- REACTIONS OF KETENE ACETALS 16. THE REGIOSPECIFIC SYNTHESIS OF PARTIALLY METHYLATED PURPURINS
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Two novel vinylketene acetals, 1,4-dimethoxy-1,3-bistrimethylsiloxybutadiene and 1,3,4-trimethoxy-1-trimethylsiloxybutadiene have been prepared in view of their eventual application to the synthesis of the antitumor antibiotic bikaverin.Use of the former in the elaboration of anthraquinones has shown that structures proposed for two natural products, purpurin 1-methyl ether and 8-hydroxypurpurin 1-methyl ether are in fact those of anthragallol derivatives.The second diene has afforded confirmation of the nature of xanthorin 5-methyl ether as well as of a degradation product of bostrycin.A substitution pattern claimed for another natural product, 5-hydroxyanthragallol 2,5-dimethyl ether, is also incorrect.
- Simoneau, Bruno,Brassard, Paul
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p. 3767 - 3774
(2007/10/02)
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- Reactions of Ketene Acetals. 13. Synthesis of Contiguously Trihydroxylated Naphto- and Anthraquinones
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A regiospecific method of obtaining various quinones bearing at least three adjacent hydroxyl groups has been devised by using a new vinylketene acetal, 2-methoxy-1,1,3-tris(trimethylsiloxy)-1,3-butadiene (9b).In this way the first total syntheses of dermoglaucin (50) and ceroalbolinic acid, as its pentamethyl derivative 49, have been achieved.The structure of another natural product, capareolatin dimethyl ether, was established indirectly by the unambiguous formation of one of the two possible isomers.Advantageous preparations of "7-hydroxyemodin", copareolatin, and isoerythrolaccin derivatives 32,38, and 2, as well as those of useful intermediates such as 2- and 3-chloro-5,7-dihydroxy-6-methoxynaphthoquinones or their dimethyl ethers, are described.
- Roberge, Guy,Brassard, Paul
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p. 4161 - 4166
(2007/10/02)
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