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À propos de : Shortcut Syntheses of Naturally Occurring 5-Alkylresorcinols withDNA-Cleaving Properties        

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  • Shortcut Syntheses of Naturally Occurring 5-Alkylresorcinols withDNA-Cleaving Properties
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  • Resorcinols such as 1−5 bearing longalkyl- or alkenyl substituents at the C-5 position,includingbola-formed bis-resorcinol derivatives, have recently been isolatedfrom natural sources and wereshown to exhibit exceptional DNA-cleaving properties under oxidativeconditions. Previous syntheticapproaches to such compounds seem inappropriately lengthy with regardto their structuralsimplicity. Disclosed is a very flexible synthesis which assemblesthese targets from triflate 7 andwell accessible alkenes, dienes, enynes, or dienynes, respectively, bymeans of a boron-mediatedreaction manifold. As a typical example,hexadeca-1,15-dien-8-yne 11 is hydroborated with9-H-9-BBN at all possible sites, the alkenyl borane entity of the resultingtris-borane 12 is selectivelycleaved off to afford the desired (Z)-alkene group in astereoselective manner, the remaining twoterminal alkylboranes are treated with NaOMe, and the bis-boratecomplex 13 thus formed is finallyused as the nucleophile for a palladium-catalyzed Suzuki cross-couplingreaction with triflate 7.This sequence is carried out in one pot and provides product14 in 62% overall yield. Demethylationof 14 (and analogues) can be conveniently achieved by meansof 9-iodo-9-BBN to afford the naturalproduct 5. The efficiency and flexibility of thisunprecedented approach which combines differentfeatures of classical and modern boron chemistry is furtherdemonstrated by the synthesis ofanacardic and ginkgolic acid derivatives.
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