Search

Choosing the optimal catalyst for a new transformation is challenging because the ideal molecular requirements of the catalyst for one reaction do not always simply translate to another. Large groups at the 3,3′ positions of the binaphthol rings are important for efficient stereoinduction but if they are too large this can lead to unusual or poor results. By applying a quantitative steric assessment of the substituents at the 3,3′ positions of the binaphthol ring, we have systematically studied the effect of modulating this group on enantioselectivity for a wide range of reactions involving imines, and verified this analysis using ONIOM calculations. We have shown that in most reactions, the stereochemical outcome depends on both proximal and remote sterics. Summarising detailed calculations into a simple qualitative model identifies and explains the steric features required for high selectivity. This model is consistent with seventy seven papers reporting reactions (over 1000 transformations in total), and provides a straightforward decision tree for selecting the best catalyst. [ABSTRACT FROM AUTHOR]

The racemate of an inherently chiral “spider ‐ like” octathiophene monomer T83, in which chirality is generated by torsion in its backbone, was synthesized. In the cover image, the (S) ‐ T83 has woven a highly selective chiral web in which enantiomorphic insects (l ‐ and d ‐ DOPA, R ‐ and S ‐ FcA) are differently entrapped. More information can be found in the Full Paper by P. R. Mussini, T. Benincori, R. Martinazzo et al. on page 10839. [ABSTRACT FROM AUTHOR]

Gold(I)-catalysed intermolecular hydroalkoxylation of enantioenriched 1,3-disubstituted allenes was previously reported to occur with poor chirality transfer due to rapid allene racemisation. The first intermolecular hydroalkoxylation of allenes with efficient chirality transfer is reported here, exploiting conditions that suppress allene racemisation. A full substrate scope study reveals that excellent regio- and stereoselectivities are achieved when a σ-withdrawing substituent is present. [ABSTRACT FROM AUTHOR]

Dynamically controlling the supramolecular chirality is of great significance in development of functional chiral materials, which is thus essential for the specific function implementation. As an external energy input, light is remote and accurate for modulating chiral assemblies. In non‐polarized light control, some photochemically reactive units (e. g. azobenzene, ɑ‐cyanostilbene, spiropyran, anthracene) or photo‐induced directionally rotating molecular motors were designed to drive chiral transfer or amplification. Besides, photoexcitation induced assembly based physical approach was also explored recently to regulate supramolecular chirality beyond photochemical reactions. In addition, circularly polarized light was applied to induce asymmetric arrangement of organic molecules and asymmetric photochemical synthesis of inorganic metallic nanostructures, in which both wavelength and handedness of circularly polarized light have effects on the induced supramolecular chirality. Although light‐triggered chiral assemblies have been widely applied in photoelectric materials, biomedical fields, soft actuator, chiral catalysis and chiral sensing, there is a lack of systematic review on this topic. In this review, we summarized the recent studies and perspectives in the constructions and applications of light‐responsive chiral assembled systems, aiming to provide better knowledge for the development of multifunctional chiral nanomaterials. [ABSTRACT FROM AUTHOR]

A stereoselective hypervalent iodine-promoted oxidative rearrangement of 1,1-disubstituted alkenes has been developed. This practically simple protocol provides access to enantioenriched α-arylated ketones without the use of transition metals from readily accessible alkenes. [ABSTRACT FROM AUTHOR]

Easily accessible and tunable chiral triazoles have been introduced as a novel class of C−H bond-based H-donors for anion-binding organocatalysis. They have proven to be effective catalysts for the dearomatization reaction of different N-heteroarenes. Although this dearomatization approach represents a powerful strategy to build chiral heterocycles, to date only a few catalytic methods to this end exist. In this work, the organocatalyzed enantioselective Reissert-type dearomatization of isoquinoline derivatives employing a number of structurally diverse chiral triazoles as anion-binding catalysts was realized. The here presented method was employed to synthesize a number of chiral 1,2-dihydroisoquinoline substrates with an enantioselectivity up to 86:14 e.r. Moreover, a thorough study of the determining parameters affecting the activity of this type of anion- binding catalysts was carried out. [ABSTRACT FROM AUTHOR]

