Synthetic experiments in the benzopyrone series

Summary

The method of demethylation using aluminium chloride in benzene medium is shown to be applicable to polymethoxy flavanones. 5∶7∶4′-, 5∶7∶8- and 5∶6∶7-trimethoxy flavanones yield the corresponding trihydroxy compounds. Similarly carthamidin and isocarthamidin are obtained from their tetramethyl ethers whose synthesis is described. This work provides synthetic confirmation of the constitution of these tetrahydroxy flavanones proposed by Kuroda. That no isomeric change takes place in the preparation of carthamidin is established by its methylation to its tetramethyl ether.