Catalytic Asymmetric Synthesis of Atropisomers Featuring an Aza Axis

Synthesis of Axially Chiral Compounds via Transition Metal-Catalyzed Atroposelective C-H Functionalization

ConspectusAxially chiral skeletons are prevalent in natural products and biologically important compounds, and they are widely utilized as privileged scaffolds in enantioselective catalysis. Consequently, the catalytic atroposelective synthesis of enantiopure atropisomers has garnered considerable attention. A variety of synthetic strategies involving metal catalysis or organocatalysis have been developed. Among these elegant approaches, transition metal-catalyzed enantioselective C-H activation has emerged as an atom- and step-economical strategy to streamline the construction of axially chiral compounds in recent years.In this Account, we discuss our efforts in the atroposelective synthesis of different types of axially chiral compounds, including biaryls, atropisomeric styrenes, and C-N atropisomers, via transition metal-catalyzed enantioselective C-H activation strategies. To this end, we have developed several approaches, including the chiral transient directing group (cTDG) strategy using catalytic Pd(OAc)2 and tert-leucine (Tle), as well as catalytic enantioselective systems involving Pd(II)/chiral phosphoric acid (CPA), Pd(II)/l-pyroglutamic acid (pGlu), Pd(0)/norbornene cooperative catalysis with a chiral biimidazoline (BiIM) ligand, and Co(II)/salicyloxazoline (Salox).At the outset, we successfully applied the cTDG strategy to access axially chiral biaryl aldehydes through Pd-catalyzed atroposelective C-H olefination, alkynylation, allylation, naphthylation, and alkylation. The efficacy of these methods has been demonstrated in the enantioselective synthesis of chiral aldehyde catalysts and natural products, such as TAN-1085, (+)-isochizandrin, and (+)-steganone. To facilitate the synthesis of biaryl atropisomers with diverse functionalities, we developed a novel Pd(II)/CPA catalytic system, which enables the preparation of various axially chiral quinolines, biaryl-2-amines, and atropisomeric biaryls bearing chalcogenoether units with high enantioselectivities. The Pd(II)/CPA system also allows for the synthesis of more challenging conjugated diene-based axially chiral styrenes.Nonbiaryl atropisomers, such as axially chiral styrenes and anilides, present synthetic challenges due to their conformational instability and higher degree of rotational freedom compared to their biaryl counterparts. We have addressed these challenges and achieved the highly efficient synthesis of atropisomeric styrenes and anilides using Pd(II)/pGlu and Pd(0)/norbornene/BiIM catalysis. In addition to palladium catalysis, cobalt(II)/Salox catalysis has also been developed for the construction of chiral biaryls, atropisomers with vicinal C-N and C-C stereogenic axes, remote distinct C-N diaxes, and chiral calix[4]arenes featuring both inherent and axial chirality. We anticipate that the enantioselective C-H activation strategy will find broad applications in the construction of synthetically useful axially chiral compounds.

Nickel-Catalyzed Dynamic Kinetic Asymmetric Reductive Arylation of Aldehydes with Heterobiaryl Triflates

In this context, we report a nickel-catalyzed dynamic kinetic asymmetric reductive arylation of aldehydes with racemic heterobiaryl triflates, offering a series of axially chiral heterobiaryls bearing a centrally chiral secondary alcohol moiety in a highly diastereo- and enantioselective manner. The simultaneous control of both axial and central stereogenic elements of the products lies in the stereoselective nucleophilic addition of the configurationally labile hetereobiaryl nickel complex to the formyl group of aldehydes.

Organocatalytic atroposelective de novo construction of monoaxially and 1,4-diaxially chiral fused uracils with potential antitumor activity

Atropisomers bearing multiple stereogenic axes are of increasing relevance to materials science, pharmaceuticals, and catalysis. However, the catalytic enantioselective construction of these atropisomers in a single step remains synthetically challenging. We herein report the first NHC-organocatalytic enantioselective synthesis of a new class of monoaxially and 1,4-diaxially chiral fused uracil scaffolds. Preliminary studies on the antitumor activity of selected compounds demonstrated that this new class of axially chiral uracil derivatives may have potential applications in the discovery of new lead compounds in medicinal chemistry.

