Enantio- and Diastereodivergent Construction of 1,3-Nonadjacent Stereocenters Bearing Axial and Central Chirality through Synergistic Pd/Cu Catalysis

Emerging devices based on chiral nanomaterials

As advanced materials, chiral nanomaterials have recently gained vast attention due to their special geometry-based physical and chemical properties. The fast development of the related science and technology means that various devices involving polarization-based information encryption, photoelectronic and spintronic devices, 3D displays, biomedical sensors and measurement, photonic engineering, electronic engineering, solar devices, etc., been explored extensively. These fields are at their beginning, and much effort needs to be made, including improving the optical, electronic, and magnetic properties of advanced chiral nanomaterials, precisely designing materials, and developing more efficient construction methods. This review tries to offer a whole picture of these state-of-the-art conditions in these fields and offers perspectives on future development.

Discovery of Staircase Chirality through the Design of Unnatural Amino Acid Derivatives

Chirality has garnered significant attention in the scientific community since its discovery by Louis Pasteur over a century ago. It has been showing a profound impact on chemical, biomedical, and materials sciences. Significant progress has been made in controlling molecular chirality, as evidenced by the several Nobel Prizes in chemistry awarded in this area, particularly for advancements in the asymmetric catalytic synthesis of molecules with central and axial chirality. However, the exploration of new types of chirality has been largely stagnant for more than half a century, likely due to the complexity and challenges inherent in this field. In this work, we present the discovery of a novel type of chirality-staircase chirality as inspired by the design and synthesis of unnatural amino acid derivatives. The architecture of staircase chirality is characterized by 2 symmetrical phenyl rings anchored by a naphthyl pier, with the rings asymmetrically displaced due to the influence of chiral auxiliaries at their para positions. This unique staircase chiral framework has been thoroughly characterized using spectroscopic techniques, with its absolute configuration definitively confirmed by x-ray diffraction analysis. Remarkably, one of the staircase molecules exhibits 4 distinct types of chirality: central, orientational, turbo, and staircase chirality, a combination that has not been previously documented in the literature. Computational studies using density functional theory (DFT) calculations were conducted to analyze the relative energies of individual staircase isomers, and the results are in agreement with our experimental findings. We believe that this discovery will open up a new research frontier in asymmetric synthesis and catalysis, with the potential to make a substantial impact on the fields of chemistry, medicine, and materials science.

Pd/Cu Catalyzed Asymmetric Allylation for Stereodivergent Synthesis of Glutamic Acid Derivatives

A synergistic Pd/Cu catalyst system has been developed for stereodivergent transformation of Morita-Baylis-Hillman (MBH) carbonates and Schiff bases derived from simple amino acids to afford a series of optically active β-branched γ-methyleneglutamic acid derivatives with adjacent tertiary/tertiary and quaternary/tertiary stereocenters in high yields (up to 96 %) with excellent diastereo- and enantioselectivities (>20/1 dr and >99 % ee in most cases) under mild conditions. The use of SKP ligand is disclosed to be crucial for the success of the transformation, and in particular allowing the reaction to proceed at low catalyst loading (0.02 mol % for Pd and 0.08 mol % for Cu). The high efficiency of the catalysis was attributed to the formation of intimate ion pair complex A1, composed of Pd-phosphonium cation and a t-butoxide anion, which would facilitate the subsequent deprotonation and C-C coupling events. All four stereoisomers of the β-branched glutamic acid derivatives were readily prepared by permutation of the catalyst enantiomers. Synthetic utility of the methodology was exemplified by efficient synthesis of a fused pyrrolooxazolidinone with three contiguous chiral centers, highlighting the power of synergistic Pd/Cu catalysis for asymmetric allylic alkylation with MBH carbonates.

Bioinspired Synthesis of (-)-Hunterine A: Deciphering the Key Step in the Biogenetic Pathway

A concise, bioinspired, and enantioselective synthesis of (-)-hunterine A, an odd 6/7/6/6/5 pentacyclic natural product, is described. The key step in the synthesis of this complex structure is an interim-template directed 6-exo selective epoxide ring-opening reaction, which is interwoven with a hydrolysis step of the indolenine hemiaminal template to create the unusual 7-membered azepine bridge motif. Our work not only refines the previously proposed biogenetic pathway, but also reveals the possible stereochemical prerequisite of the unique skeletal rearrangement, which provides a vantage point for understanding how (-)-hunterine A is likely to be generated in nature.

Dynamic Asymmetric Diamination of Allylic Alcohols through Borrowing Hydrogen Catalysis: Diastereo-Divergent Synthesis of Tetrahydrobenzodiazepines

We present herein a catalytic enantioconvergent diamination of racemic allylic alcohols with the construction of two C-N bonds and 1,3-nonadjacent stereocenters. This iridium/chiral phosphoric acid cooperative catalytic system operates through an atom-economical borrowing hydrogen amination/aza-Michael cascade, and converts readily available phenylenediamines and racemic allylic alcohols to 1,5-tetrahydrobenzodiazepines in high enantioselectivity. An intriguing solvent-dependent switch of diastereoselectivity was also observed. Mechanistic studies suggested a dynamic kinetic resolution process involving racemization through a reversible Michael addition, making the last step of asymmetric imine reduction the enantiodetermining step of this cascade process.

Catalytic Enantioselective Friedel-Crafts Allenylation

The first enantioselective Friedel-Crafts (FC) allenylation reaction for the creation of central chirality is developed under cooperative Ir(I)/(phosphoramidite,olefin) and Lewis acid catalysis. This enantioconvergent reaction utilizes racemic allenylic alcohol as the electrophile and shows compatibility with a variety of electron-rich arenes and heteroarenes. The resulting highly enantioenriched (up to >99.5 : 0.5 e.r.) 1,1-disubstituted allenylic methanes, bearing a benzylic carbon stereocenter, are obtained with complete regiocontrol - both on (hetero)arenes as well as on the allenylic fragment. This protocol allows for the enantioselective formal introduction of a 4-carbon alkyl chain into (hetero)arenes, along with the creation of a benzylic stereocenter. Judicious synthetic elaborations not only lead to formal enantioselective FC alkylation products of less electron-rich arenes but also of substituted arenes in ortho- and even meta-selective fashion. An intramolecular version of this FC allenylation is shown to proceed with promising enantioselectivity under the same catalytic conditions. Mechanistic studies revealed the involvement of dynamic kinetic asymmetric transformation (DyKAT) of racemic allenylic alcohols in this reaction.

