O-Hydroxy-dibenzoylmethane

Method 1 is a new method for the direct production of flavone from o-benzoyloxy acetophenone and has been successfully applied to the synthesis of other flavones. Method 2, which involves the Baker-Venkataraman transformation, is recommended because of its high over-all yield and the reproducibility of the results. Mozingo and Adkins method 6 is satisfactory but the yield of o-hydroxy dibenzoylmethane is variable. 

A relevant neighbouring group participation was noted in the oxidative cyclization of o-hydroxy-acetophenone [23] and o-hydroxy-dibenzoylmethane. 

This type of reaction was first used by Dilthey and Fischer69 in connection with the mechanism of the type in Section II, D, 2. By analogy with the well-known formation of benzopyrylium salts from methyl(ene) ketones and o-hydroxybenzaldehyde or o-hydroxy-acetophenone,340 benzoylacetone (84, R = Me, R = H, R" = Ph) and acetophenone (85, RIV = Ph, R" = H) afforded in the presence of acetic anhydride and sulfuric acid, 2-methyl-4,6-diphenylpyrylium sulfoacetate. The interesting feature of this reaction is that a unique product is obtained (i.e., only the carbonyl group of the diketone adjacent to the phenyl enters the condensation, although two such groups are available) R and R" could be reversed, but they are not.69-69 Similarly, dibenzoylmethane (84, R = R" = Ph, R =H) afforded 2,4,6-triphenylpyrylium with acetophenone in 80% yield.69... 

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