P(═O)R2-Directed Asymmetric Catalytic C-H Olefination Leading to C-N Axially Chiral Targets

A novel P(═O)R2-directed asymmetric catalytic olefination has been developed, enabling efficient access to carbon-nitrogen axially chiral products with excellent yields (up to 92%) and enantioselectivity (up to 99% enantiomeric excess). The synergistic coordination of phosphine oxide functionality and l-pGlu-OH with the Pd metal center, serving as an efficient directing group and chiral ligand, was key to the success of this C-H functionalization system. The reaction demonstrated a broad substrate scope, yielding 33 distinct C-N axial products. The absolute configuration of the products was unambiguously confirmed via X-ray diffraction analysis. Additionally, three representative applications were showcased, involving reduction and oxidation to produce chiral phosphines and related derivatives. A plausible catalytic cycle mechanism has been proposed, supported by detailed experimental studies. Aggregates in the system were identified by aggregation-induced polarization experiments.

Atroposelective Synthesis of Pyridoindolones Bearing Two Remote Distinct C-N Axes through Cobalt-Catalyzed Enantioselective C-H Activation

C-N axially chiral compounds represent an important class of atropisomers that are prevalent in bioactive and material molecules. Despite recent advances in synthetic methodologies, the asymmetric construction of atropisomers featuring multiple C-N axes has been rarely explored, significantly limiting their further applications. Herein, we report a novel atroposelective synthesis of diaxially chiral pyridoindolones featuring both six-five and six-six C-N axes through cobalt-catalyzed asymmetric C-H annulation. This approach demonstrates exceptional efficiency, yielding a diverse array of chiral pyridoindolones with excellent yields and atroposelectivities (60 examples, up to >99% yield, >99% ee, and >20:1 dr). Mechanistic studies revealed that the stereochemistry of both C-N axes were generated and fixed simultaneously during the C-H cyclometalation step, along with an unexpected asymmetric amplification effect. The practicality of this protocol is further underscored by successful gram-scale syntheses and various transformations, including the formation of a chiral phosphine ligand. Notably, exceptional photoluminescence quantum yields (ΦF up to 0.99) and positive solvatochromism were observed, coupled with significant chiroptical properties, underscoring the potential applications of these compounds in organic fluorescent materials.

Atroposelective synthesis of N-N axially chiral pyrrolylamides by combined-acid catalytic Paal-Knorr reaction

A general and efficient method for the construction of enantiomerically pure N-N axially chiral pyrrolylamides by utilizing the catalytic asymmetric Paal-Knorr reaction has been developed. The key to success is the use of the binary-acid catalytic system involving the dramatic synergistic effect of a Lewis acid and a chiral phosphoric acid for achieving effective stereocontrol.

Divergent Synthesis of Axially Chiral 2-Pyranones and Fused 2-Pyridones via N-Heterocyclic Carbene-Catalyzed Atroposelective [3 + 3] Annulation

An N-heterocyclic carbene-catalyzed atroposelective [3 + 3] annulation of alkynyl acylazoliums with benzothiazole derivatives has been developed for the divergent synthesis of axially chiral triaryl 2-pyranones and fused 2-pyridones. The regioselectivity of this protocol depends on the structure of benzothiazoles with three different nucleophilic centers. The obtained axially chiral frameworks represent a new class of arylheterocycle atropisomers, which may be potentially useful in medicinal chemistry.

Asymmetric Organocatalytic 1,6-Conjugate Addition of Alkynyl 8-Methylenenaphthalen-2(8H)-one Formed In Situ: Synergistic Construction of Axial and Central Chirality

Organocatalytic enantioselective formal nucleophilic substitution reactions of α-(2-hydroxynaphthalen-8-yl)propargyl alcohols with 1-(1H-indol-3-yl)naphthalen-2-ols have been established for the first time. With the aid of a suitable chiral phosphoric acid, alkynyl 8-methylenenaphthalen-2(8H)-one was formed in situ from the corresponding α-(2-hydroxynaphthalen-8-yl)propargyl alcohol, followed by enantioselective 1,6-conjugate additions of 1-(1H-indol-3-yl)naphthalen-2-ols to afford a number of enantioenriched (Ra,Sc)-2,3-disubstituted indoles in 50-80% yields with 81-93% ee and (Sa,Sc)-2,3-disubstituted indoles in 18-40% yields with 79-96% ee. Notably, these nucleophilic substitution products were characterized by the presence of functional groups, including indole, naphthol, and alkynyl units, while exhibiting both axial and central chirality.

