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Inherently chiral calix[4]arenes via oxazoline directed ortholithiation: synthesis and probe of chiral space.

ABSTRACT: The diastereoselective oxazoline-directed lithiation of calix[4]arenes is reported with diastereoselective ratios of greater than 100:1 in some instances. Notably, it has been found that the opposite diastereomer can be accessed via this approach merely through the choice of an alkyllithium reagent. The inherently chiral oxazoline calix[4]arenes have also been preliminarily examined as ligands in the palladium-catalyzed Tsuji-Trost allylation reaction, returning results comparable to their planar chiral ferrocene counterparts pointing towards future application of these types of compounds.

SUBMITTER: Herbert SA

PROVIDER: S-EPMC4273304 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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Inherently chiral calix[4]arenes via oxazoline directed ortholithiation: synthesis and probe of chiral space.

Herbert Simon A SA van Laeren Laura J LJ Castell Dominic C DC Arnott Gareth E GE

Beilstein journal of organic chemistry 20141125

The diastereoselective oxazoline-directed lithiation of calix[4]arenes is reported with diastereoselective ratios of greater than 100:1 in some instances. Notably, it has been found that the opposite diastereomer can be accessed via this approach merely through the choice of an alkyllithium reagent. The inherently chiral oxazoline calix[4]arenes have also been preliminarily examined as ligands in the palladium-catalyzed Tsuji-Trost allylation reaction, returning results comparable to their plana ...[more]

PMID: 25550740

Similar Datasets

Correction: Inherently chiral calix[4]arenes via oxazoline directed ortholithiation: synthesis and probe of chiral space.

Project description:[This corrects the article DOI: 10.3762/bjoc.10.291.].

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Synthesis of deep-cavity fluorous calix[4]arenes as molecular recognition scaffolds.

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Synthesis of Ionizable Calix[4]arenes for Chelation of Selected Divalent Cations.

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Heterometallic cobalt(ii) calix[6 and 8]arenes: synthesis, structure and electrochemical activity.

Project description:Heterometallic cobalt p-tert-butylcalix[6 and 8]arenes have been generated from the in situ reaction of lithium reagents (n-BuLi or t-BuOLi) or NaH with the parent calix[n]arene and subsequent reaction with CoBr2. The reverse route, involving the addition of in situ generated Li[Co(Ot-Bu)3] to p-tert-butylcalix[6 and 8]arene, has also been investigated. X-ray crystallography reveals the formation of complicated products incorporating differing numbers of cobalt and lithium or sodium centers, often with positional disorder, as well as, in some cases, the retention of halide. The electrochemical analysis revealed several oxidation events related to the subsequent oxidation of Co(ii) centers and the reduction of the metal cation at negative potentials. Moreover, the electrochemical activity of the phenol moieties of the parent calix[n]arenes resulted in dimerized products or quinone derivatives, leading to insoluble oligomeric products that deposit and passivate the electrode. Preliminary screening for electrochemical proton reduction revealed good activity for a number of these systems. Results suggest that [Co6Na(NCMe)6(μ-O)(p-tert-butylcalix[6]areneH)2Br]·7MeCN (6·7MeCN) is a promising molecular catalyst for electrochemical proton reduction, with a mass transport coefficient, catalytic charge transfer resistance and current magnitude at the catalytic turnover region that are comparable to those of the reference electrocatalyst (Co(ii)Cl2).

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Synthesis of Chiral Allylic Esters by Using the New Recyclable Chiral Heterogeneous Oxazoline-Based Catalysts.

Project description:A new class of recyclable supported chiral heterogeneous ligands has been synthesized by the reaction of functionalized mesoporous SBA-15 with aliphatic- and aromatic-substituted chiral amino oxazoline ligands. The obtained chiral heterogeneous ligands were characterized by several techniques such as Fourier transform infrared, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and BET-BJH. The application of these new heterogeneous ligands in copper-catalyzed asymmetric allylic oxidation of olefins by using perester showed better yields up to 95% and better enantioselectivities up to 96% compared to the corresponding homogeneous catalysts. These findings can be considered as an important step in the advancement of green chemistry. Investigation of the recyclability of the catalysts confirmed that they were easily recovered and reused eight times without significant losses in reactivity, yield, and enantioselectivity.

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Anion responsive TTF-appended calix[4]arenes. Synthesis and study of two different conformers.

