Articles written in Proceedings – Section A
Volume 36 Issue 4 October 1952 pp 231-243
Volume 37 Issue 5 May 1953 pp 620-628
For the preparation of flavanones having a 2′-methoxy group the acid method of chalkone condensation employing benzoates of hydroxy ketones is convenient. 5-Hydroxy-2′-methoxy flavanone and 5∶7-dihydroxy-2′-methoxy flavanone have thus been prepared. By demethylating the former with aluminium chloride 5∶2′-dihydroxy flavanone is obtained which undergoes only partial methylation in the 5-position even with excess of the reagent confirming that the 2′-hydroxyl is highly resistant. Synthetic 5∶7-hydroxy-2′-methoxy flavanone and its derivatives made by us and by Shinoda and Sato agree, but they do not agree in their properties with natural citronetin and its derivatives.
5-Hydroxy-2′-methoxy flavone does not undergo isomeric change under ordinary conditions of demethylation. 5∶2′-dihydroxy flavone undergoes partial methylation smoothly in the 2′-position thus showing the existence of marked difference between flavanones and flavones.
Volume 37 Issue 6 June 1953 pp 705-709
In their behaviour towards alkaline hydrogen peroxide 2′-methoxy chalkones behave normally and yield flavonols if the 6-position is free and benzalcoumaranones if this position has a methoxyl group. On the other hand 2′-hydroxy flavanones, and 5-hydroxy flavanones remain unaffected. This result is explicable on the basis that these hydroxy flavanone structures are stable and do not undergo change into the corresponding chalkone structures which alone suffer oxidation.