Biaxially chiral compounds: research and development of synthesis

With the rapid advancements in asymmetric catalysis, there is a growing need for the asymmetric selective synthesis of complex and diverse molecules with chiral axes. Axially chiral molecules are not only present in natural products and drugs but also in specialized chiral ligands and catalysts. The catalytic asymmetric synthesis of axially chiral molecules has garnered significant attention within the chemical community. To date, two asymmetric catalytic methods have been established for the synthesis of biaxially chiral molecules: transition-metal catalysis and asymmetric organocatalysis. This feature article presents a summary of the research progress made in the field of asymmetric selective synthesis of biaxially chiral molecules. This review focuses on the reaction range, limitations, and reaction mechanism of the biaxially chiral molecular synthesis method, as well as the contribution and advantages of this method in the preparation of various axially chiral compounds.

Iridium-catalyzed tandem olefination/aza-Michael reaction: rapid access to N-N functionalized hydrazides

An Ir-catalyzed tandem olefination/aza-Michael reaction of protected benzoylhydrazine derivatives with olefins under mild conditions has been developed. This method can be successfully applied to the construction of various structurally N-N-functionalized hydrazide derivatives bearing the α,β-unsaturated side chain in good to excellent yields. In particular, the deaminoprotected products can be used as potential precursors for the construction of N-N axially chiral compounds.

Organocatalytic Stereodivergent Dearomatization and N-Acylation of 2-Amino-3-subsituted Indoles

Organocatalytic chemo- and enantioselective reactions of 2-amino-3-subsituted indoles have been achieved for the first time. Via asymmetric allylic alkylation of Morita-Baylis-Hillman carbonates, organocatalytic enantioselective dearomatization of 2-amino-3-subsituted indoles afforded an array of enantioenriched 3,3-disubstituted indolin-2-imines bearing a quaternary carbon stereocenter in 34-79% yields with 61-91% ee. With Boc2O as reaction partner, the organocatalytic enantioselective N-acylation of 2-amino-3-subsituted indoles was established to furnish C-N axially chiral products in 22-98% yields with 73-92% ee.

Construction of Axially Chiral 4-Aminoquinolines by Cycloaddition and Central-to-Axial Chirality Conversion

A two-step strategy has been established for the enantioselective synthesis of 4-aminoquinolines possessing axial chirality. This approach involves a chiral phosphoric acid-catalyzed cycloaddition, followed by a DDQ oxidation step. The method offers efficient access to a variety of 1,1'-biaryl-2,2'-amino alcohol derivatives in excellent yields and enantioselectivities (up to 98% yield and 93% ee). Furthermore, the synthetic transformation of the products was also investigated.

Synthesis of Alkene Atropisomers with Multiple Stereogenic Elements via Catalytic Asymmetric Rearrangement of 3-Indolylmethanols

Catalytic enantioselective preparation of alkene atropisomers with multiple stereogenic elements and discovery of their applications have become significant but challenging issues in the scientific community due to the unique structures of this class of atropisomers. We herein report the first catalytic atroposelective preparation of cyclopentenyl[b]indoles, a new kind of alkene atropisomers, with stereogenic point and axial chirality via an unusual rearrangement reaction of 3-indolylmethanols under asymmetric organocatalysis. Notably, this novel type of alkene atropisomers have promising applications in developing chiral ligands or organocatalysts, discovering antitumor drug candidates and fluorescence imaging materials. Moreover, the theoretical calculations have elucidated the possible reaction mechanism and the non-covalent interactions to control the enantioselectivity. This approach offers a new synthetic strategy for alkene atropisomers with multiple stereogenic elements, and represents the first catalytic enantioselective rearrangement reaction of 3-indolylmethanols, which will advance the chemistry of atropisomers and chiral indole chemistry.