Rhodium-Catalyzed Trifluoromethoxylation of Allenylic Trichloroacetimidates

The first rhodium-catalyzed trifluoromethoxylation of allenylic trichloroacetimidates has been reported. The products were obtained through a procedure using trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxy source with a yield up to 76% by identifying the ligand of diene. The reaction proceeds under mild reaction conditions with excellent functional group tolerance and complete regiocontrol.

Enantioselective synthesis of molecules with multiple stereogenic elements

This review explores the fascinating world of molecules featuring multiple stereogenic elements, unraveling the different strategies designed over the years for their enantioselective synthesis. Specifically, (dynamic) kinetic resolutions, desymmetrisations and simultaneous installation of stereogenic elements exploiting either metal- or organo-catalysis are the principal approaches to efficiently create and control the three-dimensional shapes of these attractive molecules. Although most molecules presented in this review possess a stereogenic carbon atom in combination with a stereogenic axis, other combinations with helices or planes of chirality have started to emerge, as well as molecules displaying more than two different stereogenic elements.

Asymmetric Construction of Chiral 2-Azetines and Axially Chiral Tetrasubstituted Allenes Via Phosphine Catalysis

Chiral 2-azetines and allenes are highly valuable structural units in natural products and useful chemicals. However, enantioselective synthesis of both 2-azetines and allenes has been extremely challenging. Herein, we present asymmetric construction of chiral 2-azetines (70-98 % yields and up to 96 % ee) through chiral phosphine-catalyzed [2+2] annulation of yne-enones with sulfamate-derived cyclic imines. These 2-azetines were easily transformed into chiral allenes upon treatment with Et3SiH, BF3 ⋅ Et2O and water at rt for 2 minutes. Based on the above transformations, a concise one-pot synthetic procedure combining [2+2] annulation of yne-enones and sulfamate-derived cyclic imines under phosphine catalysis and sequential reduction/isomerization/ring-opening reaction through Et3SiH, BF3 ⋅ Et2O and water was thus set up, providing axially chiral tetrasubstituted allenes in satisfactory yields and enantioselectivities (56-90 % yields and up to 91 % ee).

Switchable Chemo-, Regio- and Pseudo-Stereodivergence in Palladium-Catalyzed Cycloaddition of Allenes

Here, we report a strategy enabling triple switchable chemo-, regio-, and stereodivergence in newly developed palladium-catalyzed cycloadditions of allenes. An asymmetric pseudo-stereodivergent cycloaddition of allenes bearing a primary leaving group at the α-position, where a dynamic kinetic asymmetric hydroalkoxylation of racemic unactivated allenes was the enantio-determining step, is realized, providing four stereoisomers [(Z,R), (Z,S), (E,S), and (E,R)] containing a di-substituted alkene scaffold and a stereogenic center. By tuning reaction conditions, a mechanistically distinctive cycloaddition is uncovered selectively with the same set of substrates. By switching the position of the leaving group of allenes, a cycloaddition involving an intermolecular O-attack is disclosed. Diverse mechanisms of the cycloaddition reactions of allenes enable rapid access to structurally and stereochemically diverse 3,4-dihydro-2H-1,4-benzoxazines in high efficiency and selectivity.

Rational Design and Stereodivergent Construction of Enantioenriched Tetrahydro-β-Carbolines Containing Multistereogenic Centers

Chiral tetrahydro-β-carbolines, as one of the most intriguing subtypes of indole alkaloids, have emerged as the privileged units in plenty of natural products and biologically active molecules with an impressive range of bioactive properties. However, the stereodivergent construction of these valuable skeletons containing multistereogenic centers from readily available starting materials remains very challenging, especially, in view of the introduction of an axial chirality. Herein, we developed an efficient method toward enantioenriched tetrahydro-β-carbolines with readily available tryptophan-derived aldimine esters and allylic carbonates under mild reaction conditions. The reaction proceeds in a sequential fashion involving synergistic Cu/Ir-catalyzed stereodivergent allylation and the Brønsted acid-promoted stereospecific Pictet-Spengler reaction, affording a wide range of chiral tetrahydro-β-carbolines bearing up to four stereogenic centers in good yields with excellent stereoselectivity control. When N-aryl-substituted tryptophan-derived aldimine esters were utilized, notably, a unique C-N heterobiaryl axis could be simultaneously constructed with the formation of the third point stereogenic center in the last cyclization step through dynamic kinetic resolution (DKR). Computational mechanistic studies established a plausible synergistic mechanism for dual Cu/Ir-catalyzed asymmetric allylation and the succeeding protonation-assisted Pictet-Spengler cyclization to complete the annulation. Structure-activity relationship analyses unveil the origins of stereochemistry for the building of one axis and three point stereogenic centers.

Synthesis of Chiral Endocyclic Allenes and Alkynes via Pd-Catalyzed Asymmetric Higher-Order Dipolar Cycloaddition

A Pd-catalyzed asymmetric higher-order dipolar cycloaddition between allenyl carbonates and azadienes is achieved by exploiting novel alkylidene-π-allyl-Pd dipoles. This research provides a modular platform for the synthesis of challenging chiral endocyclic allenes bearing a medium-sized heterocyclic motif and a centrally chiral stereocenter in good yields with high enantio- and diastereoselectivities (29 examples, up to 97% yield, 97:3 er and >19:1 dr). Experimental and computational studies elucidate the possible reaction mechanism and the observed stereochemical results. Based on the mechanistic understanding, a new π-propargyl-Pd dipole was designed to further extend the success of the higher order dipolar cycloaddition strategy to the synthesis of 10-membered endocyclic alkynes from propargyl carbonates and azadienes (13 examples, up to 98% yield and 94.5:5.5 er).