Organocopper reagents react with readily available chiral conjugated diene-ynes to give indene derivatives bearing two stereogenic centres. The investigation of this original reaction in optically pure series demonstrates that a double transfer of chirality is operating. A stereocontrolled cascade involving SN2' followed by carbocupration and conjugate addition reactions accounts for the total recovery of the initial chirality. The scope and limitations of the reaction were investigated. The high diastereofacial discrimination in the cyclisation step allowed the construction of the quaternary stereocentre with excellent dr and ee, with the opposite configuration depending on the E- or Z-configuration of the alkene in the starting material. Post-functionalisation of indenes allowed the synthesis of indanyl derivatives containing four contiguous stereocentres. [ABSTRACT FROM AUTHOR]

Multicomponent metallo‐supramolecular assembly allows the rational combination of different building blocks. Discrete multifunctional hosts with an accessible cavity can be prepared in a non‐statistical fashion. We employ our shape‐complementary assembly (SCA) method to achieve for the first time integrative self‐sorting of heteroleptic PdII cages showing guest‐tunable circularly polarized luminescence (CPL). An enantiopure helicene‐based ligand (M or P configuration) is coupled with a non‐chiral emissive fluorenone‐based ligand (A or B) to form a series of Pd2L2L′2 assemblies. The modular strategy allows to impart the chiral information of the helicenes to the overall supramolecular system, resulting in CPL from the non‐chiral component. Guest binding results in a 4‐fold increase of CPL intensity. The principle offers potential to generate libraries of multifunctional materials with applications in molecular recognition, enantioselective photo‐redox catalysis and information processing. [ABSTRACT FROM AUTHOR]

The first chiral helicene‐NHC gold(I) complexes efficient in enantioselective catalysis were prepared. The L‐shaped chiral ligand is composed of an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold laterally substituted by a configurationally stable [5]‐helicenoid unit. The chiral information was introduced in a key post‐functionalization step of a NHC‐gold(I) complex bearing a symmetrical anionic fluoreno[5]helicene substituent, leading to a racemic mixture of complexes featuring three correlated elements of chirality, namely central, axial and helical chirality. After HPLC enantiomeric resolution, X‐ray crystallography and theoretical calculations enabled structural and stereochemical characterization of these configurationally stable NHC‐gold(I) complexes. The high potential in asymmetric catalysis is demonstrated in the benchmark cycloisomerization of N‐tethered 1,6‐enynes with up to 95 : 5 er. [ABSTRACT FROM AUTHOR]

"Chirality" governs many fundamental properties in chemistry and biochemistry. While early investigations on stereochemistry are primarily dedicated to static chirality, there is an increasing interest in the field of dynamic chirality (chiral switches). These chiral switches are essential in controlling the directionality in molecular motors. Dynamic chiralities are equally crucial in switchable stereoselectivity, switchable asymmetric catalysis and enantioselective separation. Herein, we limit our discussion to recent advances on stimuli‐induced chiroptical switching of axial, helical, and planar chirality in response to external stimuli. We also discuss a few examples of applications of the switchable chirality. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue is Yasuhiro Morisaki at Kwansei Gakuin University together with the group of Yoshiki Chujo at Kyoto University. The image depicts the circularly polarized luminescence of the dendrimer films described in their Full Paper. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

The synthesis of phosphorus molecules presenting a chiral center on the P‐atom, also known as P‐stereogenic compounds, has long attracted the curiosity of the scientific community. Indeed, these chemical compounds feature many peculiar properties, allowing their use in various fields of applications, ranging from medicine to enantioselective catalysis. However, their synthesis, and more particularly the introduction and retention of the chiral information on the phosphorus center, remains a very challenging task. That is why this review article focuses on the recent advances in the enantioselective synthesis of P‐stereogenic molecules, with a particular focus on the introduction of the chiral center on the phosphorus atom. This article summarizes the main synthetic approaches directed towards the enantioselective synthesis of such chemical entities with a historical perspective. Thus, approaches based on the use of chiral auxiliaries attached to the phosphorus atom and the use of chiral stoichiometric reagents will be discussed first, as they were historically the first to be developed. Then, the recent discoveries in the catalytic and enantioselective synthesis and the direct optical resolution of P‐chiral compounds will be discussed. [ABSTRACT FROM AUTHOR]

The pot‐economical, highly enantioselective synthesis of axially chiral biaryls was developed by using one‐pot organocatalyst‐mediated domino and aromatization reactions as key steps. The axial information of the precursor, which also has central chirality, was completely inverted in the final biaryls. The inversion of the axial information occurred in the conversion of the central chirality to the axial chirality of an oxidative aromatization step. [ABSTRACT FROM AUTHOR]