Synthesis of chiral systems featuring the pyrrole unit: a review

Synthetic strategies towards pyrroles within chiral frameworks are summarised, focussing on reports published 2010-2023. The synthesis of pyrroles featuring substituents bearing chiral centres are summarised, as are those whereby pyrroles are located within axially chiral systems courtesy of restricted bond rotation.

Symmetric Anion Mediated Dynamic Kinetic Asymmetric Knoevenagel Reaction for N-C and N-N Atropisomers Synthesis

A symmetric anion mediated dynamic kinetic asymmetric Knoevenagel reaction was established as a general and efficient method for accessing both N-C and N-N atropisomers. The resulting highly enantio-pure pyridine-2,6(1H,3H)-diones exhibit diverse structures and functional groups. The key to excellent regio- and remote enantiocontrol could be owed to the hydrogen bond between the enolate anion and triflamide block of the organocatalyst. This connected the enolate anion and iminium cation by a chiral backbone. The mechanism investigation via control experiments, correlation analysis, and density functional theory calculations further revealed how the stereochemical information was transferred from the catalyst into the axially chiral pyridine-2,6(1H,3H)-diones. The synthetic applications also demonstrated the reaction's potential.

Catalytic Atroposelective Synthesis of N-N Axially Chiral Indolylamides

The catalytic atroposelective synthesis of N-N axially chiral indolylamides was established via dynamic kinetic resolution, which makes use of chiral Lewis base-catalyzed asymmetric acylation of N-acylaminoindoles as a new type of platform molecule with anhydrides. By this strategy, a series of N-N axially chiral indolylamides were synthesized in overall good yields (up to 98%) with excellent enantioselectivities (up to 99% ee). Moreover, some of these N-N axially chiral indolylamides display some extent of anticancer activity, which demonstrates their potential application in medicinal chemistry. Therefore, this work has not only provided a new strategy for the synthesis of N-N axially chiral monoaryl indoles but also offered a new member of N-N axially chiral monoaryl indoles with configurational stability and promising application, thereby solving the challenges in atroposelective synthesis and application of N-N axially chiral monoaryl indoles.

Enantioconvergent and diastereoselective synthesis of atropisomeric hydrazides bearing a cyclic quaternary stereocenter through ternary catalysis

An efficient and highly enantioconvergent and diastereoselective ternary catalysis in a one-pot process is reported, which represents an integrated strategy for the synthesis of atropisomeric hydrazides with defined vicinal central and axial chirality from readily available racemic α-amino-ynones, azodicarboxylates, and Morita-Baylis-Hillman (MBH) carbonates. This method utilizes in situ-generated racemic pyrrolin-4-ones via hydroamination of racemic α-amino-ynones by AuCl catalysis as a novel and versatile C1 synthon, which engage commercially available azodicarboxylates to generate amination products in high yields and uniformly excellent enantioselectivities under the catalysis of a chiral phosphoric acid. Following amination, N-alkylation catalyzed by diastereoselective organocatalyst afforded axially chiral hydrazides with excellent diastereoselectivities (>98 : 2 dr). The synthetic utility of the amination products and axially chiral hydrazides was also demonstrated by their facile conversion to diverse molecules in high yields with excellent stereopurity. Density functional theory calculations were performed to understand the origin of diastereoselectivity.

Structural Chemistry of C-N Axially Chiral Compounds

In the last several years, atropisomers owing to the rotational restriction around a C-N single bond (C-N axially chiral compounds) have attracted significant attention in the field of synthetic organic chemistry. In particular, the highly enantioselective synthesis of various C-N axially chiral compounds and their application to asymmetric reactions have been reported by many groups. On the other hand, studies on the structural chemistry of C-N axially chiral compounds have attracted scant attention in comparison with synthetic studies. For over 25 years, our group has explored asymmetric synthesis of C-N axially chiral compounds and their synthetic application. In the course of these synthetic studies, we found several notable structural properties in relation to the C-N bond rotation and an association of enantiomers (the relationship between the rotational stability and the structure or electronic effect, the chirality-dependent halogen bond, and the self-disproportionation of enantiomers). Furthermore, on the basis of these structural properties, the development of acid-mediated molecular rotors and the synthesis of isotopic atropisomers possessing high stereochemical purity and rotational stability were achieved. Through this Perspective, I wish to make the chemistry community aware that C-N axially chiral compounds are attractive molecules from the viewpoints of both synthetic organic chemistry and structural chemistry.

