A novel ferrocenyl diselenide for the catalytic asymmetric aryl transfer to aldehydes

Bolm, Carsten; Kesselgruber, Martin; Grenz, Achim; Hermanns, Nina; Hildebrand, Jens P.

doi:10.1039/b003237i

Cited by 67 publications

(27 citation statements)

References 16 publications

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“…The latter problem was addressed by Bolm and coworkers, who discovered that the mixed reagent EtZnPh33 exhibited a slower background reaction than diphenylzinc. EtZnPh also resulted in higher enantioselectivities with the same catalysts (Scheme 1B), in part from the reduced contribution of the background reaction 37-42. EtZnPh is easily generated by combining Ph 2 Zn and Et 2 Zn (Equation 1).…”

Section: Introductionmentioning

confidence: 99%

Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl Heteroaryl-, and Diheteroarylmethanols

2009

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Enantioenriched diaryl-, aryl heteroaryl-and diheteroarylmethanols exhibit important biological and medicinal properties. One-pot catalytic asymmetric syntheses of these compounds beginning from readily available aryl bromides are introduced. Thus, lithium-bromide exchange with commercially available aryl bromides and n-BuLi was followed by salt metathesis with ZnCl 2 to generate ArZnCl. A second equivalent of n-BuLi was added to form the mixed organozinc, ArZnBu. In the presence of enantioenriched amino alcohol-based catalysts, ArZnBu adds to aldehydes to afford essentially racemic diarylmethanols. The low enantioselectivities were attributed to a LiCl-promoted background reaction. To inhibit this background reaction, the chelating diamine TEEDA (tetraethylethylene diamine) was introduced prior to aldehyde addition. Under these conditions, enantioenriched diarylmethanols were obtained with >90% ee. Arylations of enals generated allylic alcohols with 81-90% ee. This procedure was unsuccessful, however, when applied to heteraryl bromides, which was attributed to decomposition of the heteroaryl lithium under the salt metathesis conditions. To avoid this problem, the metathesis was conducted with EtZnCl, which enabled the salt metathesis to proceed at low temperatures. The resulting EtZn(Ar Hetero ) intermediates (Ar Hetero =2-and 3-thiophenyl, 2-benzothiophenyl, 3-furyl, and 5-indolyl) were successfully added to aldehydes and heteroaryl aldehydes with enantioselectivities between 81-99%. These are the first examples of catalytic and highly enantioselective syntheses of diheteroarylmethanols. In a similar fashion, ferrocenyl bromide was used to generate FcZnEt and the ferrocenyl group added to benzaldehyde and heteroaromatic aldehydes to form ferrocene-based ligand precursors in 86-95% yield with 96-98% ee. It was also found that the arylation and heteroarylation of enals could be followed by diastereoselective epoxidations to provide epoxy alcohols with high enantio-and diastereoselectivities in a one-pot procedure.

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Section: Introductionmentioning

confidence: 99%

Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl Heteroaryl-, and Diheteroarylmethanols

2009

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“…Steric effect research has seen major advances in the last decade, with important contributions from Exner's group. [1][2][3][4][5][6][7][8][9][10][11][12] This paper focuses on several aspects of the o-hydroxyaryl Schiff bases research. The paper focuses on the intramolecular hydrogen bond of the O-HÁ Á ÁN type which forms between the hydroxyl group of the phenol ring (the proton donor) and the nitrogen atom of the imine (the proton acceptor) (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Intramolecular hydrogen bonding in o‐hydroxyaryl Schiff bases

Filarowski

2005

J of Physical Organic Chem

121

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This review deals with selected aspects of research on o-hydroxyaryl Schiff bases. Special attention is given to results obtained by x-ray, IR, UV and NMR spectroscopic methods and quantum-mechanical calculations that allow a better understanding of the nature of o-hydroxyaryl Schiff bases. The paper reports on studies of sterically modified o-hydroxyaryl Schiff bases with an intramolecular hydrogen bond made short owing to steric repulsion. The following points are focused upon: structural and energetic analysis of the steric effect and its influence on the hydrogen bond length; proton localization and the proton transfer process; the impact of proton transfer on the chelate and phenol rings in the intramolecular hydrogen bond; a generalized scheme of tautomer equilibrium and its study with the use of experimental and theoretical methods; some discrepancies found in standard parameters for a particular tautomeric form; calculations of the potential energy curve for basic tautomer forms; influence of the steric effect on the potential curve shape; and a review of semi-empirical and quantum-mechanical calculations of molecular structures in the ground state.

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“…The activation barriers are not lowered by the introduction of ethyl groups (Table 1), and the observed reaction rate does not increase. [10] Furthermore, the computational results for the reagent pre-equilibrium, as well as tentative NMR spectroscopic assignment of the same equilibrium in THF, [10] indicates that Ph 2 Zn (required for the all-Ph path, Table 1, entry 8, and also for the background reaction) is still present in the reaction mixture after addition of a twofold excess of Et 2 Zn. This leaves us with the last component of the reaction, the catalyst formed from deprotonated ligand 1 and RZn.…”

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confidence: 96%

“…Thus, all three R 2 Zn complexes will be present in the reaction mixture, in agreement with the observation by NMR spectroscopy of formation of an additional Ph-Zn moiety on addition of Et 2 Zn to Ph 2 Zn. [10] Fast exchange of R groups is expected from the crystal structure of the Ph 2 Zn dimer, [18] so that R 2 Zn can be assumed to be present as a statistical mixture (CurtinHammett conditions). [19] Looking more closely at the possible paths for the reagent mixture reveals that the highest reactivity is obtained with the pure phenyl system, in perfect agreement with the observation of higher reactivity in the absence of Et 2 Zn.…”

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confidence: 99%

Phenyl versus Ethyl Transfer in the Addition of Organozinc Reagents to Aldehydes: A Theoretical Study

et al. 2003

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A novel ferrocenyl diselenide for the catalytic asymmetric aryl transfer to aldehydes

Cited by 67 publications

References 16 publications

Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl Heteroaryl-, and Diheteroarylmethanols

Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl Heteroaryl-, and Diheteroarylmethanols

Intramolecular hydrogen bonding in o‐hydroxyaryl Schiff bases

Phenyl versus Ethyl Transfer in the Addition of Organozinc Reagents to Aldehydes: A Theoretical Study

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