Lise Meitner Minerva Center for Computational Quantum Chemistry

Haifa, Israel

Lise Meitner Minerva Center for Computational Quantum Chemistry

Haifa, Israel
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Mejuch T.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Gilboa N.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Gayon E.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Wang H.,University of California at Los Angeles | And 2 more authors.
Accounts of Chemical Research | Year: 2013

The reaction of a substituted allylmetal with a prostereogenic carbonyl compound can give rise to up to two racemic diastereomers (syn and anti). Classically, in such reactions, when pure E-isomers have afforded anti-selectivity and the Z-isomers exhibit syn-selectivity, researchers have used the empirical Zimmerman-Traxler model. In this model, chair-like transition states dominate over boat-like arrangements. The incoming aldehyde alkyl (aryl) residue occupies a pseudoequatorial rather than a pseudoaxial position to avoid potential 1,3-diaxial steric interactions. However, the reaction of γ,γ-disubstituted allylzinc species with carbonyl compounds generates two gauche interactions, which may result in a completely different stereochemical outcome. With these two gauche interactions, would a transition state in which the aldehyde substituent occupies a pseudoequatorial position or a pseudoaxial position be preferred?In this Account, we show that reaction of γ,γ-disubstituted allylzinc species with carbonyl compounds proceeds through a chair-like transition state and the substituent of the incoming aldehyde residue prefers to occupy a pseudoaxial position to avoid these two gauche interactions. Theoretical calculations on model systems support our experimental results. We have extended this new stereochemical outcome to describe the formation of α-alkoxyallylation of aldehydes through the formation of the rather uncommon (E)-γ,γ-disubstituted alkoxyallylzinc species. We also used this method to transform aromatic ketones and α-alkoxyaldehydes and ketones into functionalized adducts. In a one-pot reaction and using simple alkynes, three new carbon-carbon bonds and two to three stereogenic centers, including an all-carbon quaternary stereocenter could be created in acyclic systems. Because 1,3-diaxial interactions are now produced with the axial substituent, an increase in the substituent size on the zinc atom decreases the diastereoselectivity. © 2013 American Chemical Society.


Standera M.,ETH Zurich | Hafliger R.,ETH Zurich | Gershoni-Poranne R.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Stanger A.,Lise Meitner Minerva Center for Computational Quantum Chemistry | And 4 more authors.
Chemistry - A European Journal | Year: 2011

A chain of circumstantial evidence for the existence of the first fully conjugated, double-stranded cycles is presented. The products have the structure of the belt-region of fullerene C84 (D2) and carry either four hexyl chains or four phenyl groups. The unsubstituted parent cycle is also presented. The chain of evidence is mainly based on mass spectrometric analysis and trapping reactions, the latter being supported by quantum mechanical calculations. It is also of importance that the phenyl-substituted and unsubstituted products cannot undergo a [1,5] hydrogen shift, the only reasonable side-reaction that recently could not be excluded for the alkyl-substituted analogue. It is concluded that the fully aromatic targets truly exist in the gas phase. Whether they can be generated in solution under the applied conditions cannot yet be firmly decided; theoretical evidence speaks against. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Berkovich I.,Ben - Gurion University of the Negev | Mavila S.,Ben - Gurion University of the Negev | Iliashevsky O.,Ben - Gurion University of the Negev | Kozuch S.,Ben - Gurion University of the Negev | And 2 more authors.
Chemical Science | Year: 2016

High molecular weight polybutadienes and rhodium complexes were used to produce single chain organometallic nanoparticles. Irradiation of high cis-polybutadiene in the presence of a photosensitizer isomerised the double bonds to produce differing cis/trans ratios within the polymer. Notably, a higher cis percentage of carbon-carbon double bonds within the polymer structure led to faster binding of metal ions, as well as their faster removal by competing phosphine ligands. The experimental results were supported and rationalized by DFT computations. © The Royal Society of Chemistry 2016.


Levin A.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Basheer A.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Marek I.,Lise Meitner Minerva Center for Computational Quantum Chemistry
Synlett | Year: 2010

The stereodivergent carbometalation of substituted ynol ethers is reported and both isomers could be obtained at will depending of the nature of the OR group. © Georg Thieme Verlag Stuttgart New York.


Minko Y.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Pasco M.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Lercher L.,Lise Meitner Minerva Center for Computational Quantum Chemistry | Marek I.,Lise Meitner Minerva Center for Computational Quantum Chemistry
Nature Protocols | Year: 2013

This protocol describes a new approach for the preparation of stereodefined trisubstituted chiral enolate species, avoiding conventional asymmetric enolization of carbonyl compounds. This protocol was developed as a single-flask synthetic sequence and therefore does not require isolation or purification of intermediate compounds. The sequence starts from a regioselective carbocupration reaction of readily accessible chiral ynamides; this is followed by oxidation of the generated vinylcuprate with a commonly available oxidizing reagent (tert-butyl hydroperoxide) in order to generate an enolate that completely retains its configuration. This synthetic protocol has been applied to the preparation of aldol and Mannich-type adducts. The procedure reported here requires a simple reaction setup commonly available in all synthetic laboratories and takes ∼6 h for completion and 2 h for isolation and purification. Final products are valuable diastereomerically and enantiomerically enriched building blocks for organic synthesis containing all-carbon quaternary stereocenters in acyclic systems. © 2013 Nature America, Inc. All rights reserved.

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