Rhodium-Catalyzed Regioselective [4 + 2] Cycloaddition of Ynamines and 2-(Cyanomethyl)phenylboronates

A rhodium-catalyzed [4 + 2] cycloaddition of ynamines and 2-(cyanomethyl)phenylboronates has been developed, leading to efficient and excellent regioselective synthesis of valuable indole-linked aromatic compounds in a concise and flexible approach. Interestingly, this strategy was successful in the construction of C···N axially chiral indoles with high enantiocontrol by the introduction of a new phosphoramidite ligand (Xie-Phos).

Stable Axially Chiral Cyclohexylidenes from Catalytic Asymmetric Knoevenagel Condensation

Axially chiral cycloalkylidenes are interesting but less developed axially chiral molecules. Here, a bispidine-based chiral amine catalytic system was developed to promote efficiently the asymmetric Knoevenagel condensation of N-protected oxindoles and benzofuranones with 4-substituted cyclohexanones. A variety of alkylidenecycloalkanes with stable axial chirality were obtained in good yields and fairly good er (enantiomeric ratio). Based on the absolute configuration determination of product and DFT calculations, a possible mechanism of stereoselective induction was proposed.

Chiral amino acids: evolution in atroposelective C-H activation

This review covers the journey of chiral amino acids as ligands in atroposelective C-H bond activation/functionalization via transition metal catalysis. Herein, we intend to demonstrate how these chiral amino acids have evolved and flourished in this stimulating field. Unprotected amino acids, mono-N-protected amino acids, and di-N-protected amino acids have been devised for atroposelective C-H activation. In each section, we have briefly discuss the key successes of amino acids in the atroposelective synthesis of biaryls, heterobiaryls, and non-biaryl atropisomers and their advantages in atroposelective C-H activation.

Organocatalytic Csp2-O Amination of Quinolin-4(1H)-ones with 3-Alkynyl-3-hydroxyisoindolinones

The Brønsted acid catalytic Csp2-O amination of quinolin-4(1H)-ones with 3-alkynyl-3-hydroxyisoindolinones as animation reagents has been developed. The cascade dehydration/conjugate addition/intramolecular annulation/ring-opening reaction proceeded smoothly to afford a broad scope of aminated products with high efficiency. Furthermore, the enantioselective construction of Csp2-N atropisomers was also investigated in the presence of chiral phosphoric acid. Importantly, this work not only realized the organocatalytic Csp2-O amination of quinolin-4(1H)-ones but also laid the foundation for directly asymmetric synthesis of Csp2-N atropisomers.

Enantioselective Nickel-Catalyzed Denitrogenative Transannulation En Route to N-N Atropisomers

Nickel-catalyzed transannulation reactions triggered by the extrusion of small gaseous molecules have emerged as a powerful strategy for the efficient construction of heterocyclic compounds. However, their use in asymmetric synthesis remains challenging because of the difficulty in controlling stereo- and regioselectivity. Herein, we report the first nickel-catalyzed asymmetric synthesis of N-N atropisomers by the denitrogenative transannulation of benzotriazones with alkynes. A broad range of N-N atropisomers was obtained with excellent regio- and enantioselectivity under mild conditions. Moreover, density functional theory (DFT) calculations provided insights into the nickel-catalyzed reaction mechanism and enantioselectivity control.

Synthesis of C-N Axially Chiral N-Arylbenzo[g]indoles via a Central-to-Axial Chirality Conversion Strategy

Gold-catalyzed cascade cyclization of diynes for the synthesis of previously unexplored C-N axially chiral N-arylbenzo[g]indoles was described. The transformation was achieved via a central-to-axial chirality conversion strategy. The chiral conversion exhibited high efficiency. Besides single C-N chiral axis, N-arylbenzo[g]indoles bearing both C-N and C-C chiral axes were also afforded. The title compound derived monophosphine ligand was prepared and was evaluated in Pd-catalyzed asymmetric allylic substitutions, showing excellent chiral induction ability.

