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| - syn-Oxidative Polycyclizations of Hydroxypolyenes: HighlyStereoselective and Potentially Biomimetic Syntheses ofall-trans-Polytetrahydrofurans
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| - Acylperrhenate reagents promote hydroxyl-directedsyn-oxidative polycyclizations of primary andsecondaryhydroxypolyenes, forming bis- and tristetrahydrofuranyl alcohols withexcellent trans-stereoselectivity for eachtetrahydrofuran ring. The combination ofdichloroacetylperrhenate/dichloroacetic anhydride affordsstereoselectivesyn-oxidative bicyclization to bistetrahydrofuranyl alcoholproducts, whereastrifluoroacetylperrhenate/trifluoroaceticanhydride or trichloroacetylperrhenate/trichloroacetic anhydride aremore suitable for stereoselective formation oftristetrahydrofuranyl alcohols from acyclic hydroxytrienes. In thetricyclization reaction chirality induction from asingle stereogenic hydroxyl group affords diastereoselective formationof six additional stereocenters in a singlestep. However, we have found that the growing polytetrahydrofuranchain can exert chelation effects upon thealkoxyrhenium intermediate, thus diminishing the degree of productdiastereoselectivity. These syn-oxidativecyclization synthesis strategies mimic a possible pathway for thebiosynthesis of many polycyclic ether natural products,including the tristetrahydrofuran acetogenin goniocin(1).
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