Synthetical experiments in the chromone group-part XXIII. A new synthesis of rhamnazin and a synthesis of 3: 4'-dihydroxy-7-methoxyflavone

Abstract

The Algar-Flynn oxidation ofo′-hydroxychalkones to flavonols by means of alkaline hydrogen peroxide is applicable to chalkones with a hydroxyl group in the 4-position, irrespective of the presence of a methoxyl group in the 6′-position. Rhamnazin 5-methyl ether, and rhamnazin by partial demethylation with aluminium chloride, have thus been synthesized. Geissman and Fukushima have shown that 2′-hydroxy-6′-methoxychalkones give benzalcoumaranones, the flavonols not being formed or only as minor products. The influence of the 4-hydroxyl group on the course of the reaction is discussed.