Pd-catalyzed asymmetric Larock reaction for the atroposelective synthesis of N─N chiral indoles

Atropisomeric indoles defined by a N─N axis are an important class of heterocycles in synthetic and medicinal chemistry and material sciences. However, they remain heavily underexplored due to limited synthetic methods and challenging stereocontrol over the short N─N bonds. Here, we report highly atroposelective access to N─N axially chiral indoles via the asymmetric Larock reaction. This protocol leveraged the powerful role of chiral phosphoramidite ligand to attenuate the common ligand dissociation in the original Larock reaction, forming N─N chiral indoles with excellent functional group tolerance and high enantioselectivity via palladium-catalyzed intermolecular annulation between readily available o-iodoaniline and alkynes. The multifunctionality in the prepared chiral indoles allowed diverse post-coupling synthetic transformations, affording a broad array of functionalized chiral indoles. Experimental and computational studies have been conducted to explore the reaction mechanism, elucidating the enantio-determining and rate-limiting steps.

Catalytic asymmetric construction of helicenes via transformation of biaryls

This review showcases a systematic overview of the available tools for the catalytic asymmetric transformation of biaryl substrates toward the construction of challenging enantioenriched helicenes and the conceptual aspects associated with each type of transformation. Depending on the properties of the biaryl and the nature of the process, several methodologies have been developed, including olefin metathesis, hydroarylation of alkynes, C-X (X = C, O, N) coupling, and C-H functionalization. Pioneering studies and an array of representative reactions are discussed to underscore the potential of these synthetic protocols.

Regio- and Atroposelective Ring-Opening of 1H-Benzo[4,5]oxazolopyridinones

The development of new methods for regio- and stereoselective activation of C-O bonds in ethers holds significant promise for synthetic chemistry, offering advantages in terms of environmental sustainability and economic efficiency. Moreover, the C-N atropisomers represent a fascinating and crucial chiral system, extensively found in natural products, pharmaceutical leads, and the frameworks of advanced materials. In this work, we have introduced a nickel-catalyzed regio- and enantioselective carbon-oxygen arylation reaction for atroposelective synthesis of N-arylisoquinoline-1,3(2H,4H)-diones. The high regioselectivity of C-O cleavage benefits from the high stability of the in situ formed (amido)ethenolate via oxidative addition. Additionally, the self-activation of the aryl C-O bond facilitates the reaction under mild conditions, leading to outstanding enantioselectivities. The diverse post-functionalizations of the axially chiral isoquinoline-1,3(2H,4H)-diones further highlighted the utility of this protocol in preparing valuable C-N atropisomers, including the chiral phosphine ligands.

Organocatalytic enantioselective synthesis of Csp2-N atropisomers via formal Csp2-O bond amination

Compared with well-developed construction of Csp2-Csp2 atropisomers, the synthesis of Csp2-N atropisomers remains in its infancy, which is recognized as both appealing and challenging. Herein, we achieved the first organocatalyzed asymmetric synthesis of Csp2-N atropisomers by formal Csp2-O amination. With the aid of a suitable acid, 3-alkynyl-3-hydroxyisoindolinones reacted smoothly with 1-methylnaphthalen-2-ols to afford a wide range of atropisomers by selective formation of the Csp2-N axis. Particularly, both the kinetic (Z)-products and the thermodynamic (E)-products could be selectively formed. Furthermore, the rarely used combination of two chiral Brønsted acid catalysts achieved excellent enantiocontrol, which is intriguing and unusual in organocatalysis. Based on control experiments and DFT calculations, a cascade dehydration/addition/rearrangement process was proposed. More importantly, this work provided a new plat-form for direct atroposelective construction of the chiral Csp2-N axis.

