5 : 6 : 7 : 8-hydroxyflavonols. Part II. A total synthesis

Abstract

A method of complete synthesis of 5 : 6 : 7 : 8-hydroxy flavonols is described. It starts from ω : 3 : 6-trimethoxy-2 : 4-dihydroxy-acetophenone which is subjected to partial methylation (of the 4-hydroxyl group) and subsequently to persulphate oxidation. The product, 2 : 5-dihydroxy-ω : 3 : 4 : 6-tetramethoxy-acetophenone is condensed with the anhydride and sodium salt of anisic acid and also of benzoic acid. The resulting 6-hydroxy-flavones yield on further methylation the fully methylated ethers of calycopteretin and 6 : 8-dihydroxy-galangin and on demethylation, the free hydroxy-flavonols.