Nickel-Catalyzed Enantioconvergent Allenylic Amination of Allenols Activated by Hydrogen-Bonding Interaction with Methanol

The ubiquitous nature of amines in drug compounds, bioactive molecules and natural products has fueled intense interest in their synthesis. Herein, we introduce a nickel-catalyzed enantioconvergent allenylic amination of methanol-activated allenols. This protocol affords a diverse array of functionalized allenylic amines in high yields and with excellent enantioselectivities. The synthetic potential of this method is demonstrated by employing bioactive amines as nucleophiles and conducting gram-scale reactions. Furthermore, mechanistic investigations and DFT calculations elucidate the role of methanol as an activator in the nickel-catalyzed reaction, facilitating the oxidative addition of the C-O bond of allenols through hydrogen-bonding interactions. The remarkable outcomes arise from a rapid racemization of allenols enabled by the nickel catalyst and from highly enantioselective dynamic kinetic asymmetric transformation of η3-alkadienylnickel intermediates.

A General Enantioselective α-Alkyl Amino Acid Derivatives Synthesis Enabled by Cobalt-Catalyzed Reductive Addition

Enantioenriched unnatural amino acids represent a prevalent motif in organic chemistry, with profound applications in biochemistry, medicinal chemistry, and materials science. Herein, we report a cobalt-catalyzed aza-Barbier reaction of dehydroglycines with unactivated alkyl halides to afford unnatural α-amino esters with high enantioselectivity. This catalytic reductive alkylative addition protocol circumvents the use of moisture-, air-sensitive organometallic reagents, and stoichiometric chiral auxiliaries, enabling the conversion of a variety of primary, secondary, and even tertiary unactivated alkyl halides to α-alkyl-amino esters under mild conditions, thus leading to broad functional group tolerance. The expedient access to biologically active motifs demonstrates the practicality of this protocol by reducing the number of synthetic steps and enhancing the reaction efficiency.

Pd/Cu-Cocatalyzed Enantio- and Diastereodivergent Wacker-Type Dicarbofunctionalization of Unactivated Alkenes

The Wacker and Wacker-type reactions are some of the most fundamental and powerful transformations in organic chemistry for their ability to efficiently produce valuable chemicals. Remarkable progress has been achieved in asymmetric oxy/aza-Wacker-type reactions; however, asymmetric Wacker-type dicarbofunctionalization remains underdeveloped, especially for the concurrent construction of two stereocenters. Herein, we report a Pd/Cu-cocatalyzed enantio- and diastereodivergent Wacker-type dicarbofunctionalization of alkene-tethered aryl triflates with imino esters. A series of 2-indanyl motifs bearing adjacent carbon stereocenters could be easily synthesized in moderate to excellent yields and with good to excellent diastereo- and enantioselectivities (up to >20:1 dr and >99% ee). Density functional theory calculations revealed that the origin of diastereoselectivity in this Pd/Cu synergistic catalytic system is jointly determined by both the intermolecular anti-carbopalladation of alkenes and the reductive elimination processes, in accordance with the Curtin-Hammett principle.

Chemoselective and Stereoselective Allylation of Bis(alkenyl)boronates

Bis(alkenyl)boronates react with optically active Ir(π-allyl) species in a process that involves allylation of the more substituted olefin and 1,2-metalate shift of the less substituted olefin. The method constructs valuable enantioenriched tertiary allylic boronic esters with high chemoselectivity, enantioselectivity and diastereoselectivity. Allylic functionalization reactions transform the 1,3-stereodiad to 1,5- and 1,6-stereochemical relationships.

Ni/Cu Dual-Catalyzed Propargylation for the Stereodivergent Synthesis of Methohexital

The development of efficient methodologies for the controlled manufacture of specific stereoisomers bearing quaternary stereocenters has prompted advances in a variety of scientific disciplines including pharmaceutical chemistry, materials science, and chemical biology. However, complete control of the absolute and relative stereochemical configurations of alkyne derivatives remains an unmet synthetic challenge. Herein, a Ni/Cu dual-catalyzed asymmetric propargylic substitution reaction is presented to produce propargylated products with all-carbon quaternary stereocenters in high yields with significant diastereo- and enantioselectivities (up to >20:1 dr, >99% ee). The synthesis of all stereochemical variants of methohexital, a widely used sedative-hypnotic drug, exemplifies the efficacy of dual-catalyzed stereodivergent propargylation.

Stereodivergent access to non-natural α-amino acids via enantio- and Z/E-selective catalysis

The precise control of Z and E configurations of the carbon-carbon double bond in alkene synthesis has long been a fundamental challenge in synthetic chemistry, even more pronounced when simultaneously striving to achieve enantioselectivity [(Z,R), (Z,S), (E,R), (E,S)]. Moreover, enantiopure non-natural α-amino acids are highly sought after in organic and medicinal chemistry. In this study, we report a ligand-controlled stereodivergent synthesis of non-natural α-quaternary amino acids bearing trisubstituted alkene moieties in high yields with excellent enantioselectivity and Z/E selectivities. This success is achieved through a palladium/copper-cocatalyzed three-component assembly of readily available aryl iodides, allenes, and aldimine esters by simply tuning the chiral ligands of the palladium and copper catalysts.

Stereodivergent Construction of 1,5/1,7-Nonadjacent Tetrasubstituted Stereocenters Enabled by Pd/Cu-Cocatalyzed Asymmetric Heck Cascade Reaction

The construction of chiral motifs containing nonadjacent stereocenters in an enantio- and diastereoselective manner has long been a challenging task in synthetic chemistry, especially with respect to their stereodivergent synthesis. Herein, we describe a protocol that enables the enantio- and diastereoselective construction of 1,5/1,7-nonadjacent tetrasubstituted stereocenters through a Pd/Cu-cocatalyzed Heck cascade reaction. Notably, a C=C bond relay strategy involving the shift of the π-allyl palladium intermediate was successfully applied in the asymmetric construction of 1,7-nonadjacent stereocenters. The current method allows for the efficient preparation of chiral molecules bearing two privileged scaffolds, oxindoles and non-natural α-amino acids, with good functional group tolerance. The full complement of the four stereoisomers of products bearing 1,5/1,7-nonadjacent stereocenters could be readily accessed by a simple combination of two chiral metal catalysts with different enantiomers.

