6-Methoxy-2-oxo-1,2-dihydroquinoline-3,4-dicarbonitriles, A Red Compound Class with Solvent and pH Independent Green Fluorescence Maxima

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 (λexc 460 nm and λem 545 nm). This is remarkable, because starting carbostyrils 8, 16, 18, and 23 had a chloro substituent, a nitro substituent, an acetylamino substituent, or 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 substituent, an acetylamino substituent, 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.