Colouring Matters of Australian plants. 6. Haemocorin: The structure of the Aglycone.

Some model mono- and dihydroxyperinaphthenones have been prepared for comparison with the natural colouring matter. Their properties indicate that haemocorin is most probably a derivative of 2,5,6-trihydroxyperinaphthenone. In particular 6-hydroxy-7(or 9)-phenylperinaphthenone evidently includes the main features of the chromophore, but the extra oxygen substituents in the aglycone must have a strong auxochromic effect. The complete structure has been finally established by decarboxylation of the two dimethoxyphenylnaphthalic anhydrides previously obtained by oxidation of the isomeric dimethyl ethers. The products have been identified by synthesis as 1,2-dimethoxy-6-phenylnaphthalene and 1,2-dimethoxy-8-phenylnaphthalene. The aglycone is therefore formulated as 2,6-dihydroxy-5-methoxy-9-phenylperinaphthenone-l although this structure is potentially tautomeric.