Pd-Catalyzed Asymmetric Larock Indole Synthesis to Access Axially Chiral N-Arylindoles

Larock indole synthesis is one of the most straightforward and efficient methods for the synthesis of indoles; however, there has been no asymmetric version yet for the construction of indole-based axially chiral N-arylindoles since its initial report in 1991. Herein we report the first example of an asymmetric Larock indole synthesis by employing a chiral sulfinamide phosphine (SadPhos) ligand (Ming-Phos) with palladium. It allows rapid construction of a wide range of axially chiral N-arylindole compounds in good yields up to 98:2 er. The application of this unique chiral scaffold as an organocatalyst is promising. Furthermore, a kinetic study has revealed that the alkyne migratory insertion is the rate-determining step, which has been proven by the density functional theory (DFT) calculations. Additionally, DFT studies also suggest that the N-C dihedral difference caused by the steric hindrance of the ligand contributes to enantioselectivity control.

Design and Catalytic Asymmetric Synthesis of Furan-Indole Compounds Bearing both Axial and Central Chirality

In the chemistry community, catalytic asymmetric synthesis of furan-based compounds bearing both axial and central chirality has proven to be a significant but challenging issue owing to the importance and difficulty in constructing such frameworks. In this work, we have realized the first catalytic asymmetric synthesis of five-five-membered furan-based compounds bearing both axial and central chirality via organocatalytic asymmetric (2+4) annulation of achiral furan-indoles with 2,3-indolyldimethanols with uncommon regioselectivity. By this strategy, furan-indole compounds bearing both axial and central chirality were synthesized in high yields with excellent regio-, diastereo-, and enantioselectivities. Moreover, theoretical calculations were conducted to provide an in-depth understanding of the reaction pathway, activation mode, and the origin of the selectivity.

Nitro-Enabled Atroposelective Dynamic Kinetic Resolution of 2-Arylindoles by Phase-Transfer Catalysis

This study presents the atroposelective alkylation of 2-arylindoles catalyzed by a substituted cinchonium salt as a phase-transfer catalyst. Under the optimized reaction conditions, various substrates are employed to yield products with high enantioselectivity. The presence of an ortho-nitro group at the aromatic ring is essential for high atroposelectivity, because it facilitates favorable interactions between the catalyst and substrate. The origin of the enantioselectivity reveals favorable π-π interactions for both enantiomers and unfavorable steric strains for undesired enantiomers.

Recent advances in Pd-catalyzed asymmetric cyclization reactions

Over the past few decades, there have been major developments in transition metal-catalyzed asymmetric cyclization reactions, enabling the convenient access to a wide spectrum of structurally diverse chiral carbo- and hetero-cycles, common skeletons found in fine chemicals, natural products, pharmaceuticals, agrochemicals, and materials. In particular, a plethora of enantioselective cyclization reactions have been promoted by chiral palladium catalysts owing to their outstanding features. This review aims to collect the latest advancements in enantioselective palladium-catalyzed cyclization reactions over the past eleven years, and it is organized into thirteen sections depending on the different types of transformations involved.

Catalytic Asymmetric Synthesis of N-N Biaryl Atropisomers

Atropisomers have emerged as important structural scaffolds in natural products, drug design, and asymmetric synthesis. Recently, N-N biaryl atropisomers have drawn increasing interest due to their unique structure and relatively stable axes. However, its asymmetric synthesis remains scarce compared to its well-developed C-C biaryl analogs. In this concept, we summarize the asymmetric synthesis of N-N biaryl atropisomers including N-N pyrrole-pyrrole, N-N pyrrole-indole, N-N indole-indole, and N-N indole-carbazole, during which a series synthetic strategies are highlighted. Also, a synthetic evolution is briefly reviewed and an outlook of N-N biaryl atropisomers synthesis is offered.

Enantioselective Synthesis of N-N Amide-Pyrrole Atropisomers via Paal-Knorr Reaction

The catalytic asymmetric construction of monoheteroaryl N-N axially chiral compounds and chiral five-membered aryl-based scaffolds remains challenging. Herein, we present a highly efficient enantioselective synthesis of monoheteroaryl N-N atropisomers via an asymmetric Paal-Knorr reaction, affording a diverse array of N-N amide-pyrrole atropisomers with excellent enantioselectivities. Gram-scale synthesis and post-transformations of the product demonstrated the synthesis utility of this method. Racemization experiments confirmed the configurational stability of these N-N axially chiral products. This study not only provides the first de novo cyclization example for accessing an asymmetric monoheteroaryl N-N scaffold but also offers a new member of the N-N atropisomer family with potential synthetic and medicinal applications.