Sustainability concerns are the wind in the sails for the development of novel, more selective catalytic processes. Hence, chiral catalysts play a crucial role in the green production of enantioenriched compounds. To further increase the green profile of this approach, the use of solid‐supported catalytic species is appealing due to the reduced generation of waste, as well as the possibility of reusing the precious catalyst. Even more attractive is the implementation of flow processes based on these immobilized catalysts, a flexible strategy that allows to generate from milli‐ to multi‐gram amounts of chiral product with a reduced footprint set‐up. Herein, we will present the efforts devoted in our laboratory towards the immobilization of chiral catalysts and their use in single‐pass, highly enantioselective, flow processes. Proline, diarylprolinols, other aminocatalysts, squaramides, thioureas, phosphoric acids and even chiral ligands and metal‐based catalysts constitute our current toolkit of supported species for enantioselective catalysis. [ABSTRACT FROM AUTHOR]

An efficient kinetic resolution of axially chiral 2‐nitrovinyl biaryls was realized through organocatalytic asymmetric Michael addition of acetone to the nitroolefin moiety. Under the catalysis of a chiral thiophosphinamide derived from (1R,2R)‐1,2‐diphenylethane‐1,2‐diamine, racemic 2‐nitrovinyl biaryls were converted into highly enantiomer‐enriched 2‐nitrovinyl biaryls in 13–44% yields and a pair of separable Michael addition products bearing both axial and central chiralities in excellent stereocontrol. This represents the first successful application of asymmetric Michael addition of nitroolefins in kinetic resolution of axially chiral biaryls. [ABSTRACT FROM AUTHOR]

An enantioselective intermolecular addition reaction of azlactones, as carbon nucleophiles, with styrene derivatives, as simple olefins, was demonstrated using a newly developed chiral Brønsted acid catalyst, namely, F10BINOL‐derived N‐triflyl phosphoramide. Addition products having vicinal tetrasubstituted carbon centers, one of which is an all‐carbon quaternary stereogenic center, were formed in good yields with moderate to high stereoselectivities. Extremely high acidity of the new chiral Brønsted acid was confirmed by its calculated pKa value based on DFT studies and is the key to accomplishing not only high catalytic activity but also efficient stereocontrol in the intermolecular addition. [ABSTRACT FROM AUTHOR]

An enantioselective aryl transfer is promoted using chiral tricoordinated lithium amido aryl zincates that are easily accessible reagents and whose chiral appendage is simply recovered for reuse. The arylation reaction is run in good yields (60 % average on twenty substrates) and high enantiomeric excesses (95 % ee average). This occurs whatever the ortho, meta, or para substituent borne by the substrate and a complete chemoselectivity is observed with respect to the aldehyde function. Sensitive groups such as nitriles, esters, ketones, and enolisable substrates resist to the action of the ate reagent, warranting a large scope to this methodology. Chemo‐ and enantio‐selective nucleophilic aryl transfer: The key reactant is a chiral tricoordinated lithium amido aryl zincate of which the chiral appendage is simply recovered and reused. The arylation leaves intact sensitive functions such as esters, nitriles, ketones or enolisable sites, while running with aldehyde groups in good yields and high ee values, this whatever the ortho, meta, or para substituent borne by the substrate if aromatic. [ABSTRACT FROM AUTHOR]

The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing both axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted 3,3′‐bisindoles with 3‐indolylmethanols (up to 98 % yield, all >95:5 d.r. >99 % ee). This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles. This reaction not only provides a good example for simultaneously controlling axial and central chirality in one operation, but also serves as a new strategy for catalytic enantioselective construction of axially chiral 3,3′‐bisindole backbones from prochiral substrates. Bulk up: The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted 3,3′‐bisindoles with electrophiles. This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles. [ABSTRACT FROM AUTHOR]

A chiral CpxRhIII catalyst system in situ generated from a CpxRhI(cod) precatalyst and bis(o‐toluoyl) peroxide as activating oxidant was developed for a C−H activation/ring‐opening sequence between aryl ketoxime ethers and 2,3‐diazabicyclo[2.2.1]hept‐5‐enes. This transformation provides access to densely functionalized chiral cyclopentenylamines in excellent yields and enantioselectivities of up to 97:3 er. The reported method is also well suitable for asymmetric alkenyl C−H functionalizations of α,β‐unsaturated oxime ethers, furnishing skipped dienes with high levels of enantiocontrol. Hand in hand: A chiral CpxRhIII catalyst system generated from a CpxRhI(cod) precatalyst and bis(o‐toluoyl) peroxide engages in aryl and alkenyl C−H activation/ring‐opening sequences between ketoxime ethers and 2,3‐diazabicyclo[2.2.1]hept‐5‐enes. The transformation provides densely functionalized chiral cyclopentenylamines in excellent yields and high enantioselectivities. [ABSTRACT FROM AUTHOR]

