An efficient one-pot synthesis of flavones

Flavones were prepared using a one-pot procedure starting from the corresponding 2′-hydroxyacetophenones. The latter were treated with 3 equiv of aroyl chloride in wet K2CO3/acetone (1% w/w water) to afford a good yield of flavone and a smaller amount of 3-aroylflavone. Evidence was obtained that the reaction proceeds via a triketone intermediate. When the reactants were heated in 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and pyridine, the 3-aroylflavone was obtained exclusively. Use of a stoichiometric amount of aroyl chloride afforded only the corresponding flavone.