Substituted quinolinones. 31. Some new pyrano[3,2-c]quinoline-3-carboxamides and their antioxidant activity

Abstract

Abstract 1‐Ethyl‐4‐hydroxy‐2‐oxo‐1,2‐dihydroquinoline‐3‐carbaldehyde (1) was annulated using malonic acid and/or its ethyl ester to furnish pyrano[3,2‐c]quinoline‐ 3‐carboxylic acid 2 and its ester 3. Interconversions between acid 2 and ester 3 were successfully carried out. The anticipated pyrano[3,2‐c]quinoline‐3‐ carboxamides 5–12 were conveniently attained via condensation of ester 3 with the proper amine. Surprisingly, treatment of ester 3 with dimethylformamide (DMF) in acidic media led to the carboxamide 5. All attempts to convert ester 3 to its corresponding acid hydrazides by interaction with the proper hydrazine derivative led to formation of pyrazolidinediones 15 and 17. Ester 3 underwent cyclo‐condensation with malononitrile dimer affording pyrido[3′,4′:5,6] pyrano[3,2‐c]quinoline derivative 18. The new compounds revealed significant antioxidant effect, which suggests that most of them are possible potent antioxidant agents. 1 |