Copper/ruthenium relay catalysis enables 1,6-double chiral inductions with stereodivergence

The dual catalysis strategy is an efficient and powerful tool to fulfill the stereodivergent synthesis of stereoisomeric products from the same set of starting materials. Great attention has been given to the construction of chiral compounds with two contiguous stereocenters. However, the synthesis of two remote noncontiguous stereocenters is more challenging and is less developed, despite the high demand for synthetic tactics. We herein developed an unprecedented example of the stereodivergent preparation of synthetically useful and biologically important chiral ζ-hydroxy amino ester derivatives containing remote 1,6-noncontiguous stereocenters and a unique β,γ-unsaturation moiety. This cascade dehydrogenation/1,6-Michael addition/hydrogenation protocol between readily-available ketoimine esters and racemic branched dienyl carbinols was rationally realized with bimetallic copper/ruthenium relay catalysis. The key features of the process were atom economy, step economy, and redox-neutrality. All four stereoisomers of chiral ζ-hydroxy amino ester derivatives were easily achieved by the orthogonal permutations of a chiral copper catalyst and chiral ruthenium catalyst. Importantly, a much more challenging stereodivergent synthesis of all eight stereoisomers of chiral peptide products containing three remote stereocenters was accomplished with excellent results through the cooperation of two chiral catalyst pairs and substrate enantiomers.

Ligand-Controlled, Nickel-Catalyzed Stereodivergent Construction of 1,3-Nonadjacent Stereocenters

In contrast to the asymmetric synthesis of molecules with a single stereocenter or 1,2-adjacent stereocenters, the simultaneous construction of acyclic 1,3-nonadjacent stereocenters via a single catalyst in an enantioselective and diastereoselective manner remains a formidable challenge. Here, we demonstrate the enantioselective and diastereodivergent construction of 1,3-nonadjacent stereocenters through Ni-catalyzed reductive cyclization/cross-coupling of alkene-tethered aryl bromides and α-bromoamides, which represents the major remaining stereochemical challenge of cyclization/difunctionalization of alkenes. Using Ming-Phos as ligand, a diverse set of oxindoles containing 1,3-nonadjacent stereocenters were obtained with high levels of enantio- and diastereoselectivity. Mechanistic experiments and density functional theory calculations indicate that magnesium salt plays a key role in controlling the diastereoselectivity. Furthermore, another set of complementary stereoisomeric products were constructed from the same set of starting materials using Ph-Phox as ligand.

Bimetallic Ru/Ru-Catalyzed Asymmetric One-Pot Sequential Hydrogenations for the Stereodivergent Synthesis of Chiral Lactones

Asymmetric sequential hydrogenations of α-methylene γ- or δ-keto carboxylic acids are established in one-pot using a bimetallic Ru/Ru catalyst system, achieving the stereodivergent synthesis of all four stereoisomers of both chiral γ- and δ-lactones with two non-vicinal carbon stereocenters in high yields (up to 99%) and with excellent stereoselectivities (up to >99% ee and >20:1 dr). The compatibility of the two chiral Ru catalyst systems is investigated in detail, and it is found that the basicity of the reaction system plays a key role in the sequential hydrogenation processes. The protocol can be performed on a gram-scale with a low catalyst loading (up to 11000 S/C) and the resulting products allow for many transformations, particularly for the synthesis of several key intermediates useful for the preparation of chiral drugs and natural products.

Synergistic Palladium/Copper-Catalyzed 1,4-Difunctionalization of 1,3-Dienes for Stereodivergent Construction of 1,5-Nonadjacent Stereocenters

The construction of two distal stereocenters through a single catalytic process is of great interest in organic synthesis. While there are some successful reports regarding stereodivergent preparation of 1,3- or 1,4-stereocenters, the more challenged 1,5-nonadjacent stereocenters have never been achieved in a stereodivergent fashion. Herein we describe a synergistic palladium/copper catalysis for 1,4-difunctionalization reactions of 1,3-dienes, providing access to 1,5-nonadjacent quaternary stereocenters. Because each of the two catalysts separately controlled one of the newly formed stereocenters, stereodivergent synthesis of all four diastereomers of the products could readily be achieved simply by choosing an appropriate combination of chiral catalysts. Experimental and computational studies supported a mechanism involving a Heck/Tsuji-Trost cascade reaction, and the origins of the stereoselectivity were elucidated.

Synergistic Pd/Cu-Catalyzed 1,5-Double Chiral Inductions

Much attention has been focused on the catalytic asymmetric creation of single chiral centers or two adjacent stereocenters. However, the asymmetric construction of two nonadjacent stereocenters is of significant importance but is challenging because of the lack of remote chiral induction models. Herein, based on a C═C bond relay strategy, we report a synergistic Pd/Cu-catalyzed 1,5-double chiral induction model. All four stereoisomers of the target products bearing 1,5-nonadjacent stereocenters involving both allenyl axial and central chirality could be obtained divergently by simply changing the combination of two chiral catalysts with different configurations. Control experiments and DFT calculations reveal a novel mechanism involving 1,5-oxidative addition, contra-thermodynamic η3-allyl palladium shift, and conjugate nucleophilic substitution, which play crucial roles in the control of reactivity, regio-, enantio-, and diastereoselectivity. It is expected that this C═C bond relay strategy may provide a general protocol for the asymmetric synthesis of structural motifs bearing two distant stereocenters.

Pd-Catalyzed Enantioselective Creation of All-Carbon Quaternary Center with 2,3-Allenylic Carbonates

Enantioselective construction of all-carbon quaternary centers has been achieved via the palladium-catalyzed highly enantioselective allenylation of oxindoles with 2,3-allenylic carbonates to afford a variety of optically active allene products, which contain oxindole units with different functional groups, in high ee. The corresponding synthetic applications have also been demonstrated.

