Showing papers on "Axial chirality published in 2016"
TL;DR: In this article, the authors summarize the different strategies imagined by chemists to control axial chirality of biaryl structures, focusing on asymmetric catalytic processes with transition metals.
211 citations
TL;DR: Suitably substituted enantioenriched 4-aryl-1,4-dihydro-pyridines prepared by an organocatalytic enantioselective Michael addition were oxidized with MnO2 into axially chiral 4-arylpyridine with central-to-axial chirality conversion.
Abstract: Suitably substituted enantioenriched 4-aryl-1,4-dihydro-pyridines prepared by an organocatalytic enantioselective Michael addition were oxidized with MnO2 into axially chiral 4-arylpyridines with central-to-axial chirality conversion. Moderate to complete percentages (cp) were observed, and a model for the conversion of chirality is discussed.
130 citations
TL;DR: A highly enantioselective synthesis of trisubstituted allenes has been achieved through Cu(I)-catalyzed cross-coupling of aryldiazoalkanes and terminal alkynes with chiral bisoxazoline ligands.
Abstract: A highly enantioselective synthesis of trisubstituted allenes has been achieved through Cu(I)-catalyzed cross-coupling of aryldiazoalkanes and terminal alkynes with chiral bisoxazoline ligands Alkynyl migratory insertion of Cu(I) carbene is proposed as the key step for the construction of axial chirality
128 citations
TL;DR: A class of urazole with axial chirality by restricted rotation around an N–Ar bond is discovered by using bifunctional organocatalytic asymmetric tyrosine click-like reaction in high yields with excellent enantioselectivity under mild reaction conditions.
Abstract: Axially chiral compounds play an important role in areas such as asymmetric catalysis. The tyrosine click-like reaction is an efficient approach for synthesis of urazoles with potential applications in pharmaceutical and asymmetric catalysis. Here we discover a class of urazole with axial chirality by restricted rotation around an N-Ar bond. By using bifunctional organocatalyst, we successfully develop an organocatalytic asymmetric tyrosine click-like reaction in high yields with excellent enantioselectivity under mild reaction conditions. The excellent remote enantiocontrol of the strategy originates from the efficient discrimination of the two reactive sites in the triazoledione and transferring the stereochemical information of the catalyst into the axial chirality of urazoles at the remote position far from the reactive site.
106 citations
TL;DR: This Focus Review summarizes asymmetric organocatalytic methods for the synthesis of axially, planar, and helical chiral compounds as useful chiral building blocks.
Abstract: Axially, planar, and helical chiral compounds are indispensable building blocks in modern organic synthesis. A wide variety of chiral ligands and catalysts were designed based on these chiral scaffolds, and these chiral ligands and catalysts were used for various catalytic asymmetric transformations to produce important chiral compounds in an optically enriched form. Furthermore, these chiral skeletons are found in the structure of biologically active natural products. Thus, the development of efficient enantioselective methods for the synthesis of these chiral compounds is an important task in the field of organic chemistry. In the last few years, organocatalyzed approaches, which are one of the most reliable catalytic asymmetric methods, became a hot topic. This Focus Review summarizes asymmetric organocatalytic methods for the synthesis of axially, planar, and helical chiral compounds as useful chiral building blocks.
89 citations
TL;DR: In the presence of (R)-SEGPHOS-PdCl2 catalyst, 5-endo-hydroaminocyclization of various 2-(tert-butyl)-N-(2-ethynylphenyl)anilines proceeds enantioselectively to afford optically active N-C axially chiral N-(2−C)indole derivatives in good yields.
35 citations
TL;DR: The present work clarifies the cyclostereoisomerism of a cyclophenanthrenylene nanohoop possessing both E/Z- and R/S-geometries at the biaryl linkages and reports structural information reported here, such as geometric descriptors and anomalous dynamics, may shed light on the common structures of various nanohoops.
