- Acid-Catalyzed Rearrangements of Vinylketene/Cyclopentadiene Adducts
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Vier Alkyl-vinylketene (7b-e), in situ durch 1,4-Eliminierung von HCl aus den entsprechenden α,β-ungesaettigten Acylchloriden hergestellt, wurden mit Cyclopentadien umgesetzt.Durch -Cycloaddition entstanden 7-alkyl-7-vinylsubstituierte Bicyclohept-2-en-6-one 8/9.Das Stereoisomerenverhaeltnis 8:9 haengt von der relativen Groesse der Ketensubstituenten ab.Die Vinylketen/Cyclopentadien-Addukte 8/9 enthalten ein α-Vinylcyclobutanon-, ein Cope- und (bei 8f) ein Allylchlorid-System.Unter dem Einfluss von Saeuren (meistens BF3-Aetherat) wurden bei 8/9 vier verschiedene Typen von Umlagerungsreaktionen beobachtet, naemlich, je nach dem Substitutionsmuster: -Alkyl-Wanderung zu Bicyclononadienonen 12, -Acyl-Wanderung zu Bicyclooctenonen 13, -Cope-Umlagerung zu Bicyclononadienonen 14 oder -Halogen-Wanderung zu 7-Alkylidenbicycloheptenonen 15.Die -Alkyl- und -Acyl-Wanderungen konkurrieren mit der Cope-Umlagerung, wobei auch die Konfiguration an C(7) der Vinylketen/Cyclopentadien-Addukte (8 bzw.9) und das Loesungsmittel eine Rolle spielen koennen.
- Huston, Rima,Rey, Max,Dreiding, Andre S.
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- Synthetic application of alkyl (E)-2-tributylstannyl-2-alkenoates: Selective synthesis of (S)-1-methylbutyl (E)-2-methyl-2-pentenoate, an aggregation pheromone component of Rhyzopertha dominica and Prostephanus truncatus
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Stereoisomerically pure (S)-1-methylbutyl (E)-2-methyl-2-pentenoate (dominicalure-1), (S)(E)-11, an aggregation pheromone component for the lesser and the greater grain borers, has been efficiently synthesized from the main product of the palladium-catalyzed reaction between ethyl 2-pentynoate, 1a, and Bu3SnH, i.e. ethyl (E)-2-tributylstannyl-2-pentenoate, (E)-2a.
- Rossi,Carpita,Cossi
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- Ene-diene transmissive cycloaddition reactions with singlet oxygen: The vinylogous gem effect and its use for polyoxyfunctionalization of dienes
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The singlet oxygen reactivities and regioselectivities of the model compounds 1b-d were compared with those of the geminal (gem) selectivity model ethyl tiglate (1a). The kinetic cis effect is kE/kZ = 5.2 for the tiglate/angelate system 1a/1a′ without a change in the high gem regioselectivity. Further conjugation to vinyl groups enabled mode-selective processes, namely, [4 + 2] cycloadditions versus ene reactions. The site-specific effects of methylation on the mode selectivity and the regioselectivity of the ene reaction were studied for dienes 1e-g. A vinylogous gem effect was observed for the γ,δ-dimethylated and α,γ,δ-trimethylated substrates 1h and 1i, respectively. The corresponding phenylated substrates 1j-l showed similar mode selectivity, as monomethylated 1j exhibited exclusively [4 + 2] reactivity while the tandem products 12 and 14 were isolated from the di- and trimethylated substrates 1k and 1l, respectively. The vinylogous gem effect favors the formation of 1,3-dienes from the substrates, and thus, secondary singlet oxygen addition was observed to give hydroperoxy-1,2-dioxenes 19 and 20 in an ene-diene transmissive cycloaddition sequence. These products were reduced to give alcohols (16, 17, and 18) or furans (24 and 25), respectively, or treated with titanium(IV) alkoxides to give the epoxy alcohols 26 and 27. The vinylogous gem effect is rationalized by DFT calculations showing that biradicals are the low-energy intermediates and that no reaction path bifurcations compete.
- Eske, Angelika,Goldfuss, Bernd,Griesbeck, Axel G.,De Kiff, Alan,Kleczka, Margarethe,Leven, Matthias,Neudoerfl, Joerg-M.,Vollmer, Moritz
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p. 1818 - 1829
(2014/03/21)
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- Highly enantioselective iridium-catalyzed hydrogenation of α,β-unsaturated esters
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α,β-Unsaturated esters have been employed as substrates in iridium-catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic- and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. Asymmetric hydrogenation: A variety of α,β-unsaturated esters were hydrogenated with high enantioselectivities (see scheme). The hydrogenated products have been used in synthetic transformations as well as in formal total syntheses. Copyright
- Li, Jia-Qi,Quan, Xu,Andersson, Pher G.
