The sodium p-toluenesulfinate mediated reaction of potassium cyanide with 4-chlorocarbostyrils 8, 16, 18 and 23 gave in all cases the highly fluorescent and stable 6-methoxy-2-oxoquinoline-3,4-dicarbonitrile 9 (exc 460 nm and em 545 nm). This is remarkable, since starting carbostyrils 8, 16, 18 and 23 had a chloro-, a nitro-, an acetylamino- and a piperidinyl substituent in position 3. Hence we observed not only a substitution of the 4-chloro and expected 3-chloro substituents by the cyanide nucleophile but also an exchange of a nitro-, an acetylamino- and a piperidinyl substituent in position 3. The multistep insertion of substituents leading to 8, 16, 18 and 23 started from 4-hydroxy-6-methoxyquinolone 4, easily obtained from p-anisidine and malonic acid. Substitutions in position 3 gave 4-hydroxy-3-nitro and -3-chloro intermediates, which were converted to 3,4-dichlorocarbostyril 8 and 4-chloro-3-nitrocarbostyril 16. Reduction of the 3-nitro intermediate led to the 3-acetylamino analog and subsequent chlorination led to 3-acetylamino-4-chlorocarbostyril 18. 4-Chloro-3-piperidinylcarbostyril 23 was obtained from intermediate 3,3-dichloroquinolinedione by subsequent amination, reduction and chlorination. Further, 3-acetylamino-4-chlorocarbostyril 18 gave with lithium p-toluenesulfinate highly fluorescent 3-amino-6-methoxy-4-p-tolylsulfonylquinolone 19.
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