Chiral Research Articles

Pd-Catalyzed Enantioselective Syntheses of Trisubstituted Allenes via Coupling of Propargylic Benzoates with Organoboronic Acids.

Enabled by the newly developed ligand, Ming-Phos, the first example of palladium-catalyzed highly enantioselective coupling of racemic propargylic benzoates with organoboronic acids for chiral allenes synthesis has been developed. Excellent asymmetric induction has been achieved with a decent substrate scope. Synthetic potentials for the construction of polycyclic compounds with multiple chiral centers have been demonstrated.

Qualitative, Quantitative Analysis and Chiral Characterization of the Essential Oils of Juniperus phoenicea L. and Juniperus oxycedrus L.

Isolation of oils from leaves of Juniperus phoenicea and Juniperus oxycedrus was obtained by steam distillation extraction method. The compositions of essential oils (EOs) were studied by means of GC-MS and GC-FID, using the internal standard method and relative response factors. Around ninety eight compounds were determined in total, representing 98.25 g/100 g of EO of J. phoenicea and 98.48 g/100 g of EO of J. oxycedrus, respectively. The volatile leaf oils were dominated by the terpenic hydrocarbon fractions (79.87 g/100 g) and (61.27 g/100 g) characterized by high contents of α-pinene (64.6 g/100 g) and (54.0 g/100 g) in J. phoenicea and J. oxycedrus, respectively, as the main component. Also, the enantiomeric distribution of α-pinene, sabinene, camphene, δ-3-carene, β-pinene, limonene, linalool, terpinen-4-ol, bornyl acetate, and borneol in both oils is presented for the first time.

A study of nucleon-nucleon scattering in covariant chiral effective field theory at the two-loop level

A study of nucleon-nucleon scattering in covariant chiral effective field theory at the two-loop level

Deracemization Enabled by Visible-Light Photocatalysis.

Deracemization is an ideal but challenging strategy for the conversion of a racemic mixture into a single enantiomer. Recent studies have demonstrated that visible-light photocatalysis could be utilized to promote selective deracemization of axially chiral allenes as well as cyclopropylquinolones and cyclic ureas with central chirality either through energy transfer or through a sequence of electron, proton, and hydrogen-atom transfer.

Prediction and assessment of nonlocal natural frequencies of DWCNTs: Vibration analysis

This paper aims to study vibration characteristics of chiral and zigzag double-walled carbon nanotubes entrenched on Donnell shell model. The Eringen\'s nonlocal elastic equations are being combined with Donnell shell theory to observe small scale response. Wave propagation is proposed technique to establish field equations of model subjected to four distinct end supports. A nonlocal model has been formulated to explore the frequency spectrum of both chiral and zigzag double-walled CNTs along with diversity of indices and nonlocal parameter. The significance of scale effect in relevance of length-to-diameter and thickness- to- radius ratios are discussed and displayed in detail. The numerical solution based on this nonlocal Donnell shell model can be further used to predict other frequency phenomena of double-walled and multi-walled CNTs.

Synthesis, Characterization, and Application of Segphos Derivative Having Diferrocenylphosphino-Donor Moieties

An axially chiral bisphosphine, Fc-Segphos (1), which possesses diferrocenylphosphino-donor moieties, was prepared as a racemate, and its optical resolution was achieved by the use of chiral HPLC. Ligand 1 coordinated to a palladium(II) cation in a bidentate fashion to construct a unique chiral environment at the palladium center due to the sterically demanding ferrocenyl groups. Ligand (R)-1 was applied in the palladium-catalyzed asymmetric synthesis of axially chiral allenes showing good enantioselectivity of up to 92% ee. In general, (R)-1 displayed better enantioselectivity than the parent Segphos in the palladium-catalyzed reaction, and the Pd/(R)-1 species showed up to 18% ee enhancement over the (R)-Segphos-derived palladium catalyst.

Synthesis of Allenes by 1,2-Elimination

Allenes represent an extremely important class of organic molecules, which, as a result of their twisted orthogonal π-systems can possess axial chirality. A wide array of methods for allene synthesis have been reported, such as the substitution of propargylic electrophiles, isomerization of alkynes and sigmatropic rearrangement. An alternative approach for the synthesis of allenes is 1,2-elimination of an appropriately substituted precursor. This mini-review highlights recent examples of 1,2-elimination processes, which target allenes including both polar and radical processes. The main focus is upon how control over the stereospecificity (e.g. syn- or anti-) of the 1,2-elimination process can enable the synthesis of enantioenriched axially chiral allenes. Recent developments in this field are presented including both enantiospecific and catalytic asymmetric methods.