Copper/Ruthenium Relay Catalysis for Stereodivergent Access to δ-Hydroxy α-Amino Acids and Small Peptides

An atom- and step-economical and redox-neutral cascade reaction enabled by asymmetric bimetallic relay catalysis by merging a ruthenium-catalyzed asymmetric borrowing-hydrogen reaction with copper-catalyzed asymmetric Michael addition has been realized. A variety of highly functionalized 2-amino-5-hydroxyvaleric acid esters or peptides bearing 1,4-non-adjacent stereogenic centers have been prepared in high yields with excellent enantio- and diastereoselectivity. Judicious selection and rational modification of the Ru catalysts with careful tuning of the reaction conditions played a pivotal role in stereoselectivity control as well as attenuating undesired α-epimerization, thus enabling a full complement of all four stereoisomers that were otherwise inaccessible in previous work. Concise asymmetric stereodivergent synthesis of the key intermediates for biologically important chiral molecules further showcases the synthetic utility of this methodology.

Synergistic Catalysis Involving Palladium for Stereodivergent Csp3-Csp3 Coupling Reactions

ConspectusTransition-metal-catalyzed coupling reactions of dienes (such as 1,3-dienes, alkoxyallenes, and aminoallenes) with carbon nucleophiles have proven to be a highly effective method for creating Csp3-Csp3 bonds. These reactions have perfect atom economy and typically occur under mild reaction conditions. By using chiral metal complexes as catalysts, it is possible to create enantioenriched molecules bearing allylic stereocenters with high enantioselectivities. However, challenges arise when Csp3-Csp3 bonds bearing two vicinal stereocenters are constructed through this type of coupling reaction. Due to the inherent diastereoselectivities, only the kinetically favored diastereoisomers (either the syn- or anti-product) are usually obtained through the transition-metal catalyst system. Achieving complementary stereoisomers with high selectivity, which require complete control of both absolute and relative configurations of multiple chiral centers in a single chemical transformation, is usually impossible.Over the past decade, significant advancements have been made in stereodivergent synthesis. Notably, iridium-related synergistic catalysis has been rapidly developed for stereodivergent allylic alkylation reactions. However, these systems were limited to using allylic alcohol derivatives as electrophilic partners. Finding ways to extend the use of synergistic catalysis to other types of stereodivergent reactions is a crucial issue that needs to be addressed.In 2019, we reported the first palladium-mediated synergistic system for the stereodivergent Csp3-Csp3 coupling between 1,3-dienes and aldimine esters. Lately, this strategy has proven successful in accessing stereodivergent coupling with diverse substrate patterns. In this Account, we will summarize our laboratory's efforts in developing a range of palladium-involved synergistic catalysis systems for the stereodivergent Csp3-Csp3 coupling reactions of dienes. We discovered several synergistic catalysis systems, including Pd/Cu(Ag), Pd/amine, Pd/Lewis base, and Pd/PTC. Additionally, we developed diverse dienes, such as 1,3-dienes, alkoxyallenes, and aminoallenes, to serve as suitable coupling partners for stereodivergent coupling. These processes provide an efficient method for constructing a range of chiral scaffolds bearing vicinal stereocenters. Density functional theory (DFT) calculations have been performed to elucidate the reaction mechanism and to rationalize the origins of the stereochemistry for some of the synergistic catalyst systems. Finally, the synthetic application of these methods has been demonstrated in the concise total synthesis of a number of natural products and bioactive molecules. It is anticipated that an increasing number of chemists will join in the research on stereodivergent Csp3-Csp3 coupling reactions and contribute to more elegant examples in this area. We believe future development will further push the boundary of asymmetric catalysis and find more innovative applications soon for synthesizing complex chiral molecules.

Dual-Catalyzed Stereodivergent Electrooxidative Homocoupling of Benzoxazolyl Acetate

The development of a reliable strategy for stereodivergent radical reactions that allows convenient access to all stereoisomers of homocoupling adducts with multiple stereogenic centers remains an unmet goal in organic synthesis. Herein, we describe a dual-catalyzed electrooxidative C(sp3)-H/C(sp3)-H homocoupling with complete absolute and relative stereocontrol for the synthesis of molecules with contiguous quaternary stereocenters in a general and predictable manner. The stereodivergent electrooxidative homocoupling reaction is achieved by synergistically utilizing two distinct chiral catalysts that convert identical racemic substrates into inherently distinctive reactive chiral intermediates, dictate enantioselective radical addition, and allow access to the full complement of stereoisomeric products via simple catalyst permutation. The successful execution of the dual-electrocatalytic strategy programmed via electrooxidative activation provides a significant conceptual advantage and will serve as a useful foundation for further research into cooperative stereocontrolled radical transformations and diversity-oriented synthesis.

Core Structure-Oriented Asymmetric α-Allenylic Alkylation of Amino Acid Esters Enabled by Chiral Aldehyde/Palladium Catalysis

Aiming at the reported chiral synthons leading to manzacidins A and D, here we report a highly efficient catalytic asymmetric α-allenylic alkylation reaction of NH2-unprotected amino acid esters that is promoted by combined chiral aldehyde/palladium catalysis. Fifty examples of unnatural α,α-disubstituted amino acid esters are reported with good-to-excellent yields and stereoselectivities. Based on this methodology, a key intermediate leading to manzacidin C and its other three stereoisomers is prepared accordingly.

Enantioselective synthesis of 3-(N-indolyl)quinolines containing axial and central chiralities

Quinoline and indole are important core structures in biologically active compounds and materials. Atropisomeric biaryls consisting of quinoline and indole are a unique class of axially chiral molecules. We report herein enantioselective synthesis of 3-(N-indolyl)quinolines having both C-N axial chirality and carbon central chirality by a photoredox Minisci-type addition reaction catalyzed by a chiral lithium phosphate/Ir-photoredox complex. The catalytic system enabled access to a unique class of 3-(N-indolyl)quinolines with high chemo-, regio-, and stereoselectivities in good yields through the appropriate choice of an acid catalyst and a photocatalyst. This is the first example of the synthesis of 3-(N-indolyl)quinoline atropisomers in a highly enantioselective manner.