The enantioselective synthesis of a series of C2‐symmetric 3,3′‐diarylated 1,1′‐spirobiindane‐7,7′‐diols (3,3′‐diaryl‐SPINOLs) was developed by sequential Rh‐catalyzed twofold asymmetric conjugate arylation/BF3‐promoted diastereoselective spirocyclization (>20:1 d.r. and >99 % ee for all examples). Some phosphoramidite ligands were prepared from the 3,3′‐Ph‐SPINOL and applied to several catalytic asymmetric reactions, and the 3,3′‐diarylated ligands showed higher enantioselectivities than the privileged nonsubstituted ligands. Going for a ′SPIN′: The enantioselective synthesis of a series of 3,3′‐diarylated 1,1′‐spirobiindane‐7,7′‐diols (3,3′‐diaryl‐SPINOLs) was developed using a sequential Rh‐catalyzed twofold asymmetric conjugate arylation/BF3‐promoted diastereoselective spirocyclization. Some phosphoramidite ligands were prepared from the 3,3′‐Ph‐SPINOL and applied to several catalytic asymmetric reactions, and the 3,3′‐diarylated ligands showed higher enantioselectivities than the privileged nonsubstituted ligands. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, a new capillary electrokinetic chromatography (EKC) approach using ethanediamine‐bonded poly (glycidyl methacrylate) (Ami‐PGMA) microspheres as pseudostationary phases (PSPs) for enantioseparation with a polysaccharide, chondroitin sulfate E (CSE), as the chiral selector. The CSE@Ami‐PGMA EKC system was applied to enantioseparate basic drugs, and distinct improved separations of tested enantiomers were obtained while comparing with the single CSE system (the resolution increased from 0.41 to 1.26 for nefopam, from 1.24 to 2.15 for laudanosine, and from 0.92 to 2.36 for amlodipine). The Ami‐PGMA microspheres were fully characterized by scanning electron microscopy (SEM) and Fourier Transform Infrared (FT‐IR) spectroscopy, and the results showed Ami‐PGMA microspheres were uniform and spherical in size (1 μm). Several principal parameters were systematically investigated, and the optimal chiral separations were obtained with Tris/H3PO4 (20 mM, pH 2.4, and 3.4 for NEF) containing 2.5% (w/v) CSE and 20‐μg Ami‐PGMA microspheres in 20°C. Subsequently, the concentrations of Ami‐PGMA microspheres and CSE were proved to be the dominant factors for the separation in the CSE@Ami‐PGMA EKC system by Statistical Product and Service Solutions (SPSS). The established EKC system using ethanediamine‐bonded poly (glycidyl methacrylate) microspheres as the PSP showed markedly improved enantioseparations compared with the single CSE system. [ABSTRACT FROM AUTHOR]

An unprecendented chiral sulfide catalyzed desymmetrizing enantioselective chlorination is disclosed. Various aryl‐tethered diolefins and diaryl‐tethered olefins afforded teralins and tricyclic hexahydrophenalene derivatives, respectively, bearing multiple stereogenic centers in high yields with excellent enantio‐ and diastereoselectivities. In contrast, the tertiary amine catalyst (DHQD)2PHAL led to a diastereomeric product. The products could be transformed into a variety of compounds, such as spiro‐N‐heterocycles. A chiral sulfide catalyzed the desymmetrizing enantioselective chlorination of various aryl‐tethered diolefins and diaryl‐tethered olefins to afford teralins and tricyclic hexahydrophenalene derivatives, respectively, bearing multiple stereogenic centers. In contrast, the tertiary amine catalyst (DHQD)2PHAL led to a diastereomeric product. The products could be transformed into diverse compounds such as spiro‐N‐heterocycles. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A highly enantioselective nucleophilic addition of phosphite esters to imines catalyzed by a chiral phase‐transfer catalyst has been developed. The process affords the hydrophosphonylation of imine products with quaternary stereocenters in good to high yields (up to 95 % yield) and excellent enantioselectivities (up to 99 % ee). A highly enantioselective nucleophilic addition of phosphite esters to versatile imines catalyzed by a cinchona alkaloid‐based chiral phase‐transfer catalyst has been developed. The process affords the desired hydrophosphonylation of imine products with quaternary stereocenters in good to high yields (up to 95 % yield) and excellent enantioselectivities (up to 99 % ee). And this straightforward protocol can be applied to gram scale reaction effectively. [ABSTRACT FROM AUTHOR]