Abstract: The stereochemistry of cycloarylene nanohoops gives rise to unique cyclostereoisomerism originating from hoop-shaped molecular shapes. However, cyclostereoisomerism has not been well understood despite the ever-increasing number of structural variants. The present work clarifies the cyclostereoisomerism of a cyclophenanthrenylene nanohoop possessing both E/Z- and R/S-geometries at the biaryl linkages. Involvement of the R/S axial chirality in the nanohoop leads to the deviation of the structure from a coplanar belt shape and allows for structural variations with 51 stereoisomers with E/Z- and R/S-geometries. Experimental investigations of the dynamic behaviors of the cyclophenanthrenylene nanohoop revealed the presence of two-stage isomerization processes taking place separately at the E/Z- and R/S-linkages. Consequently, despite the presence of E/Z-fluctuations, the R/S axial chirality resulted in a separable pair of enantiomers. The structural information reported here, such as geometric descriptors and...
32 citations
TL;DR: A highly torquoselective process for simultaneous control of central and axial chirality by the annulation of terminally substituted ynamides with o-quinone methides with 2-amino-4H-chromenes is reported.
30 citations
TL;DR: The first natural occurrence in optically active form of the dimeric flavonoid agathisflavone and definition of its axial chirality using chiroptical spectroscopic methods are described.
Abstract: The first natural occurrence in optically active form of the dimeric flavonoid agathisflavone and definition of its axial chirality using chiroptical spectroscopic methods are described. The experimental electronic circular dichroism, electronic dissymmetry factor, optical rotatory dispersion, vibrational circular dichroism (VCD), and vibrational dissymmetry factor spectra of agathisflavone are presented and analyzed with their corresponding quantum chemical predictions to definitively assign the axial chirality of (−)-agathisflavone as (aS).
28 citations
TL;DR: A cheap and modular synthesis of a novel family of chiral ferrocenyl diols in excellent yields with excellent enantio- and diastereoselectivity (>99 % ee and 99’% de).
Abstract: Readily available chiral diol scaffolds are useful as sources of chirality for asymmetric synthesis, however, few such scaffolds are readily available in enantiopure form. Reported herein is a cheap and modular synthesis of a novel family of chiral ferrocenyl diols in excellent yields with excellent enantio- and diastereoselectivity (>99 % ee and 99 % de). These diols possess not only planar and central chirality, but also axial chirality around the central iron atom. Characterization of these diols by X-ray crystallography revealed intra- and intermolecular hydrogen-bond networks depending on substitution at the carbinol positions. The potential of these diols as catalysts was subsequently demonstrated in an asymmetric hetero-Diels-Alder reaction which provided cycloadducts in up to 84 % yield with ee values ranging from -92 to +72 %.
27 citations
TL;DR: In this paper, the efficient desymmetrization of N -(2- tert -butylphenyl)maleimides was realized by means of a Michael addition reaction of a series of carbon nucleophiles generating the corresponding axially chiral succinimides in high yields.
TL;DR: Such chiral phosphine-internal olefin hybrid type ligands as N-1-adamantyl-N-cinnamylaniline derivatives 1 with C(aryl)-N(amine) bond axial chirality were synthesized and utilized for the palladium-catalyzed asymmetric allylic alkylation of indoles to afford the desired products in high enantioselectivities.
Abstract: Such chiral phosphine–internal olefin hybrid type ligands as N-1-adamantyl-N-cinnamylaniline derivatives 1 with C(aryl)–N(amine) bond axial chirality were synthesized and utilized for the palladium-catalyzed asymmetric allylic alkylation of indoles to afford the desired products in high enantioselectivities (up to 98% ee).
TL;DR: Two new dichlorinated diphenylmethanes containing both point and axial chirality, (±)-pestalachlorides E (1) and F (2), were isolated from a marine-derived Pestalotiopsis fungus and showed potent antifouling activities against the larval settlement of the barnacle Balanus amphitrite.