Modular access to chiral bridged piperidine-γ-butyrolactones via catalytic asymmetric allylation/aza-Prins cyclization/lactonization sequences

Chiral functionalized piperidine and lactone heterocycles are widely spread in natural products and drug candidates with promising pharmacological properties. However, there remains no general asymmetric methodologies that enable rapid assemble both critical biologically important units into one three-dimensional chiral molecule. Herein, we describe a straightforward relay strategy for the construction of enantioenriched bridged piperidine-γ-butyrolactone skeletons incorporating three skipped stereocenters via asymmetric allylic alkylation and aza-Prins cyclization/lactonization sequences. The excellent enantioselectivity control in asymmetric allylation with the simplest allylic precursor is enabled by the synergistic Cu/Ir-catalyzed protocol; the success of aza-Prins cyclization/lactonization can be attributed to the pivotal role of the ester substituent, which acts as a preferential intramolecular nucleophile to terminate the aza-Prins intermediacy of piperid-4-yl cation species. The resulting chiral piperidine-γ-butyrolactone bridged-heterocyclic products show impressive preliminary biological activities against a panel of cancer cell lines.

Stereodivergent synthesis of α-fluoro α-azaaryl γ-butyrolactones via cooperative copper and iridium catalysis

The development of stereodivergent synthetic methods to access all four stereoisomers of biologically important α-fluoro γ-butyrolactones containing vicinal stereocenters is of great importance and poses a formidable challenge owing to ring strain and steric hindrance. Herein, a novel asymmetric [3+2] annulation of α-fluoro α-azaaryl acetates with vinylethylene carbonate was successfully developed through Cu/Ir-catalyzed cascade allylic alkylation/lactonization, affording a variety of enantioenriched α-fluoro γ-butyrolactones bearing vicinal stereogenic centers with high reaction efficiency and excellent levels of both stereoselectivity and regioselectivity (up to 98% yield, generally >20:1 dr and >99% ee). Notably, all four stereoisomers of these pharmaceutically valuable molecules could be accessed individually via simple permutations of two enantiomeric catalysts. In addition, other azaaryl acetates bearing α-methyl, α-chlorine or α-phenyl group were tolerated well in this transformation. Reaction mechanistic investigations were conducted to explore the process of this bimetallic catalysis based on the results of reaction intermediates, isotopic labelling experiments, and kinetic studies.

Asymmetric Synthesis of Chiral 1,2-Bis(Boronic) Esters Featuring Acyclic, Non-Adjacent 1,3-Stereocenters

The construction of acyclic, non-adjacent 1,3-stereogenic centers, prevalent motifs in drugs and bioactive molecules, has been a long-standing synthetic challenge due to acyclic nucleophiles being distant from the chiral environment. In this study, we successfully synthesized highly valuable 1,2-bis(boronic) esters featuring acyclic and nonadjacent 1,3-stereocenters. Notably, this reaction selectively produces migratory coupling products rather than alternative deborylative allylation or direct allylation byproducts. This approach introduces a new activation mode for selective transformations of gem-diborylmethane in asymmetric catalysis. Additionally, we found that other gem-diborylalkanes, previously challenging due to steric hindrance, also successfully participated in this reaction. The incorporation of 1,2-bis(boryl)alkenes facilitated the diversification of the alkenyl and two boron moieties in our target compounds, thereby enabling access to a broad array of versatile molecules. DFT calculations were performed to elucidate the reaction mechanism and shed light on the factors responsible for the observed excellent enantioselectivity and diastereoselectivity. These were determined to arise from ligand-substrate steric repulsions in the syn-addition transition state.

Nickel-Catalyzed Enantioselective Synthesis of Dienyl Sulfoxide

Sulfoxides are widely used in the pharmaceutical industry and as ligands in asymmetric catalysis. However, the efficient asymmetric synthesis of this structural motif remains limited. In this study, we disclosed a Ni-catalyzed enantioconvergent reaction that utilizes both racemic allenyl carbonates and β-sulfinyl esters. Our method employs cheap and more sustainable Ni(II) as a precatalyst and successfully overcomes the challenging poisoning effect and instability of sulfenate generated in situ. This enables the synthesis of a series of dienyl sulfoxides with enantioselectivity of up to 98 % ee. The product exhibits tremendous potential in various applications, including diastereoselective Diels-Alder reactions, coordination with transition metals, and incorporation into medicinal compounds, among others. Using a combination of experimental and computational methods, we have uncovered an interesting associated outersphere mechanism that contrasts with conventional mechanisms commonly observed in asymmetric transition metal catalysis.

Enantio- and Diastereoselective Copper-Catalyzed Synthesis of Chiral Aziridines with Vicinal Tetrasubstituted Stereocenters

A Cu-catalyzed coupling of cyclic imino esters with 2H-azirines has been developed to synthesize novel optically active aziridines in high yields with excellent levels of diastereo- and enantioselectivities under mild conditions. This novel protocol features a broad substrate scope and good functional group compatibility, and it enriches the existing reaction type of rapid synthesis of optically active aziridines bearing vicinal tetrasubstituted stereogenic carbon centers.

Dispersion Interactions in Asymmetric Induction for Constructing Vicinal Stereogenic Centers

ConspectusVicinal stereogenic centers are prevalent structural motifs of primary functional relevance in natural products and bioactive molecules. The quest for the rapid and controllable construction of vicinal stereogenic centers stands as a frontier endeavor in asymmetric organic synthesis. Over the past decade, stereodivergent synthesis has been intensely researched within the realm of bimetallic catalysis, aiming at establishing novel transition-metal dual-catalytic reactions that efficiently generate all stereochemical combinations of multichiral molecules from identical starting materials, thus offering new opportunities toward rapid complexity building and diversity-oriented chiral compound library generation. In this Account, we summarize our recent advancements in computational investigations of stereodivergent asymmetric allylic alkylation, an important reaction class heavily studied for the purpose of constructing vicinal stereogenic centers. Our discussions focus on synergistic bimetallic catalysis for the syntheses of α,α-disubstituted α-amino acids and cascade allylation/cyclization toward enantiomerically enriched indole-containing heterocycles. We describe our series of studies that converge in establishing the molecular mechanism of asymmetric induction for chiral copper-azomethine ylide, a nucleophile that holds widespread utility and is characterized by a distinctive, sterically biased surrounding enveloping the prochiral center. Notably, our studies revealed that attacks at the prochiral site by allylmetal species are significantly favored by dispersion attraction from one face (-PPh2) but blocked by steric repulsion and associated structural distortions on the opposite face (oxazoline), therefore building up a multimodal and highly robust face-selective stereoinduction. We showcase how a suite of systematic computational analyses generates precise atomistic insights into a number of systems of relevance. We also discuss how the same methodologies can be applied to chiral intermediates with shared interaction patterns, including the rhodium-Josiphos catalyst in asymmetric hydrogenation to create two continuous stereocenters. In the selectivity-controlling migratory insertion step, our computational models unveiled that the reaction is favored by ligand-substrate dispersion attraction on the -PPh2 side and hindered by steric repulsion on the opposite -PtBu2 side. These noncovalent interactions along with the distal ligand-auxiliary structural distortions enable strictly oriented three-dimensional stereoinduction. Our analysis of ligand-substrate dispersion interactions and steric effects in competing pathways highlights certain interaction-level similarities between PHOX-type and Josiphos-type ligands in asymmetric induction. In summary, this Account underscores the foundational significance and broad applicability of nonbonded dispersion interactions in asymmetric inductions for the construction of vicinal stereogenic centers. We envisage that the computational methodologies employed in these studies will shift toward a paradigm of interaction-based rational molecular and reaction design.