Synthesis of the first enantiomerically pure chiral bambusurils is reported. The bambusurils were prepared on the gram scale without using any chromatography techniques. The bambusurils formed supramolecular complexes with all tested chiral carboxylates including amino acids and drug molecules with the enantioselectivity ranging from 1.1 to 3.2. Macrocyclization of glycoluril diastereomers leads to enantiomerically pure chiral bambusurils with the ability to recognize biologically relevant carboxylate anions. [ABSTRACT FROM AUTHOR]

Abstract: The regioselective and enantioselective synthesis of β‐indolyl cyclopentenamides, a versatile chiral building block, by asymmetric addition of indoles to α,β‐unsaturated iminium intermediates has been achieved through chiral anion catalysis. Key to the success of this methodology is the generation of a chiral anion‐paired ketone‐type α,β‐unsaturated iminium intermediate from α‐hydroxy enamides. Preliminary mechanistic studies and DFT calculations are consistent with a mechanism involving multiple, concurrent pathways for isomerization of the initially formed azaallylcation into the key α,β‐unsaturated iminium intermediate, all mediated by the phosphoric acid catalyst. [ABSTRACT FROM AUTHOR]

Abstract: A highly regio‐ and enantioselective hydrogenation of challenging tetrasubstituted allenyl sulfones has been developed, affording chiral allylic sulfones in good yields with excellent regio‐ and enantioselectivities (up to 99 % yield and 99 % ee). This method provides an efficient and concise route to chiral allylic sulfones, thus offering an atom‐economic process with a wide range of potential applications in organic synthesis and medicinal chemistry. [ABSTRACT FROM AUTHOR]

Abstract: A highly enantioselective synthesis of tetrahydroindolizines by catalytic multicomponent cycloaddition reactions of diazoacetate, pyridine, and alkenyloxindole was developed. Under the relay catalysis, involving an achiral iron(III) catalyst and chiral N,N′‐dioxide‐scandium(III) complex, a series of tetrahydroindolizines bearing different substituents were obtained in moderate to high yields (up to 99 %) with excellent diastereo‐ and enantioselectivities (up to >19:1 d.r., 99 % ee). [ABSTRACT FROM AUTHOR]

Abstract: The rhodium complex Λ‐Rh1 containing chiral pinene‐modified pyridine ligands is prepared through a two‐step synthetic procedure; it exhibits excellent reactivity and enantiocontrol towards the enantioselective Mukaiyama–Michael reaction of α,β‐unsaturated 2‐acyl imidazoles with silyl enol ethers, affording enantioenriched 1,5‐dicarbonyl compounds in good yields (up to 99 %) with excellent enantioselectivities (up to 99 % ee). [ABSTRACT FROM AUTHOR]

Optically active benzo[b]carbazole and benzo[b]acridine derivatives were prepared by Fischer indole or Friedländer quinoline annulation from 2‐oxodecalone‐4a‐carboxylates with a quaternary stereocenter. As an additional point for diversification, the target compounds carry a nitro function, which was transformed to an amide or lactam after reduction. The scaffold itself was accessed by asymmetric, copper catalyzed Michael reaction of a β‐oxoester with methyl vinyl ketone utilizing l‐valine diethyl amide as chiral auxiliary. Two enantiopure, epimeric compounds were obtained with 99 % ee and 92 % ee, which were separated and in parallel sequences submitted to intramolecular aldol reaction and catalytic hydrogenation furnishing the 2‐oxodecalone scaffolds. As a precursor for the primary amino group, the scaffolds contained a nitro function at their 6‐positions, which was reduced at the end of the synthetic sequence. The relative and absolute configurations of all three stereocenters were established by X‐ray crystallography. [ABSTRACT FROM AUTHOR]