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supporting information
p. 10609 - 10616
(2012/11/07)
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- Rh-catalyzed asymmetric hydroformylation of functionalized 1,1-disubstituted olefins
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The first method for the highly enantioselective rhodium-catalyzed hydroformylation of 1,1-disubstituted olefins has been developed. By employing either of the P-chirogenic phosphine ligands BenzP* and QuinoxP*, linear aldehydes with β-chirality can be prepared in a highly enantioselective fashion with good chemo- and regioselectivities.
- Wang, Xiao,Buchwald, Stephen L.
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supporting information; experimental part
p. 19080 - 19083
(2012/01/05)
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- Palladium-catalyzed γ-arylation of α,β-unsaturated esters from silyl ketene acetals
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(Figure Presented) Smarty cat: A method for the palladiumcatalyzed γ-arylation of α,β-unsaturated esters via silyl ketene acetals in the absence of fluoride has been developed. The coupling proceeds with electron-rich and electron-poor aryl bromides and vinyl bromides in high yields with a high tolerance for other functional groups.
- Huang, David S.,Hartwig, John F.
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supporting information; experimental part
p. 5757 - 5761
(2010/11/02)
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- Stereoselective formal total synthesis of (+)-methynolide
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(Chemical Equation Presented) A highly stereoselective and convergent formal total synthesis of (+)-methynolide is described. The salient features of this synthesis have been the construction of the C1-C7 and C8-C11fragments via a desymmetrization approach, Sharpless asymmetric epoxidation of an allyl alcohol, respectively, and linkage of both the fragments by Nozaki-Hiyama-Kishi reaction.
- Yadav,Pratap,Rajender
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p. 5882 - 5885
(2008/02/09)
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- A formal stereoselective synthesis of (-)-maurenone
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An efficient formal synthesis of marine polypropionate (-)-maurenone is described. Highlights of the strategy include the utilization of a desymmetrization technique and the activation of the epoxide oxygen with a silyl triflate followed by intramolecular hydride transfer - a novel transformation. Georg Thieme Verlag Stuttgart.
- Yadav,Ravindar,Reddy
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p. 1957 - 1959
(2008/03/28)
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- Total Synthesis of Preaurovertin, Putative Biogenetic Precursor of Aurovertin. Biosynthetic Interrelationships between the Aurovertins, Citreoviridinols and Asteltoxin
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A number of complementary biomimetic approaches to the tetrahydrofuranyl portion of the dienal 13, which was used in a synthesis of preaurovertin, are described.Epoxidation of the trienoate 31 produces largely the β-epoxide 32, which on treatment with aqueous trifluoroacetic acid undergoes deacetalisation and concomitant cyclisation leading to compound 34.After conversion of 34 into dienal 13, a Wittig reaction with the ylide derived from the phosphonium salt 37 produces preaurovertin.Preaurovertin is a putative biogenetic precursor of aurovertin found in Calcarisporium arbuscula.Citreoviridin produced by Penicillium citreoviride relates to preaurovertin, and the citreoviridinols are related structurally to aurovertin.In addition, aurovertin is related biogenetically to asteltoxin found in Aspergillus stellatus.These structural and biosynthetic interrelationships are considered alongside the synthetic work.
- Forbes, Judith E.,Pattenden, Gerald
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p. 1959 - 1966
(2007/10/02)
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- Preparation et etude de nouveaux derives organozinciques allyliques fonctionnels
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Stable organozinc compounds derived from alkyl-3-alkyl-2-(bromomethyl)-propenoates have been prepared.NMR 13C, 1H and IR studies show only one Z stereoisomer (no methylenic form) with a strong chelation between zinc and the carbonyl oxygen of the ester and solvated by only one solvent molecule.Hydrolysis can be achieved by two concurrent mechanisms with or without transposition.
- Lambert, Francois,Kirschleger, Bernard,Villieras, Jean
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p. 273 - 286
(2007/10/02)
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- Studies on the Intramolecular Claisen Condensation. Stereospecific Ring-closure of β-Acetyloxy Esters
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On treatment with lithium bis(trimethylsilyl)amide, α-alkyl-β-acetyloxy esters (2) and (3) undergo stereospecific ring-closure to the 5,6-dihydro-4-hydroxy-2H-pyran-2-ones (2,4-dioxotetrahydropyrans) (4) and (5).
- Brandaenge, Svante,Leijonmarck, Hans
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p. 1097 - 1098
(2007/10/02)
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