Articles written in Proceedings – Section A
Volume 37 Issue 1 January 1953 pp 104-113
A new method of synthesis of flavonols is described. It involves the oxiation of α-methoxy chalkones with alkaline hydrogen peroxide. The special advantages are (1) it avoids the formation of benzal coumaranones and (2) it gives good yields owing to the stability to further oxidation conferred by the 3-methoxyl group. The same products are obtained using selenium dioxide as the oxidising agent. Complete methyl ethers of galangin and kæmpferol have been prepared. The method is also useful for the preparation of partial methyl ethers of flavonols. 3∶5∶7∶4′-Tetramethyl ether of quercetin and 3∶5∶7-trimethyl ether of quercetin are prepared. The former has been subjected to partial demethylation to yield the new 7∶4′-dimethyl ether of quercetin which is now named isorhamnazin.
Under ordinary conditions 2-hydroxy-6-methoxy chalkone yields with alkaline hydrogen-peroxide only 4-methoxy benzalcoumaranone and not 5-methoxy flavonol as claimed by Oliverio and Schiavello.