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- Dorange, Ismet, et al.
(författare)
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Allenes as carbon nucleophiles in intramolecular attack on (pi-1,3-diene)palladium complexes : Evidence for trans carbopalladation of the 1,3-diene
- 2003
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 9:14, s. 3445-3449
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of allene-substituted cyclohexa- and cyclohepta-1,3-dienes with [PdCl2(PhCN)(2)] gave eta(3)-( 1,2,3)-cyclohexenyl- and eta(3)-(1,2,3)-cycloheptenylpalladium complexes. respectively. in which C-C bond formation between the allene and the 1.3-diene has occurred. Analysis of the (pi-allyl)palladium complexes by NMR spectroscopy. using reporter ligands, shows that the C-C bond formation has occurred by a trans carbopalladation involving nucleophilic attack by the middle carbon atom of the allene on a (pi-diene)palladium(n) complex. The stereochemistry of the (pi-allyl)palladium complexes was confirmed by benzoquinone-induced stereoselective transformations to allylic acetates.
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| 4. |
- Närhi, Katja, et al.
(författare)
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An unexpectedly mild thermal alder-ene-type cyclization of enallenes
- 2006
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 71:7, s. 2914-2917
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Tidskriftsartikel (refereegranskat)abstract
- A mild, thermal Alder-ene reaction of enallenes has been developed. The allenic double bond acts as the "ene" and generates a carbon-carbon bond to an unactivated olefinic "enophile" in DMF at 120 degrees C to give [n.3.0] bicyclic systems (n = 3-5) in good yields. Except for a minor [2 + 2] cycloaddition byproduct, the reaction proceeded with complete atom economy, as there is no requirement of a catalyst or additional reactants, and no waste products are formed in the process.
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| 5. |
- Närhi, Katja, et al.
(författare)
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Palladium(0)-catalyzed cycloisomerization of enallenes
- 2005
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 11:23, s. 6937-6943
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Tidskriftsartikel (refereegranskat)abstract
- A novel palladium(0)-catalyzed cycloisomerization of enallenes has been developed. This reaction, catalyzed by [Pd(dba)(2)] (dba=dibenzylideneacetone) in acetic acid, results in the formation of cyclopentene derivatives and [n.3.0]bicyclic systems (n=3, 4) in good to high yields. The carbon-carbon bond-forming step is highly stereoselective to give cis-fused bicyclic systems. The presence of acetic acid as solvent and dba as ligand for palladium(0) turned out to be essential for the reaction in order to provide good reactivity and regioselectivity.
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| 8. |
- Närhi, Katja, 1976-
(författare)
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Studies on Palladium-Catalyzed Carbocyclizations of Allene-Substituted Olefins and 1,3-Dienes
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the development and mechanistic studies of carbocyclization reactions of allene-substituted olefins and 1,3-dienes, catalyzed by palladium(0) and palladium(II). These reactions results in the formation of [n,3,0] bicyclic systems (n = 3-5) with high stereoselectivity and in good to excellent yields. The first carbocyclization presented is a novel palladium(0)-catalyzed cyclo- isomerization of allene-substituted olefins. Secondly an efficient aerobic biomimetic system has been developed for a Pd(II)-catalyzed allylic oxidative carbocyclization of allene-substituted olefins. Additionally, during the studies of palladium-catalyzed carbocyclizations of allene-substituted olefins, it was found that in the absence of palladium a mild thermal ene-reaction occurs. In this manner stereodefined, functionalized bicyclic compounds are obtained with good regioselectivity and in high yields. The third and fourth carbocyclization developed are a palladium(II)-catalyzed oxidation and a palladium(0)-catalyzed intramolecular telomerization of allene-substituted 1,3-dienes. A mechanistic study of the palladium(II)-catalyzed oxidation of allene-substituted 1,3-dienes was made, and reaction intermediates could be isolated. The stereochemistry of the reaction intermediates was assigned, and this made it possible to suggest a mechanism for the reaction. The presented mechanism is a trans carbopalladation of the 1,3-diene, where the allene act as the carbon nucleophile. Due to different stereochemical outcomes of the stoichiometric and catalytic reactions, this mechanism could only explain the stoichiometric reaction. Another mechanism for the catalytic reaction was suggested, which rationalizes both the regio- and stereochemistry of the products.
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