Synthesis and antibacterial activity of 2‐phenyl‐4 H ‐benzo[ b ]thiopyran‐4‐ones (Thioflavones) and related compounds

A number of 2‐phenyl‐4 H ‐benzo[ b ]thiopyran‐4‐ones (thioflavones) and related compounds have been prepared to test their antibacterial activity. The flavone derivatives were also prepared to compare with their antibacterial activity. It was found that hydroxythioflavones were easily prepared by demethylation of methoxythioflavones with aluminium chloride. In the test of antimicrobial activity, methoxy‐ or hydroxythioflavones were found to be inactive. It is suggested that the sulfone or sulfoxide of thioflavone is required for antimicrobial activities against yeast funguses and molds. These thioflavone derivatives exhibit low acute toxicity.