Study on the covariant chiral effective field theory of vector meson

Study on the covariant chiral effective field theory of vector meson

Influence of vacancy defects on vibration analysis of graphene sheets applying isogeometric method: Molecular and continuum approaches

The main objective of this research paper is to consider vibration analysis of vacancy defected graphene sheet as a nonisotropic structure via molecular dynamic and continuum approaches. The influence of structural defects on the vibration of graphene sheets is considered by applying the mechanical properties of defected graphene sheets. Molecular dynamic simulations have been performed to estimate the mechanical properties of graphene as a nonisotropic structure with single- and double- vacancy defects using open source well-known software i.e., large-scale atomic/molecular massively parallel simulator (LAMMPS). The interactions between the carbon atoms are modelled using Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential. An isogeometric analysis (IGA) based upon non-uniform rational B-spline (NURBS) is employed for approximation of single-layered graphene sheets deflection field and the governing equations are derived using nonlocal elasticity theory. The dependence of small-scale effects, chirality and different defect types on vibrational characteristic of graphene sheets is investigated in this comprehensive research work. In addition, numerical results are validated and compared with those achieved using other analysis, where an excellent agreement is found. The interesting results indicate that increasing the number of missing atoms can lead to decrease the natural frequencies of graphene sheets. It is seen that the degree of the detrimental effects differ with defect type. The Young\'s and shear modulus of the graphene with SV defects are much smaller than graphene with DV defects. It is also observed that Single Vacancy (SV) clusters cause more reduction in the natural frequencies of SLGS than Double Vacancy (DV) clusters. The effectiveness and the accuracy of the present IGA approach have been demonstrated and it is shown that the IGA is efficient, robust and accurate in terms of nanoplate problems.

Theoretical survey of the photochemical deracemization mechanism of chiral allene 3-(3,3-dimethyl-1-buten-1-ylidene)-2-piperidinone

The photochemical deracemization mechanism of the chiral allene 3-(3,3-dimethyl-1-buten-1-ylidene)-2-piperidinone in the presence of photosensitizer thioxanthone is theoretically investigated by using a density functional theory (DFT) method.

Regio- and diastereoselective reactions of chiral secondary alkylcopper reagents with propargylic phosphates: preparation of chiral allenes.

The diastereoselective SN2′-substitution of secondary alkylcopper reagents with propargylic phosphates enables the preparation of stereodefined alkylallenes. By using enantiomerically enriched alkylcopper reagents and enantioenriched propargylic phosphates as electrophiles anti-SN2′-substitutions were performend leading to α-chiral allenes in good yields with excellent regioselectivity and retention of configuration. DFT-calculations were performed to rationalize the structure of these alkylcopper reagents in various solvents, emphasizing their configurational stability in THF.

Influence of chirality on two-dimensionaldeformations of twisted flexoelectric nematic layers

Dwuwymiarowe deformacje indukowane polem elektrycznym w warstwach cieklych krysztalow nematycznych posiadających wlaściwości fleksoelektryczne byly symulowane numerycznie. Zbadano wplyw chiralnych domieszek na strukture tych odksztalcen i ich rozwoj pod wplywem pola elektrycznego. Stwierdzono, ze chiralnośc wplywa glownie na kierunek odksztalcen, podczas gdy napiecie progowe na odksztalcenie i przestrzenny okres odksztalcen slabo zalezą od chiralności nematyka. Stwierdzono, ze chiralnośc wplywa glownie na kierunek odksztalcen, podczas gdy jej wplyw na napiecie progowe i na przestrzenny okres odksztalcen jest nieznaczny.

Enantioselective Synthesis of Multisubstituted Allenes by Cooperative Cu/Pd‐Catalyzed 1,4‐Arylboration of 1,3‐Enynes

AbstractA cooperative Cu/Pd‐catalyzed enantioselective synthesis of multisubstituted allenes is established. By employing chiral sulfoxide phosphine (SOP)/Cu and PdCl2(dppf) complexes as catalysts, the 1,4‐arylboration of 1,3‐enynes provides an efficient approach to trisubstituted chiral allenes with up to 92 % yield and 97:3 er. Furthermore, by using 2‐substituted 1,3‐enynes as substrates, the tetrasubstituted chiral allenes were successfully generated using this strategy. Finally, theoretical calculations indicate that the transmetallation of the allenylcopper species is the rate‐limiting step of this transformation.