Palladium-catalyzed stereoselective construction of chiral allenes bearing nonadjacent axial and two central chirality

It is challenging to enantioselectively construct molecules bearing multiple nonadjacent stereocenters, in contrast to those bearing a single stereocenter or adjacent stereocenters. Herein, we report an enantio- and diastereoselective synthesis of substituted chiral allenes with nonadjacent axial and two central chiral centers through a combination of retro-oxa-Michael addition and palladium-catalyzed asymmetric allenylic alkylation. This methodology exhibits good functional-group compatibility, and the corresponding allenylic alkylated compounds, including flavonoid frameworks, are obtained with good yields and diastereoselectivities and excellent enantioselectivities (all >95% ee). Furthermore, the scalability of the current synthetic protocol was proven by performing a gram-scale reaction.

Diastereodivergent Catalysis

Alongside enantioselective catalysis, synthetic chemists are often confronted by the challenge of achieving catalyst control over the relative configuration to stereodivergently access desired diastereomers. Typically, these approaches iteratively or simultaneously control multiple stereogenic units for which dual catalytic methods comprising sequential, relay, and synergistic catalysis emerged as particularly efficient strategies. In this Perspective, the benefits and challenges of catalyst-controlled diastereodivergence in the construction of carbon stereocenters are discussed on the basis of illustrative examples. The concepts are then transferred to diastereodivergent catalysis for atropisomeric systems with twofold and higher-order stereogenicity as well as diastereodivergent catalyst control over E- and Z-configured alkenes.

Ligand-Controlled Diastereodivergency in Propargylic Alkylation of Vinylogous Aza-Enamines: Construction of 1,3-Stereocenters

The first diastereodivergent propargylic alkylation reaction is developed. This Cu(I)-catalyzed formal decarboxylative [4+2] cycloaddition between ethynyl benzoxazinanone and vinylogous aza-enamine delivers each diastereomer of tetrahydroquinoline derivatives, bearing 1,3-stereocenters, using either i-Pr-Pybox or BINAP as the ligand under otherwise identical reaction conditions. This is the first application of vinylogous aza-enamines in a transition metal-catalyzed transformation and the first example of the creation of 1,3-stereocenters in a propargylic substitution reaction.

Chemodivergence in Pd-catalyzed desymmetrization of allenes: enantioselective [4+3] cycloaddition, desymmetric allenylic substitution and enynylation

A class of prochiral allenylic di-electrophiles have been introduced for the first time as three-atom synthons in cycloadditions, and a new type of [4+3] cycloaddition involving transition metal-catalyzed enantioselective sequential allenylic substitution has been successfully developed, enabling challenging seven-membered exocyclic axially chiral allenes to be accessed in good yields with good enantioselectivity. Through the addition of a catalytic amount of ortho-aminoanilines or ortho-aminophenols, the racemization of the [4+3] cycloaddition products is effectively suppressed. Mechanistic studies reveal that elusive Pd-catalyzed enantioselective intramolecular allenylic substitution rather than intermolecular allenylic substitution is the enantio-determining step in this cycloaddition. By tuning the ligands, a Pd-catalyzed enantioselective desymmetric allenylic substitution leading to linear axially chiral tri-substituted allenes or a Pd-catalyzed tandem desymmetric allenylic substitution/β-vinylic hydrogen elimination (formal enynylation) leading to multi-functionalized 1,3-enynes is achieved chemodivergently.

Pseudo-Diastereodivergent Synthesis of Chiral Fluorenes Bearing Bis-1,3-Nonadjacent Stereogenic Centers via Organocatalytic Desymmetrization of meso-Epoxides

We report an enantio- and diastereodivergent synthesis of enantioenriched fluorenes bearing bis-1,3-nonadjacent stereocenters with broad substrate scope and high enantioselectivity (up to 99% ee) under low catalyst loading (0.1 mol %). The key to the success of this method is the pseudo-diastereodivergent desymmetrization of stereoisomers of meso-epoxides enabled by the same organocatalyst. Furthermore, some of the chiral fluorenes obtained exhibit high fluorescence quantum yields (up to 76.6%), as evidenced by photophysical properties studies.

Rhodium-catalyzed enantioselective and diastereodivergent access to diaxially chiral heterocycles

N-N axially chiral biaryls represent a rarely explored class of atropisomers. Reported herein is construction of diverse classes of diaxially chiral biaryls containing N-N and C-N/C-C diaxes in distal positions in excellent enantioselectivity and diastereoselectivity. The N-N chiral axis in the products provides a handle toward solvent-driven diastereodivergence, as has been realized in the coupling of a large scope of benzamides and sterically hindered alkynes, affording diaxes in complementary diastereoselectivity. The diastereodivergence has been elucidated by computational studies which revealed that the hexafluoroisopropanol (HFIP) solvent molecule participated in an unusual manner as a solvent as well as a ligand and switched the sequence of two competing elementary steps, resulting in switch of the stereoselectivity of the alkyne insertion and inversion of the configuration of the C-C axis. Further cleavage of the N-directing group in the diaxial chiral products transforms the diastereodivergence to enantiodivergence.

