thienoquinoline series were found to have marked antihemolytic effects, associated with significant influences on the structural stability of erythrocytes. However, with irradiation, the membrane-protecting effects were more marked with benzo-substituted 4-(aminophenylamino)-2-methylquinoline derivatives.

Synthesis was performed of substituted 2-methyl-4-quinoline thiouronium salts by reaction of 2-methyl-4-chloroquinolines with thiourea. The alkaline hydrolysis of these salts afforded the corresponding 2-methyl-4-quinolyl isothiocyanates and 2-methyl-4-mercaptoquinolines.We formerly reported on the new route of the alkaline hydrolysis of 2-methyl-4-quinoline thiouronium salts affording 2-methyl-4-quinolyl isothiocyanate [1]. In extension of this research we studied here the reaction with thiourea of 2-methyl-4-chloroquinolines containing in the benzene ring different (electron-donor and electronacceptor) substituents. The reaction occurred at heating the initial components in the ratio quinoline to thiourea equal to 1:1.1 in anhydrous acetone resulting in the quinolylthiouronium salts in a nearly quantitative yield.The alkaline hydrolysis of the salts obtained took two pathways: an intramolecular rearrangement analogous to Smiles rearrangement [25] affording the corresponding quinolyl isothiocyanates, and a bimolecular cleavage of a SC bond giving rise to substituted 2-methyl-4-mercaptoquinolines. The ratio of the final products depended on the character and the position of substituents, and from the 6-methoxy derivative the substitution product was not obtained at all. As expected, the electronic effects of substituents in positions 6 and 8 of the benzene ring were identical. The observed increase in the yield of rearrangement products in the systems under study in all likelihood is due to the existence of the molecule in a conformation most feasible for the rearrangement. This fact apparently governs the lack of compound IVc in the hydrolysis products of S-(2-methyl-6-methoxy-4-quinolyl)thiouronium chloride.

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