- Tandem reaction of 3-hydroxyhexa-4,5-allenic esters: A novel access to diversely substituted 2H-pyran-2-ones and indenes
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A highly efficient synthesis of diversely substituted 2H-pyran-2-ones and indenes through Bronsted acid promoted tandem reaction of the readily obtainable 3-hydroxyhexa-4,5-allenic esters under extremely mild conditions has been developed. The Royal Society of Chemistry 2012.
- Xu, Haiyun,Zhang, Xinying,He, Yan,Guo, Shenghai,Fan, Xuesen
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supporting information; experimental part
p. 3121 - 3123
(2012/04/18)
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- Tandem reactions of 1,2-allenic ketones leading to substituted benzenes and α,β-unsaturated nitriles
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One-pot double Michael addition/intramolecular aldol reaction/ decarboxylation of 1,2-allenic ketones with cyanoacetate offers an efficient and convenient approach to highly functionalized benzenes. With 2-substituted cyanoacetates, the reaction proceeds via a different tandem process to afford α,β-unsaturated nitriles effectively.
- Zhang, Xinying,Jia, Xuefei,Fang, Liangliang,Liu, Nan,Wang, Jianji,Fan, Xuesen
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supporting information; experimental part
p. 5024 - 5027
(2011/11/12)
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- Organocatalytic asymmetric conjugate addition to allenic esters and ketones
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The first example of an organocatalytic enantioselective conjugate addition of cyclic β-ketoesters and glycine imine derivatives to electron-deficient allenes is described. We disclose that the corresponding chiral β,γ-unsaturated carbonyl compounds are formed exclusively under phase-transfer conditions using either cinchona-alkaloid-derived or biphenyl-based chiral quaternary ammonium salts as catalysts. The scope of the reaction for β-ketoesters is outlined for allenes having a ketone or ester motif as electron-withdrawing group as well as different substituents in the 3-position, giving the optically active products in high yields and excellent diastereo- and enantioselectivities (90-96% ee). The conjugate addition also proceeds for a number of cyclic β-ketoesters having different ring sizes, ring systems, and substituents in high yields and enantioselectivities. Glycine imine derivatives also undergo the asymmetric conjugate addition to electron-deficient allenes in high yields and with enantioselectivities in the range of 60-88% ee, thus providing a rapid entry to optically active α-vinyl-substituted α-amino acid derivatives. It is shown that the enantioselectivity is strongly dependent on the size of the ester moiety of the nucleophile in combination with the catalytic system used. The high synthetic value of the chiral products arising from these new catalytic processes is demonstrated by two straightforward transformations leading in one case to optically active hexahydrobenzopyranones and in the other to substituted pyroglutamates (γ-lactames).
- Elsner, Petteri,Bernardi, Luca,Della Sala, Giorgio,Overgaard, Jacob,J?rgensen, Karl Anker
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p. 4897 - 4905
(2008/09/21)
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- A convenient and practical route to novel α-allenic ketones through a Wittig reaction
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A convenient synthesis of novel 5-arylpenta-3,4-diene-2-ones (3a-g) through a Wittig reaction of acetylmethylentriphenylphosphorane (2) with arylketenes is described.
- Kumar,Kaur,Ishar
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p. 1237 - 1238
(2007/10/03)
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- Enolates of α-allenyl ketones: Formation and aldol reactions of cumulenolates
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Enolization of α-allenyl ketones under kinetic conditions, followed by reactions with aldehydes and ketones, affords aldol products that suggest the intermediacy of cumulenolates, formed via the abstraction of a vinylic α-hydrogen. The origin for this marked difference with α-alkenyl ketones is attributed to the enhanced acidity of allenic hydrogens, to the predominance of the s-trans conformation, and to lithium complexation with both the carbonyl and the allene moieties. The relative stability of these enolates was examined with the use of semiempirical (MNDO) calculations which indicated that the lowest energy isomers are the (Z)-alkynolates. Both experimental and computational evidence suggest that the kinetic intermediate is the cumulenolate, while the thermodynamic enolate is the (Z)-alkynenolate.
- Petasis, Nicos A.,Teets, Kurt A.
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p. 10328 - 10334
(2007/10/02)
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- Thromboxane A2 Analogues from 8-Oxabicyclooct-6-en-3-ones
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We describe approaches to thromboxane A2 analogues (3), (4), and (32) which contain 2,6-dioxabicyclooctane and 2,6-dioxatricyclo3,7>nonane ring system.Both were derived from 2-substituted 8-oxabicyclooct-6-en-3-
- Bowers, Kevin G.,Mann, John,Walsh, E. Brian,Howarth, Oliver W.
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p. 1657 - 1666
(2007/10/02)
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