Abstract: Ionic liquids, as a special class of organic compounds, have attracted ever‐growing interest in recent years. They have been employed in many organic transformations as a green alternative to volatile organic solvents and as a catalyst to modify catalytic activity and recyclability. Recent developments have demonstrated that ionic liquids might also have many benefits in asymmetric reactions. In this review, we survey the use of ionic liquids in asymmetric transformations, including the use of ionic liquids as reaction media in asymmetric reactions, ionic‐liquid‐tagged chiral catalysts for use in asymmetric synthesis, and supported ionic liquid catalysts in asymmetric transformations. [ABSTRACT FROM AUTHOR]

Abstract: A highly efficient strategy for the kinetic resolution of Michael adducts was realized using a chiral N‐heterocyclic carbene catalyst. The kinetic resolution provides a new convenient route to single diastereomers of cyclohexenes and Michael adducts in good yields with high enantiomeric excesses (up to 99 % ee with a selectivity factor of up to 458). This “two flies with one swat” concept allows the synthesis of these two synthetically valuable compound classes at the same time by a single transformation. [ABSTRACT FROM AUTHOR]

An organocatalytic approach for direct conversion of racemic diarylmethanols to valuable chiral diarylmethylamines is described. Different from the previously reported elegant “borrowing hydrogen” approach, the present process employs a distinct complementary formal SN1 strategy. This approach enjoys excellent enantioselectivity, mild conditions, broad scope, and easy product derivatization. Mechanistically, control experiments also provided important insights into some notable features, such as substrate kinetic resolution and reversibility as well as the critical role of the ortho‐ hydroxy group in the substrate. [ABSTRACT FROM AUTHOR]

Two enantiomerically pure chiral dioxidomolybdenum(VI) complexes (1 and 2) of the type [MoO2L] (L = dianionic, tetradentate ONNO‐ligand) were synthesized and investigated in enantioselective oxidation reactions. The solid‐state structures of complex 1 and 2, determined via single‐crystal X‐ray diffraction analysis revealed two fundamentally different coordination geometries: a C1‐symmetric cis‐β isomer (Λ‐1), and a C2‐symmetric cis‐α isomer (Δ‐2). In both cases, only one of the two possible helical enantiomers (Λ‐ or Δ‐helix) was formed. The complexes were examined as precatalysts in the epoxidation of the challenging prochiral substrate trans‐stilbene, using either tert‐butyl hydroperoxide (TBHP) or cumyl hydroperoxide (CHP) as oxidants. The asymmetric cis‐β complex 1 was found to be significantly more active in the epoxidation than its cis‐α counterpart 2, asymmetric induction was, however, negligible for both complexes. The complexes were also tested in catalytic enantioselective sulfoxidation reactions where chiral induction could be achieved, albeit small. The observed putative molybdenum oxido‐peroxido intermediate 1‐O2 could be identified as an important precomplex before formation of the active catalyst in sulfoxidation. [ABSTRACT FROM AUTHOR]

Abstract: Rapid development in the last decade has rendered chiral organoiodine(I/III) catalysis a reliable methodology in asymmetric catalysis. However, due to the severely limited numbers of effective organoiodine catalysts, many reactions still give low to modest enantioselectivity. We report herein a solution to this issue through the introduction of a pivotal indanol scaffold to the catalyst design. Our catalyst architecture exhibits the advantage of high modularity and thereby expedites catalyst optimization. The catalyst was optimized for the challenging and highly sought‐after hydrative dearomatization of 2‐substituted phenols at the 4‐position. [ABSTRACT FROM AUTHOR]

Abstract: Chiral metal–organic framework (CMOF) nanosheets only a few layers thick remain a virgin land waiting for exploration. Herein, the first examples of ultrathin CMOF nanosheets are prepared by the confinement growth of two‐dimensional (2D) chiral layers, which are assembled by helical metal–organic chains within microemulsion. This convenient and easily scaled up inverse microemulsion method gives a series of 2D CMOF nanosheets composed of variable metal nodes or chiral ligands. More significantly, thanks to the exceptionally large number of chiral sites exposed on surfaces, the as‐obtained CMOF nanosheets exhibit much higher enantioselectivity in chiral separation compared with their bulk counterparts. [ABSTRACT FROM AUTHOR]

