Sodium hydride → (2-Hydroxy-5-carbomethoxy-benzoyl)-(2-methoxy-5-methyl-benzoyl)-methane

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A solution of methyl 3-acetyl-4-hydroxy-benzoate (6 g) and methyl 2-methoxy-5-methyl-benzoate (12 g) in dioxane (40 ml) was slowly added under stirring at room temperature to a suspension of sodium hydride 50% (4.5 g) in dioxane (40 ml). The mixture was kept under stirring for 3 hours at 80° C., cooled, then diluted with petroleum ether (100 ml), and filtered. The collected precipitate was dissolved in water, acidified with acetic acid and extracted with ethyl-acetate. The organic phase was washed with potassium carbonate 5% and water, then evaporated to dryness and crystallized from ethanol to give (2-hydroxy-5-carbomethoxy-benzoyl)-(2-methoxy-5-methyl-benzoyl)-methane (7.9 g; m.p.=145°-147° C.), which was then refluxed for 15 minutes with 99% formic acid (28 ml). After cooling and dilution in water and filtration, the collected precipitate was crystallized from acetone to obtain 6-carbomethoxy-2'-methoxy-5'-methyl-flavone (6 g), m.p.=154°-156° C., which was hydrolyzed with a 1% solution of potassium hydroxide (100 ml) in 95% ethanol at reflux temperature for 30 minutes. The mixture was cooled, acidified with 23% HCl to pH=3, and the precipitate was filtered, washed with ethanol 95% and water so obtaining, after crystallization from ethanol, 6-carboxy-2'-methoxy-5'-methyl-flavone (5.3 g), m.p.=246°-247° C.

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