- Effective chiral ferrocenyl phosphine-thioether ligands in enantioselective palladium-catalyzed allylic alkylations
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Chiral ferrocene-derived phosphine-thioether mixed donor ligands supported by heterocycles effected the palladium-catalyzed enantioselective allylic alkylations with excellent yields and enantioselectivities (up to 96% ee). With cyclic and unsymmetrical a
- Cheung, Hong Yee,Yu, Wing-Yiu,Au-Yeung, Terry T. L.,Zhou, Zhongyuan,Chan, Albert S. C.
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- Studies on the Enantioselectivity in Bu4N-Catalyzed Nucleophilic Substitution of Optically Active Allylic Carbonates with Malonate
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The stereochemical outcomes of optically active allylic carbonates 2, 5, and 9 with malonate in the presence of iron catalyst 1 were determined.It was found that in every case the nucleophile predominantly attacked at the carbon atom where the leaving group was attached, and the corresponding prevailing regioisomer 3, 6, or 10 was obtained with high retention of configuration at the chiral center.
- Zhou, Bo,Xu, Yuanyao
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- Palladium-catalyzed enantioselective allylic substitution in the presence of monodentate furanoside phosphoramidites
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A library of monodentate furanoside phosphoramidites, easily synthesized from inexpensive D-xylose and optically pure 1,1-bi-2-naphthol (BINOL), was used as ligands for the palladium-catalyzed allylic alkylation and amination. The matched pair was formed from D-xylose-derivatives and (S)-BINOL. The asymmetric induction depends strongly on the substituent at the C5 of the carbohydrate backbone; both bulky 5-O-pivaloyl and 5-deoxy derivatives gave excellent results, whereas ligands with trityl protection at position C5 induced low ee values with reversal of configuration. The solvent used for the addition is also of great importance with highest enantioselectivities observed in diethyl ether. The best results for both alkylation and amination, up to 98-99 ee, were obtained for sterically demanding allylic acetates. Single is better: New carbohydrate ligands bearing a single 1,1-bi-2-naphthol (BINOL)-derived phosphoramidite moiety are developed and successfully applied to the palladium-catalyzed asymmetric allylic substitution. The enantioselectivities are equal or better than those obtained for similar systems containing two BINOL moieties and reach up to 99 ee.
- Majdecki, Maciej,Jurczak, Janusz,Bauer, Tomasz
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p. 799 - 807
(2015/03/14)
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- Enantioselective allylic alkylation catalyzed by novel C2-symmetric bisphosphinites
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In this article, we present our results concerning new C2-symmetric bisphosphinites with a (1R,2R)-1,2-bis([1,1: 3,1-terphenyl]-5-yl)ethane backbone. For the given chirality of the backbone, derivatives with aromatic and aliphatic substituents
- G?k, Ya?ar,Zeki G?k, Halil
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p. 490 - 495
(2015/04/27)
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- Highly diastereoselective synthesis of 2,6-di[1-(2-alkylaziridin-1-yl) alkyl]pyridines, useful ligands in palladium-catalyzed asymmetric allylic alkylation
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C2-Symmetrical, enantiopure 2,6-di[1-(1-aziridinyl)alkyl] pyridines (DIAZAPs) were prepared by a high-yielding, three-step sequence starting from 2,6-pyridinedicarbaldehyde and (S)-valinol or (S)-phenylglycinol. The new compounds were tested as
- Savoia, Diego,Alvaro, Giuseppe,Di Fabio, Romano,Fiorelli, Claudio,Gualandi, Andrea,Monari, Magda,Piccinelli, Fabio
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p. 1883 - 1893
(2007/10/03)
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- Palladium complexes with chiral diphospholane ligands: Comparative catalytic properties and analysis of (η3-allyl)palladium species
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The chiral diphospholane ligands Duphos (1) and Duxantphos (2), which can be differentiated by their bite angle, were applied to palladium-catalysed asymmetric reactions, essentially allylic alkylations with symmetrically (3a-d) or unsymmetrically (5a,b) substituted allylic acetates as substrates. The most interesting results were found with the first series of substrates in which 2 was more reactive and/or selective than 1. The model complexes of the catalytic intermediates [Pd{(S,S)-1}(η3-cyclohexenyl)](BF4) (10) and exo-[Pd{(R,R)-(η3-cyclohexenyl)](SbF6) (11) could be characterised by X-ray crystallography. 1H and 32P NMR spectroscopic analyses of [Pd{(R,R)-2}(η3-diphenylallyl)] (SbF6) (12) and [Pd{(R,R)-2}(η3-allyl)](SbF 6) (13) revealed the presence of exchanging isomers in solution. Structural data provided by these techniques combined with the preferential rotation model led to a satisfactory interpretation of the catalytic allylic alkylation results. It appears that the bite angle plays a crucial role in the positioning of the proximal methyl groups, which determines the distribution of allyl isomeric intermediates and the balance between clockwise and anticlockwise rotations in the enantioselective step. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Malaise, Gregory,Ramdeehul, Shailesh,Osborn, John A.,Barloy, Laurent,Kyritsakas, Nathalie,Graff, Roland
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p. 3987 - 4001
(2007/10/03)
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- Molecular mechanics predictions and experimental testing of asymmetric palladium-catalyzed allylation reactions using new chiral phenanthroline ligands
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Molecular mechanics calculations were used to probe the conformational properties of a number of substituted phenanthrolines and their η3- allylpalladium complexes. Special attention was focused on phenanthrolines bearing chiral, terpene-derived, alkyl and alkenyl groups at C(2). Based upon these calculations, predictions could then be made regarding the suitability of the several ligands for use in asymmetric palladium-catalyzed substitution reactions of allylic acetates. Each of the substituted phenanthrolines was prepared by straightforward means. Use of these ligands in catalytic allylations gave results which were in good agreement with the calculation- based predictions. The highest levels of asymmetric induction were predicted and were obtained with a readily available 2-(2-bornyl)phenanthroline ligand 13. The results were compared with previously reported data obtained using other ligands. Overall, this work provides further indication of the potential utility of a combined calculational/experimental approach for the design of chiral catalysts.
- Pe?a-Cabrera, Eduarde,Norrby, Per-Ola,Sj?gren, Magnus,Vitagliano, Aldo,De Felice, Vineenzo,Oslob, Johan,Ishii, Sbingo,O'Neill, David,?kermark, Bj?rn,Helquist, Paul
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p. 4299 - 4313
(2007/10/03)
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- Asymmetric Allylic Alkylation Catalyzed by Palladium-Sparteine Complexes
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The cationic complex 3-C3H5)(sparteine)>PF6 (6) was found to be a suitable catalyst precursor for the asymmetric alkylation of allylic acetates with Na as the nucleophile.This constitutes one of the first and still rare examples of a phosphine-free system for this type of Pd-catalyzed reaction.Using 5 mol percent of 6, alkylation products were obtained in up to 90 percent isolated yield and 85 percent enantiomeric excess.The alkylation reaction was shown to occur with overall retention of configuration, indicating an analogous mechanism to the one previouslyproposed for phosphine-containing catalysts.The reactivity of allylic acetates is strongly dependent upon the nature of the substituents, open-chain aliphatic substrates being unreactive.
- Togni, Antonio
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p. 683 - 690
(2007/10/02)
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