Synthetic experiments in the benzo-pyrone series

Summary

By the action of aluminium chloride on karanjin using nitrobenzene as solvent, smooth conversion into karanjonol could be effected. When benzene is used instead, besides demethylation a molecule of benzene adds on to yield α-phenyl-α: β-dihydro-karanjonol. Similar addition takes place in the case of toluene also. That the double-bond of the furan ring is involved in this reaction has been established by studying the behaviour of a few similar flavone compounds under the same conditions. It has been incidentally shown that a methyl ether group in the 3-position is readily affected in nitrobenzene solution whereas in the 7-position it is stable and the preparation of 7-methoxy-flavonol is easily carried out by demethylation of 3: 7-dimethoxy-flavone.