Abstract: Marine life forms are an important source of structurally diverse and biologically active natural products. As a unique case of both enantiomeric and atropisomeric isomers being present in one marine natural product structure, two new dichlorinated diphenylmethanes containing both point and axial chirality, (±)-pestalachlorides E (1) and F (2), were isolated from a marine-derived Pestalotiopsis (ZJ-2009-7-6) fungus. Both of them showed potent antifouling activities against the larval settlement of the barnacle Balanus amphitrite at nontoxic concentrations with EC50 values of 1.65 and 0.55 μg mL−1, respectively, and antifouling activity was detected for the first time for this class of metabolites.
TL;DR: In this article, the most recent achievements in dynamic metal-catalyzed cross couplings of racemic substrates are collected and discussed according to the nature of the deracemization step.
Abstract: The development of stereoselective metal-catalyzed cross-coupling reactions over the past 30 years has revolutionized the way in which C–C, C–N, and C–X bonds are formed in an enantiomerically pure form. In particular asymmetric reactions that transform racemic substrates into enantioenriched products in high, ideally quantitative, yields are particularly appealing. Consequently, many deracemization processes have been developed, implying conceptually diverse strategies such as dynamic kinetic asymmetric transformation (DYKAT), dynamic kinetic resolution (DKR), and stereoconvergence. In this review the most recent achievements in dynamic metal-catalyzed cross couplings of racemic substrates are collected and discussed according to the nature of the deracemization step. 1 Introduction 2 Deracemization by Dynamic Kinetic Resolution (DKR)/Dynamic Kinetic Asymmetric Transformation (DYKAT) 2.1 DKR towards the Control of Central Chirality 2.2 DYKAT towards the Control of Central Chirality 2.3 DKR/DYKAT towards the Control of Axial Chirality 3 Deracemization Involving a Stereoconvergent Transformation 4 Conclusion
TL;DR: This material is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form.
TL;DR: In this article, an efficient methodology for kinetic resolution of axially chiral 2-amino-1,1′-biaryl compounds as useful chiral building blocks was developed by means of binaphthyl-modified chiral quaternary ammonium salt-catalyzed Nallylations under phase-transfer conditions.
TL;DR: It was found that the chirality relay from axially chiral 1,1'-binaphthyl to propeller chiralities of the trivalent boron center can be realized when a Me2 N and a Mes2 B group (Mes=mesityl) are introduced at the 2,2'-positions of the 1, 1'-binAPHthyl skeleton (BN-BNaph).
Abstract: It is a challenging issue to achieve propeller chirality for triarylboranes owing to the low transition barrier between the P and M forms of the boron center. Herein, we report a new strategy to achieve propeller chirality of triarylboranes. It was found that the chirality relay from axially chiral 1,1'-binaphthyl to propeller chirality of the trivalent boron center can be realized when a Me2 N and a Mes2 B group (Mes=mesityl) are introduced at the 2,2'-positions of the 1,1'-binaphthyl skeleton (BN-BNaph) owing to the strong π-π interaction between the Me2 N-bonded naphthyl ring and the phenyl ring of one adjacent Mes group, which not only exerts great steric hindrance on the rotation of the two Mes groups but also gives unequal stability to the two configurations of the boron center for a given configuration of the binaphthyl moiety. The stereostructures of the boron center were fully characterized through 1 H NMR spectroscopy, X-ray crystal analyses, and theoretical calculations. Detailed comparisons with the analog BN-Ph-BNaph, in which the Mes2 B group is separated from 1,1'-binaphthyl by a para-phenylene spacer, confirmed the essential role of π-π interaction for the successful chirality relay in BN-BNaph.
TL;DR: Circular dichroism (CD) spectroscopy was employed to show that the alcohol stereocenter of silylated, enantiopure secondary alcohols can transmit chirality to the aryl groups on the silicon resulting in a higher population of one helical conformation over another.
