Naturally occurring dibenzofurans. Part 3. On the structures of the rhodomyrtoxins
The degradation product of rhodomyrtoxin and ψ-rhodomyrtoxin, metabolites of the fruit of Rhodomyrtus macrocarpa Benth., previously assigned the structure 1,3,7,9-tetramethoxy-2,8-dimethyldibenzofuran (13) is now shown to be 1,3,7,9-tetramethoxy-4,6-dimethyldibenzofuran (15), the structure of this compound being determined by X-ray diffraction. By the synthesis of 1,1′-(1,3,7,9-tetrahydroxy-2,6-dimethyldibenzofuran-4,8-diyl)-3,3′-dimethyldibutan-1-one (17) and 1,1′-(1,3,7,9-tetrahydroxy-4,6-dimethyldibenzofuran-2,8-diyl)-2,3′-dimethyldibutan-1-one (2), structure (18), 1,1′-(1,3,7,9-tetrahydroxy-2,8-dimethyldibenzofuran-4,6-diyl)-3,3′-dimethyldibutan-1-one (18), is proposed for rhodomyrtoxin, and structure (1), 1,1′-(1,3,7,9-tetrahydroxy-2,8-dimethyldibenzofuran-4,6-diyl)-2,3′-dimethyldibutan-1-one (1), is confirmed for ψ-rhodomyrtoxin.