An efficient one-pot synthesis of 4′-substituted flavones

A series of flavones were synthesized from 2-hydroxyacetophenones using a modified Baker-Venkataraman reaction. The 2-hydroxyacetophenone, 2,4-dihydroxyacetophenone, or 2,5-dihydroxyacetophenone, or 2,6-dihydroxyacetophenone was treated with 2 equiv of a 4-substituted aroyl chloride in 99:1 (w/w) acetone/water using both K2CO3 (8 equiv) and pyridine (4 equiv) as bases. Various 4'-substituted (R=H, Me, Cl, F) flavone derivatives were obtained via this one-pot procedure in high yield (>= 70%). This modified process is both simple and efficient. Compound 26b (3-(4-fluorobenzoyl)-5-hydroxy-4'-fluoroflavone) was synthesized for the first time with a yield of 12%. The method was unsuccessful, however, for the synthesis of one flavone, 5-hydroxy-4'-methoxyflavone.