Abstract: Chirality transmission from point chirality to helical chirality was explored using triarylsilyl ethers. Circular dichroism (CD) spectroscopy was employed to show that the alcohol stereocenter of silylated, enantiopure secondary alcohols can transmit chirality to the aryl groups on the silicon resulting in a higher population of one helical conformation over another. Cotton effects characteristic of the aryl groups organized into one preferred conformation were observed for all of the compounds examined, which included both triphenyl- and trinaphthylsilyl groups. Alcohols with an R configuration typically induced a PMP helical twist, while an S configuration induced a MPM helical twist. Molecular modeling combined with solid-state structures also gave evidence signifying that point chirality adjacent to triphenylsilyl groups could bias the conformation of the phenyl groups. This work helps in our understanding of the origin of selectivity in our silylation-based kinetic resolutions and a role the phenyl g...
TL;DR: The structure-property relations indicate that intermolecular interactions cause a conformational change in the trimers possessing flexible odd-numbered methylene spacers to form helical conformers with axial chirality, which might induce chiral segregation and layer deformation to drive the chiral conglomerates.
Abstract: Chiral conglomerates of domains with opposite handedness have attracted much attention from researchers. We prepared a homologous series of achiral liquid crystal trimers in which two phenylpyrimidine units and one biphenyl unit were connected via flexible methylene spacers. We investigated their phase transition behaviour. Some trimers possessing odd-numbered spacers were found to exhibit a nematic phase and a dark chiral conglomerate phase possessing a layered structure. The chiral characteristics were confirmed by uncrossing the polarizers in opposite directions. The layer spacing detected using X-ray diffraction was about 80% of the molecular length. The structure–property relations indicate that intermolecular interactions cause a conformational change in the trimers possessing flexible odd-numbered methylene spacers to form helical conformers with axial chirality, which might induce chiral segregation and layer deformation to drive the chiral conglomerates.
TL;DR: The preparation of atropisomeric 2,1-borazaronaphthalenes is described and X-ray diffraction and Dynamic NMR data allowed structural and dynamic comparison with the analogue isosteric carbon compounds.
TL;DR: In this article, the authors describe the synthesis of axially chiral "Buchwald ligand"-like biphenylphosphines in highly enantioenriched form.
TL;DR: In this article, a terthienyl moiety was used as a fluorescent signaling unit, and their chiral recognition abilities were investigated on the basis of an enantioselective fluorescence response to aromatic nitro compounds as quenchers.
TL;DR: The conversion of propargylic carbonates into allenes via Pd-catalyzed coupling with arylboronic acids, followed by tandem intramolecular Alder-ene cyclization, proceeds with remote diastereocontrol in the formation of indenes possessing two stereogenic elements (stereocenter and chiral axis).
Abstract: The conversion of propargylic carbonates into allenes via Pd-catalyzed coupling with arylboronic acids, followed by tandem intramolecular Alder-ene cyclization, proceeds with remote diastereocontrol in the formation of indenes possessing two stereogenic elements (stereocenter and chiral axis). Highly configurationally stable atropisomers have been obtained with dr values up to >98:2. The reaction tolerates a range of commercially available functionalized arylboronic acids and allows the creation of C(sp2)–C(sp2) and C(sp2)–C(sp3) bonds in a single operation. Control experiments suggest that synergetic thermal and Pd-catalyzed cyclizations are likely to be involved in the second elementary step.
TL;DR: Compound 2 is the first report on the sterochemical assignment of a guaiane sesquiterpene by using the allylic axial chirality rule for the conjugated diene chromophore in combination with the calculated ECD spectrum.
TL;DR: In this article, the authors summarized recent progress made in their group on copper- or palladium-catalyzed asymmetric aryl carbon-nitrogen/oxygen coupling reactions using asymmetric desymmetrization or kinetic resolution strategies.
