Synthesis and Antimicrobial Evaluation of New Pyrano[4,3‐ b ]pyran and Pyrano[3,2‐ c ]chromene Derivatives Bearing a 2‐Thiophenoxyquinoline Nucleus

A new series of pyrano[4,3‐ b ]pyran 4a–i and pyrano[3,2‐ c ]chromene 6a–r derivatives bearing a 2‐thiophenoxyquinoline nucleus were synthesized by reaction of 2‐(4‐(un)‐substituted thiophenoxy)quinoline‐3‐carbaldehydes 2a–i with 6‐methyl‐4‐hydroxypyran‐2‐one 3 and 4‐hydroxy‐6‐(un)‐substituted‐2 H ‐chromen‐2‐one 5a–b respectively and malononitrile at room temperature in the presence of KOH as a basic catalyst. All the compounds were screened against three Gram‐positive bacteria ( Streptococcus pneumoniae , Bacillus subtilis , Clostridium tetani ), three Gram‐negative bacteria ( Salmonella typhi , Escherichia coli , Vibrio cholerae ) and two fungi ( Candida albicans , Aspergillus fumigatus ) using the broth microdilution MIC (minimum inhibitory concentration) method. Upon antimicrobial screening, it was observed that the majority of the compounds were found to be active against Bacillus subtilis , Clostridium tetani and Candida albicans as compared to standard drugs.