Enantioselective Synthesis of Multisubstituted Allenes by Cooperative Cu/Pd-Catalyzed 1,4-Arylboration of 1,3-Enynes.

A cooperative Cu/Pd-catalyzed enantioselective synthesis of multisubstituted allenes is established. By employing chiral sulfoxide phosphine (SOP)/Cu and PdCl2 (dppf) complexes as catalysts, the 1,4-arylboration of 1,3-enynes provides an efficient approach to trisubstituted chiral allenes with up to 92 % yield and 97:3 er. Furthermore, by using 2-substituted 1,3-enynes as substrates, the tetrasubstituted chiral allenes were successfully generated using this strategy. Finally, theoretical calculations indicate that the transmetallation of the allenylcopper species is the rate-limiting step of this transformation.

Pd-Catalyzed Enantioselective Heck Reaction of Aryl Triflates and Alkynes.

The first palladium-catalyzed asymmetric Heck reaction between aryl triflates and alkynes to give trisubstituted allenes with high er under mild reaction conditions is described. The key to the success is the discovery and fine-tuning of the different N-substituents of Xu-Phos, which ensure the enantioselectivity and reactivity. Synthetic transformation of the chiral allenes with high chirality transfer was also demonstrated.

Chirality; Father

Chirality; Father

Synthesis of Chiral 3-Substituted Benzoquinone Compounds Through Asymmetric Catalytic Tandem Reaction with Chiral Phosphoramide as Catalyst

Synthesis of Chiral 3-Substituted Benzoquinone Compounds Through Asymmetric Catalytic Tandem Reaction with Chiral Phosphoramide as Catalyst

Chemo-, Regio-, Diastereo-, and Enantioselective Palladium Allylic Alkylation of 1,3-Dioxaboroles as Synthetic Equivalents of α-Hydroxyketones

We describe the development of a Pd-catalyzed asymmetric allylic alkylation (Pd-AAA) of acyclic α-hydroxyketones using boronic acids as traceless templates. Condensation of boronic acids with hydroxyketones generates 1,3-dioxaboroles, which can be used directly as pronucleophiles in Pd-AAA reactions. This strategy enables control of the enolate geometry, while removing the issue of O-alkylation. Allylic alcohols can be directly ionized in the presence of Pd(0) and chiral ligands to afford alkylation products with regio- and enantioselectivity. Additionally, a dynamic kinetic asymmetric transformation of allenyl electrophiles affords C-alkylation products in high regio-, diastereo-, and enantioselectivity. To the best of our knowledge, this method represents the first example in Pd-AAA for setting point chirality on a nucleophile simultaneous to stereoinduction on an axial chiral allene.

Cu-Catalyzed SN2' Substitution of Propargylic Phosphates with Vinylarene-Derived Chiral Nucleophiles: Synthesis of Chiral Allenes.

A new Cu-catalyzed enantioselective three-component (i.e., styrenes, B2pin2, and propargylic phosphates) allenylation via an SN2' substitution of propargylic electrophiles with vinylarene-derived chiral nucleophiles is presented. This method provides an efficient and enantioselective approach to access a range of optically pure di-(1,1-), tri-, and tetra-substituted allenes with α-central chirality and axial chirality in excellent chemo-, regio-, diastereo-, and enantioselectivities.

Preparation of Chiral Allenes through Pd-Catalyzed Intermolecular Hydroamination of Conjugated Enynes: Enantioselective Synthesis Enabled by Catalyst Design.

In this study, we establish that conjugated enynes undergo selective 1,4-hydroamination under Pd catalysis to deliver chiral allenes with pendant allylic amines. Several primary and secondary aliphatic and aryl-substituted amines couple with a wide range of mono- and disubstituted enynes in a nonenantioselective reaction where DPEphos serves as the ligand for Pd. Benzophenone imine acts as an ammonia surrogate to afford primary amines in a two-step/one-pot process. Examination of chiral catalysts revealed a high degree of reversibility in the C-N bond formation that negatively impacted enantioselectivity. Consequently, an electron-poor ferrocenyl-PHOX ligand was developed to enable efficient and enantioselective enyne hydroamination.