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Interrogating the Crucial Interactions at Play in the Chiral Cation-Directed Enantioselective Borylation of Arenes.

Project description:Rendering a common ligand scaffold anionic and then pairing it with a chiral cation represents an alternative strategy for developing enantioselective versions of challenging transformations, as has been recently demonstrated in the enantioselective borylation of arenes using a quinine-derived chiral cation. A significant barrier to the further generalization of this approach is the lack of understanding of the specific interactions involved between the cation, ligand, and substrate, given the complexity of the system. We have embarked on a detailed computational study probing the mechanism, the key noncovalent interactions involved, and potential origin of selectivity for the desymmetrizing borylation of two distinct classes of substrate. We describe a deconstructive, stepwise approach to tackling this complex challenge, which involves building up a detailed understanding of the pairwise components of the nominally three component system before combining together into the full 263-atom reactive complex. This approach has revealed substantial differences in the noncovalent interactions occurring at the stereodetermining transition state for C-H oxidative addition to iridium for the two substrate classes. Each substrate engages in a unique mixture of diverse interactions, a testament to the rich and privileged structure of the cinchona alkaloid-derived chiral cations. Throughout the study, experimental support is provided, and this culminates in the discovery that prochiral phosphine oxide substrates, lacking hydrogen bond donor functionality, can also give very encouraging levels of enantioselectivity, potentially through direct interactions with the chiral cation. We envisage that the findings in this study will spur further developments in using chiral cations as controllers in asymmetric transition-metal catalysis.

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Synthesis of upper rim-double-bridged calix[4]arenes bearing seven membered rings and related compounds.

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Synthesis of Ultrastable and Bioconjugable Ag, Au, and Bimetallic Ag_Au Nanoparticles Coated with Calix[4]arenes.

Project description:Compared to gold nanoparticles, silver nanoparticles are largely underexploited for the development of plasmonic nanosensors. This is mainly due to their easy chemical degradation through oxidation, poor colloidal stability, and usually broad size distribution after synthesis, which leads to broad localized surface plasmon resonance bands. Coatings based on polymers such as poly(ethylene glycol) (PEG) or poly(vinylpyrrolidone) (PVP) and plant extracts have been used for the stabilization of AgNPs; however, these thick coatings are not suitable for sensing applications as they isolate the metallic core. The examples of stable AgNPs coated with a thin organic layer remain scarce in comparison to their gold counterparts. In this work, we present a convenient one-step synthesis strategy that allows to obtain unique gold, silver, and bimetallic NPs that combine all of the properties required for biosensing applications. The NPs are stabilized by a tunable calix[4]arene-based monolayer obtained through the reduction of calix[4]arene-tetradiazonium salts. These multidentate ligands are of particular interest as (i) they provide excellent colloidal and chemical stabilities to the particles thanks to their anchoring to the surface via multiple chemical bonds, (ii) they allow the subsequent (bio)conjugation of (bio)molecules under mild conditions, and (iii) they allow a control over the composition of mixed coating layers. Ag and Ag_Au nanoparticles of a high stability are obtained, opening perspectives for development of numerous biosensing applications.

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Adenine oligomer directed synthesis of chiral gold nanoparticles.

Project description:Precise control of morphology and optical response of 3-dimensional chiral nanoparticles remain as a significant challenge. This work demonstrates chiral gold nanoparticle synthesis using single-stranded oligonucleotide as a chiral shape modifier. The homo-oligonucleotide composed of Adenine nucleobase specifically show a distinct chirality development with a dissymmetric factor up to g ~ 0.04 at visible wavelength, whereas other nucleobases show no development of chirality. The synthesized nanoparticle shows a counter-clockwise rotation of generated chiral arms with approximately 200 nm edge length. The molecular dynamics and density functional theory simulations reveal that Adenine shows the highest enantioselective interaction with Au(321)R/S facet in terms of binding orientation and affinity. This is attributed to the formation of sequence-specific intra-strand hydrogen bonding between nucleobases. We also found that different sequence programming of Adenine-and Cytosine-based oligomers result in chiral gold nanoparticles' morphological and optical change. These results extend our understanding of the biomolecule-directed synthesis of chiral gold nanoparticles to sequence programmable deoxyribonucleic acid and provides a foundation for programmable synthesis of chiral gold nanoparticles.

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