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By using the method of Allan-Robinson’s flavone synthesis, the condensation of 3,ω-dimethoxy-2,1,6-trihydroxyacetophenone with 3,4-dibenzyloxybenzoic anhydride gave a mixture of 3,6- and 3,8-dimethoxy-3′,4′-dibenzyloxy-5,7-dihydroxyflavone (X and XI). The catalytic debenzylation of the above flavones then gave axillarin (I) and 3,8-dimethoxy-5,7,3′,4′-tetra-hydroxyflavone (IV) respectively. Axillarin 7-O-methyl ether(III) was prepared by the partial methylation of X, followed by catalytic debenzylation.

The partial benzylation of 3-methoxy-2,4,6-trihydroxyacetophenone gave a mixture of 2,4-dibenzyloxy-6-hydroxy- and 4,6-dibenzyloxy-2-hydroxy-3-methoxyacetophenone. The latter was esterified with 4-benzyloxy-3-methoxybenzoyl chloride, and the resulting ester was converted into 8,3′-dimethoxy-5,7,4′-tribenzyloxyflavone via the corresponding diketone. The catalytic debenzylation of the flavone gave 8,3′-dimethoxy-5,7,4′-trihydroxyflavone. Its diethyl ether was also prepared from 3,6-dimethoxy-4-ethoxy-2-hydroxyacetophenone by an unambiguous method.

The Hoesch reaction of iretol with methoxyacetonitrile yielded 2,4,6-trihydroxy-3,ω-dimethoxyacetophenone. According to the Allan-Robinson flavone synthesis with O-benzylvanillic anhydride, the acetophenone afforded 4′-benzyloxy-5,7-dihydroxy-3,3′,6-trimethoxyflavone. The catalytic debenzylation of the flavone gave jaceidin, 4′,5,7-trihydroxy-3,3′,6-trimethoxyflavone, which had previously been isolated from Centaurea species. Its triethyl ether was prepared from 3,5-diethoxy-4-methoxyphenol via the corresponding acetophenone, followed by the abovementioned flavone synthesis with O-ethylvanillic anhydride. The ultraviolet spectra of these flavones will also be reported.

The acid-catalyzed isomerization of 4-benzyloxy-2′-hydroxy-3,4′,5′,6′-tetramethoxychalcone gave 4′-benzyloxy-3′,5,6,7-tetramethoxyflavanone, which was then converted by oxidation to 4′-benzyloxy-3-hydroxy-3′,5,6,7-tetramethoxyflavone. This, after debenzylation to 3,4′-dihydroxy-3′,5,6,7-tetramethoxyflavone, was partially demethylated with aluminum chloride or aniline hydrochloride to give 3,4′,5-trihydroxy-3′,6,7-trimethoxyflavone (I) (mp 213–214°C), the structure proposed previously for the chrysosplenetin (mp 177–178°C) isolated from Chrysosplenium japonicum Makino. However, the synthetic flavone was found to be different from natural chrysosplenetin by a mixed melting point determination and by a comparison of the spectra. Finally, the structures of chrysosplenetin and chrysosplenin were established by the spectroscopic studies to be 4′,5-dihydroxy-3,3′,6,7-tetramethoxyflavone (XIII) and its 4′-glucoside (XIV) respectively. The revised structure for chrysosplenetin has been fully confirmed by direct co...

2,4-Dibenzyloxy-6-hydroxy-3-methoxyacetophenone was esterified with 3,4-disubstituted benzoyl chlorides, and the resulting esters were converted into 7-benzyloxy-5-hydroxy-6-methoxyflavone derivatives via the corresponding diketones. The catalytic hydrogenolysis of the benzyloxyflavones gave the desired 5,7-dihydroxy-6-methoxyflavones. Ethyl ethers of these flavones were also prepared from 2,4-diethoxy-3-methoxy-6-hydroxyacetophenone by an unambiguous method. 6,3′-Dimethoxy-5,7,4′-trihydroxyflavone, desmethoxycentaureidin (6,4′-dimethoxy-5,7,3′-trihydroxyflavone), and 6-methoxyluteolin (6-methoxy-5,7,3′,4′-tetrahydroxyflavone) were thus prepared.