Study on the synthesis of flavonols by radical C–H arylation of 3-hydroxychromone derivatives

The synthesis of flavonols by radical C-H-arylation of 3hydroxychromones was investigated. The use of diazonium salts in a photoredox process emerged as the most efficient approach, bypassing the need for prior in situ oxidation. When using phenylhydrazine or aniline derivatives as starting materials, yields were lower. Notably, neither 3-unsubstituted chromones nor 3-methoxychromones reacted.The natural product fisetin was obtained conveniently in four steps from 2-hydroxy-4-methoxyacetophenone.