Formation of quinones by oxidative demethylation

Summary

Two isomers of methyl pedicinin are synthesised and studied: (1) 4: 7-dihydroxy-5: 6-dimethoxy-benzal-coumaranone and (2) 5: 6-dimethoxy-4: 7-quino-benzyl-coumaranone. The first is made from 2-hydroxy-3: 4: 5: 6-tetramethoxy-chalkone by conversion into the corresponding benzal-coumaranone, oxidative demethylation to 4: 7-quinone and reduction to the quinol. The second synthesis condenses pentamethoxy-benzene with α-bromo-β-phenyl-propionyl chloride to yield tetramethoxy-benzyl-coumaranone and oxidises it with nitric acid to the quinone. Their properties are different from methyl pedicinin and they do not undergo conversion into it. It is therefore concluded that methyl pedicinin should be given only the quinone chalkone formula and that the alternative formulations are not valid. Further the possibility of reversible isomeric change between chalkones and benzylcoumaranones does not find experimental support.