Silver/chiral pyrrolidinopyridine relay catalytic cycloisomerization/(2 + 3) cycloadditions of enynamides to asymmetrically synthesize bispirocyclopentenes as PDE1B inhibitors

Significant progress has been made in asymmetric synthesis through the use of transition metal catalysts combined with Lewis bases. However, the use of a dual catalytic system involving 4-aminopyridine and transition metal has received little attention. Here we show a metal/Lewis base relay catalytic system featuring silver acetate and a modified chiral pyrrolidinopyridine (PPY). It was successfully applied in the cycloisomerization/(2 + 3) cycloaddition reaction of enynamides. Bispirocyclopentene pyrazolone products could be efficiently synthesized in a stereoselective and economical manner (up to >19:1 dr, 99.5:0.5 er). Transformations of the product could access stereodivergent diastereoisomers and densely functionalized polycyclic derivatives. Mechanistic studies illustrated the relay catalytic model and the origin of the uncommon chemoselectivity. In subsequent bioassays, the products containing a privileged drug-like scaffold exhibited isoform-selective phosphodiesterase 1 (PDE1) inhibitory activity in vitro. The optimal lead compound displayed a good therapeutic effect for ameliorating pulmonary fibrosis via inhibiting PDE1 in vivo.

Palladium-catalyzed asymmetric allenylic alkylation: construction of multiple chiral thiochromanone derivatives

The development of a new strategy for the construction of chiral cyclic sulfide-containing multiple stereogenic centers is highly desirable. Herein, by the combination of base-promoted retro-sulfa-Michael addition and palladium-catalyzed asymmetric allenylic alkylation, the streamlined synthesis of chiral thiochromanones containing two central chiralities (including a quaternary stereogenic center) and an axial chirality (allene unit) was successfully realized with up to 98% yield, 49.0 : 1 dr and >99% ee.

Asymmetric α-allylic allenylation of β-ketocarbonyls and aldehydes by synergistic Pd/chiral primary amine catalysis

We herein describe an asymmetric α-allylic allenylation of β-ketocarbonyls and aldehydes with 1,3-enynes. A synergistic chiral primary amine/Pd catalyst was identified to facilitate the utilization of 1,3-enynes as atom-economic and achiral allene precursors. The synergistic catalysis enables the construction of all-carbon quaternary centers-tethered allenes bearing non-adjacent 1,3-axial central stereogenic centers in high level of diastereo- and enantio-selectivity. By switching the configurations of ligands and aminocatalysts, diastereodivergence can be achieved and any of the four diastereoisomers can be accessed in high diastereo- and enantio- selectivity.

Synergistic Li/Li Bimetallic System for the Asymmetric Synthesis of Antituberculosis Drug TBAJ-587

TBAJ-587, an analogue of the antituberculosis drug bedaquiline (BDQ), bearing a diarylquinoline skeleton retains the high bacterial potency, is less toxic, and has a better pharmacokinetic profile than the parent molecule, which has entered phase I clinical trials. In contrast to its fascinating bioactivity, however, the highly efficient synthesis of this molecule is still an unsolved challenge. Herein, the first asymmetric synthesis of TBAJ-587 based on a synergistic Li/Li bimetallic system is reported. The product could be obtained in an excellent yield of 90% and an enantiomeric ratio (er) of 80:20. Furthermore, the reaction could be conducted on a 5 g scale, and the product was obtained with 99.9:0.1 er after a simple recrystallization. The realization of this protocol will greatly aid the demand for clinical drug production.

Enantio- and diastereodivergent synthesis of fused indolizines enabled by synergistic Cu/Ir catalysis

Highly diastereo-/enantioselective assembly of 2,3-fused indolizine derivatives could be easily available through a cascade allylation/Friedel-Crafts type reaction enabled by a synergistic Cu/Ir catalysis. This designed protocol provides an unprecedented and facile route to enantioenriched indolizines bearing three stereogenic centers in moderate to high yields with excellent stereoselective control, which also featured broad substrate generality. Remarkably, four stereoisomers of the 2,3-fused indolizine products could be efficiently constructed in a predictable manner through the pairwise combination of copper and iridium catalysts. The synthetic utility of this method was readily elaborated by a gram-scale reaction, and synthetic transformations to other important chiral indolizine derivatives. Quantum mechanical explorations constructed a plausible synergetic catalytic cycle, revealed the origins of stereodivergence, and rationalized the protonation-stimulated stereoselective Friedel-Crafts type cyclization to form the indolizine products.

Palladium-Catalyzed Stereoselective Construction of 1,3-Stereocenters Displaying Axial and Central Chirality via Asymmetric Alkylations

The concurrent construction of 1,3-stereocenters remains a challenge. Herein, we report the development of stereoselective union of a point chiral center with allenyl axial chirality in 1,3-position by Pd-catalyzed asymmetric allenylic alkylation between racemic allenyl carbonates and indanone-derived β-ketoesters. Various target products bearing a broad range of functional groups were afforded in high yield (up to 99%) with excellent enantioselectivities (up to 98% ee) and good diastereoselectivities (up to 13:1 dr).

Reactivity of vinylidene-π-allyl palladium(II) species

The reactivity of a new type of organometallic intermediate, vinylidene-π-allyl palladium species, has been demonstrated: the reaction between 4-alken-2-ynyl carbonates and stabilized carbon nucleophiles afforded functionalized 1,2,3,-butatriene compounds in moderate to high yields and excellent regioselectivities.

Stereodivergent Construction of 1,3-Chiral Centers via Tandem Asymmetric Conjugate Addition and Allylic Substitution Reaction

Herein, we report a synthesis of cyclohexanones bearing multi-continuous stereocenters by combining copper-catalyzed asymmetric conjugate addition of dialkylzinc reagents to cyclic enones with iridium-catalyzed asymmetric allylic substitution reaction. Good to excellent yields, diastereoselectivity and enantioselectivity can be obtained. Unlike the stereodivergent construction of adjacent stereocenters (1,2-position) reported in the literature, the current reaction can achieve the stereodivergent construction of nonadjacent stereocenters (1,3-position) by a proper combination of two chiral catalysts with different enantiomers.