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 (λ_exc 460 nm and λ_em 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 .