Abstract: Medium‐sized lactams are important structural motifs found in a variety of bioactive compounds and natural products but are challenging to prepare, especially in optically active form. A Michael addition/proton transfer/lactamization organocascade process is described that delivers medium‐sized lactams, including azepanones, benzazepinones, azocanones, and benzazocinones, in high enantiopurity through the intermediacy of chiral α,β‐unsaturated acylammonium salts. An unexpected indoline synthesis was also uncovered, and the benzazocinone skeleton was transformed into other complex heterocyclic derivatives, including spiroglutarimides, isoquinolinones, and δ‐lactones. [ABSTRACT FROM AUTHOR]

Abstract: The enantioselective construction of axially chiral aryl‐naphthopyran skeletons was realized by organocatalytic atroposelective intramolecular [4+2] cycloaddition of in situ generated vinylidene ortho‐quinone methides, from 2‐ethynylphenol derivatives, with alkynes. Through this method, the heteroatropisomers were obtained with excellent yields and enantioselectivities. Moreover, a speculative model of the stereochemical outcome is proposed based on preliminary mechanistic studies. The products having various functional groups can be easily transformed into valuable intermediates as either potential ligands or organocatalysts. [ABSTRACT FROM AUTHOR]

A new method for the enantioselective synthesis of 5,5-disubstituted (quaternary) hydantoins was developed on the basis of an organocatalytic Michael reaction approach involving the use of 2-benzylthio-3,5-dihydroimidazol-4-ones as key hydantoin surrogates. The method is general with respect to the substitution pattern at the hydantoin N1 (alkyl, aryl, acyl), N3 (aryl), and C5 (linear/branched alkyl, aryl) positions and affords essentially single diastereomeric products with enantioselectivities higher than 95%ee in most cases. Among the bifunctional Brønsted base/H-bond catalysts examined, a known squaramide–tertiary amine catalyst and a newly prepared squaramide–tertiary amine catalyst provide the highest selectivity so far with either nitroolefins or vinyl ketones as the acceptor components. Kinetic measurements support a first-order rate dependence on both reaction partners, the donor template and the Michael acceptor, whereas competitive 1H NMR spectroscopy experiments reveal the high ability of the template for catalyst binding. [ABSTRACT FROM AUTHOR]

Abstract: Novel chiral ionic liquid stationary phases based on chiral imidazolium were prepared. The ionic liquid chiral selector was synthesized by ring opening of cyclohexene oxide with imidazole or 5,6‐dimethylbenzimidazole, and then chemically modified by different substitute groups. Chiral stationary phases were prepared by bonding to the surface of silica sphere through thioene “click” reaction. Their enantioselective separations of chiral acids were evaluated by high‐performance liquid chromatography. The retention of acid sample was related to the counterion concentration and showed a typical ion exchange process. The chiral separation abilities of chiral stationary phases were greatly influenced by the substituent group on the chiral selector as well as the mobile phase, which indicated that, besides ion exchange, other interactions such as steric hindrance, π‐π interaction, and hydrogen bonding are important for the enantioselectivity. In this report, the influence of bulk solvent components, the effects of varying concentration, and the type of the counterion as well as the proportion of acid and basic additives were investigated in detail. [ABSTRACT FROM AUTHOR]

Enantioselective inclusion of aromatic sulfoxides and nitriles was achieved in a host framework created by organic salts comprising achiral benzoic acids and a chiral primary amine (1a) derived from l‐phenylalanine. Tuning of the combined achiral acid component successfully changed the chiral recognition ability of the organic salts. The guest molecules were hydrogen‐bonded to form three‐component inclusion crystals, and the enantiomers of nitriles and sulfoxides were separated with high selectivity up to 92 and 98 % ee. As far as we know, this is the first example of the enantioseparation of non‐functionalized aromatic nitriles. [ABSTRACT FROM AUTHOR]

Abstract: A three‐dimensional π‐conjugated chiral cage with six [5]helicene units (a triple helicene cage) was synthesized for the first time. Taking advantage of the Yamamoto coupling reaction, the triflate‐substituted triple [5]helicene, a strained and preorganized precursor, was dimerized to afford the target compound. Single‐crystal X‐ray diffraction analysis revealed the unique structural features of the triple helicene cage: a cage‐shaped rigid structure with outer helical grooves and an inner chiral cavity. All‐P and all‐M enantiomers were separated successfully by HPLC over a chiral column and their chiroptical properties were characterized by circular dichroism spectra. [ABSTRACT FROM AUTHOR]