Abstract: Transition metal catalyzed coupling reactions of aryl halides with nucleophiles are valuable methods for the formation of aryl carbon–carbon or aryl carbon–heteroatom bonds. However, little attention has been focused on the asymmetric versions of such couplings. Besides direct coupling for the formation of axial chirality, asymmetric desymmetrization and kinetic resolution are two important strategies for achieving enantioselectivity in transition metal catalyzed aryl carbon–heteroatom couplings. This account summarizes recent progress made in our group on copper- or palladium-catalyzed asymmetric aryl carbon–nitrogen/oxygen coupling reactions using asymmetric desymmetrization or kinetic resolution strategies. 1 Introduction 2 Copper-Catalyzed Asymmetric N-Arylation 2.1 N-Arylation via Asymmetric Desymmetrization 2.1.1 First Type of Desymmetric N-Arylation 2.1.2 Second Type of Desymmetric N-Arylation 2.1.3 Double N-Arylation for Spirobilactams 2.2 N-Arylation via Kinetic Resolution 3 Asymmetric O-Arylation 3.1 Palladium/Spirocyclic Diphosphine Ligand System for O-Arylation via Asymmetric Desymmetrization 3.2 Palladium/Spirocyclic Diphosphine Monoxide Ligand System for O-Arylation via Asymmetric Desymmetrization 3.3 Copper/Diamine System for O-Arylation via Asymmetric Desymmetrization 4 Summary and Outlook
TL;DR: In this article, a 1,3-butadiyne-1,4-diamide (3) was synthesized and characterized by single crystal X-ray diffraction, 1H and 13C NMR, UV-fluorescence spectroscopy, cyclic voltammetry, TGA and DSC techniques.
TL;DR: A catalytic hydrogenation of cannabidiol derivatives known as phenylcyclohexenes was used to prepare epimeric (1R,1S) and/or rotameric (M,P) phenyl cyclohexanes, and the reaction is diastereoselective, in favor of the 1S epimer, when large groups are attached to the phenyl ring.
Abstract: A catalytic hydrogenation of cannabidiol derivatives known as phenylcyclohexenes was used to prepare epimeric (1R,1S) and/or rotameric (M,P) phenylcyclohexanes. The reaction is diastereoselective, in favor of the 1S epimer, when large groups are attached to the phenyl ring. For each epimer, variable-temperature NMR experiments, including EXSY spectroscopy and DFT calculations, were used to determine the activation energies of the conformational exchange arising from the restricted rotation about the aryl–C(sp3) bond that led to two unequally populated rotamers. The conformational preference arises essentially from steric interactions between substituents vicinal to the pivot bond. The conformers of epimers (1S)-2e,f show high rotational barriers of up to 92 kJ mol–1, unlike those of (1R)-2e,f and with much lower barriers of ∼72 kJ mol–1. The height of the barriers not only depends on the substituents at the axis of chirality but also is influenced by the position of a methyl group on the monoterpene ring....
TL;DR: An efficient catalyst-free microwave-assisted synthesis of tetrasubstituted pyrroles using dialkyl acetylenedicarboxylates and substituted monophenacylanilines has been developed.
TL;DR: In this work, chiral binaphthyl segment is directly fused into the central chromophore of a subphthalocyanine skeleton, resulting in a novel type of chiral subphthalOCyanine analogue (R/S)-1 of integrated inherent and induced chirality.
Abstract: Conventional conjugated systems are characteristic of only either inherent or induced chirality because of synthetic challenge in combination of chiral segment into the main chromophore. In this work, chiral binaphthyl segment is directly fused into the central chromophore of a subphthalocyanine skeleton, resulting in a novel type of chiral subphthalocyanine analogue (R/S)-1 of integrated inherent and induced chirality. Impressively, an obviously enhanced optical activity is discerned for (R/S)-1 molecules, and corresponding enhancement mechanism is elucidated in detail. The synthesis strategy based on rational molecular design will open the door towards fabrication of chiral materials with giant optical activity, which will have great potential in chiroptical devices.