Abstract: Counterion‐induced stereocontrol is a powerful tool in organic synthesis. However, such enantiocontrol on tetrahedral ammonium cations remains challenging. Described here is the first example of using chiral anion phase‐transfer catalysis to achieve intermolecular ring‐opening of azetidiniums with excellent enantioselectivity (up to 97 % ee). Precise control over the formation and reaction of the chiral ion pair as well as inhibition of the background reaction by the biphasic system is key to the success of the reaction. [ABSTRACT FROM AUTHOR]

Abstract: A general method, using mixed ligands (here diphosphines and thiolates) is devised to turn an achiral metal cluster, Au13Cu2, into an enantiomeric pair by breaking (lowering) the overall molecular symmetry with the ligands. Using an achiral diphosphine, a racemic [Au13Cu2(DPPP)3(SPy)6]+ was prepared which crystallizes in centrosymmetric space groups. Using chiral diphosphines, enantioselective synthesis of an optically pure, enantiomeric pair of [Au13Cu2((2r,4r)/(2s,4s)‐BDPP)3(SPy)6]+ was achieved in one pot. Their circular dichroism (CD) spectra give perfect mirror images in the range of 250–500 nm with maximum anisotropy factors of 1.2×10−3. DFT calculations provided good correlations with the observed CD spectra of the enantiomers and, more importantly, revealed the origin of the chirality. Racemization studies show high stability (no racemization at 70 °C) of these chiral nanoclusters, which hold great promise in applications such as asymmetry catalysis. [ABSTRACT FROM AUTHOR]

Abstract: Bisquinolizidine alkaloids are characterized by a chiral bispidine core (3,7‐diazabicyclo[3.3.1]nonane) to which combinations of an α,N‐fused 2‐pyridone, an endo‐ or exo‐α,N‐annulated piperidin(on)e, and an exo‐allyl substituent are attached. We developed a modular “inside‐out” approach that permits access to most members of this class. Its applicability was proven in the asymmetric synthesis of 21 natural bisquinolizidine alkaloids, among them more than ten first enantioselective total syntheses. Key steps are the first successful preparation of both enantiomers of C2‐symmetric 2,6‐dioxobispidine by desymmetrization of a 2,4,6,8‐tetraoxo precursor, the construction of the α,N‐fused 2‐pyridone by using an enamine‐bromoacrylic acid strategy, and the installation of endo‐ or, optionally, exo‐annulated piperidin(on)es. [ABSTRACT FROM AUTHOR]

Abstract: The first enantioselective polyene cyclization initiated by a BINOL‐derived chiral N‐phosphoramide (NPA) catalyzed protonation of an imine is described. The ion‐pair formed between the iminium ion and chiral counter anion of the NPA plays an important role for controlling the stereochemistry of the overall transformation. This strategy offers a highly efficient approach to fused tricyclic frameworks containing three contiguous stereocenters, which are widely found in natural products. In addition, the first catalytic asymmetric total synthesis of (−)‐ferruginol was accomplished with an NPA catalyzed enantioselective polyene cyclization, as the key step for the construction of the tricyclic core, with excellent yield and enantioselectivity. [ABSTRACT FROM AUTHOR]

Abstract: Supramolecular containers featuring both high catalytic activity and high enantioselectivity represent a design challenge of practical importance. Herein, it is demonstrated that a chiral octahedral coordination cage can be constructed by using twelve enantiopure Mn(salen)‐derived dicarboxylic acids as linear linkers and six Zn4‐p‐tert‐butylsulfonylcalix[4]arene clusters as tetravalent four‐connected vertices. The porous cage features a large hydrophobic cavity (≈3944 Å3) decorated with catalytically active metallosalen species and is shown to be an efficient and recyclable asymmetric catalyst for the oxidative kinetic resolution of racemic secondary alcohols and the epoxidation of olefins with up to >99 % enantiomeric excess. The cage architecture not only prevents intermolecular deactivation and stabilizes the Mn(salen) catalysts but also encapsulates substrates and concentrates reactants in the cavity, resulting in enhanced reactivity and enantioselectivity relative to the free metallosalen catalyst. [ABSTRACT FROM AUTHOR]

We report the first desymmetrization of bisallylic amides by enantioselective bromocyclization with BINAP monoxide as a catalyst. Depending upon the substitution pattern of the alkene moieties, densely functionalized, optically active oxazoline or dihydrooxazine compounds were obtained in a highly stereoselective manner. The remaining alkene moiety was subjected to various functional group manipulations to afford a diverse array of chiral molecules with multiple stereogenic centers. [ABSTRACT FROM AUTHOR]