Stereodivergent Allylation of Azaaryl Acetamides and Acetates by Synergistic Iridium and Copper Catalysis

Chiral phosphoric acid-catalyzed asymmetric epoxidation of alkenyl aza-heteroarenes using hydrogen peroxide

The synthesis of chiral α-azaheteroaryl oxiranes via enantioselective catalysis is a formidable challenge due to the required complex stereoselectivity and diverse N-heterocyclic structures. These compounds play a crucial role in developing bioactive molecules, where precise chirality significantly influences biological activity. Here we show that using chiral phosphoric acid as a catalyst, our method efficiently addresses these challenges. This technique not only achieves high enantio- and diastereoselectivity but also demonstrates superior chemo- and stereocontrol during the epoxidation of alkenyl aza-heteroarenes. Our approach leverages a synergistic blend of electrostatic and hydrogen-bonding interactions, enabling the effective activation of both substrates and hydrogen peroxide. The resulting chiral oxiranes exhibit enhanced diversity and functionality, aiding the construction of complex chiral azaaryl compounds with contiguous stereocenters. Kinetic and density functional theory studies elucidate the mechanism, highlighting chiral phosphoric acid's pivotal role in this intricate enantioselective process.

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.

Stereodivergent Synthesis of Spiroaminals via Chiral Bifunctional Hydrogen Bonding Organocatalysis

Spiroaminals represent novel structural motifs prevalent in diverse natural products and biologically active molecules. Achieving their enantioselective synthesis is a highly desirable and challenging task in synthetic endeavors due to their intricate molecular frameworks. Herein, we accomplished the first stereodivergent construction of spiroaminals using chiral bifunctional organocatalyzed intramolecular 1,2-addition followed by an oxa-Michael addition cascade in a high atom and step economical pathway. A proper modulation of the cinchona-derived squaramide catalysts efficiently provided access to all the possible stereoisomers with high yield, diastereoselectivity, and excellent enantioselectivity while displaying a broad substrate tolerance. Additionally, we validated the scalability of the reaction and demonstrated the synthesis of variable spiroaminal scaffolds, confirming the viability of our protocol.

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.

Asymmetric Construction of Carbon-Fluorine Quaternary Stereogenic Centers via Synergistic Pd/Cu Catalysis

We developed an asymmetric decarboxylative allylic alkylation of vinylethylene carbonates with α-fluoro pyridinyl acetates through a synergistic palladium/copper catalysis. This protocol provides chiral allylic alcohol with carbon-fluorine quaternary stereogenic centers in good yield with good enantioselectivities and excellent regioselectivities. The utility of this approach was further demonstrated via a gram-scale experiment and derivatizations of the product.

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.

Stereodivergent Synthesis of All Stereoisomers of 2,3-Disubstituted δ-Lactam Derivatives via Organocatalytic Cascade Reactions and Base-Induced Epimerization

A protocol was developed to achieve stereodivergent synthesis of stereoisomers of δ-lactam bearing vicinal chiral centers. Organocatalytic cascade reactions were employed to produce the target products as the kinetic products, which exhibited remarkable enantioselectivities. In the presence of DBU, the kinetic product underwent epimerization to form a thermodynamically more stable diastereomer without loss in enantioselectivity. By simply switching the chiral organocatalyst and its enantiomer, we can efficiently obtain four stereoisomers with high enantioselectivities.

Enantio- and Diastereodivergent N-Heterocyclic Carbene/Nickel Dual-Catalyzed Umpolung Propargylic Substitutions of Enals

The creation of full stereoisomers of an organic compound comprising multiple contiguous stereocenters with simultaneous control over both relative and absolute configurations remains a significant challenge in synthetic chemistry. Using a cooperative catalysis strategy, we established an N-heterocyclic carbene/nickel-catalyzed enantio- and diastereodivergent propargylation reaction to access 3,3'-disubstituted oxindoles, enabling the incorporation of internal alkyne functionality and the introduction of a single quaternary or vicinal quaternary/tertiary stereogenic center. By selecting the appropriate combination of catalyst chirality, all four potential stereoisomers of α-quaternary propargylated oxindoles were synthesized in a predictable and precise way with remarkable yields, diastereoselectivities, and enantioselectivities from identical starting materials. The synthetic utility of this method was demonstrated in the concise asymmetric total synthesis of (-)-debromoflustramine B and (-)-C(β-Me)-debromoflustramine B.

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.

Bifunctional Iminophosphorane Catalyzed Amide Enolization for Enantioselective Cyclohexadienone Desymmetrization

The organocatalytic enolization of 2-arylacetamides, followed by an enantioselective intramolecular conjugate addition to tethered 2,5-cyclohexadienones, yielding 3D fused N-heterocycles, is described. The transformation represents the first strong activating group-free activation of carboxamides via α-C-H deprotonation in a metal-free, catalytic, and enantioselective reaction, and is achieved by employing a bifunctional iminophosphorane (BIMP) superbase.

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.

Desymmetrization of Geminal Difluoromethylenes using a Palladium/Copper/Lithium Ternary System for the Stereodivergent Synthesis of Fluorinated Amino Acids

Fluorinated amino acids and related peptides/proteins have been found widespread applications in pharmaceutical and agricultural compounds. However, strategies for introducing a C-F bond into amino acids in an enantioselective manner are still limited and no such asymmetric catalysis strategy has been reported. Herein, we have successfully developed a Pd/Cu/Li ternary system for stereodivergent synthesis of chiral fluorinated amino acids. This method involves a sequential desymmetrization of geminal difluoromethylenes and allylic substitution with amino acid Schiff bases via Pd/Li and Pd/Cu dual activation, respectively. A series of non-natural amino acids bearing a chiral allylic/benzylic fluorine motif are easily synthesized in high yields with excellent regio-, diastereo-, and enantioselectivities (up to >20 : 1 dr and >99 % ee). A density functional theory (DFT) study revealed the F-Cu interaction of the allylic substrate and the Cu catalyst significantly influence the stereoselectivity.

Iridium-Catalyzed Enantioselective Alkene Hydroalkylation via a Heteroaryl-Directed Enolization-Decarboxylation Sequence

Upon exposure to a cationic Ir(I)-complex modified with the chiral diphosphine DuanPhos, hydroalkylations of styrenes and α-olefins with diverse heteroaryl tert-butyl acetates occur with complete branched selectivity and very high enantioselectivity. The initial adducts undergo acid promoted decarboxylation in situ to provide alkylated heteroarenes possessing defined β-stereocenters. The processes are postulated to proceed via a stereodefined chiral Ir-enolate, which arises upon heteroarene directed enolization of the heteroaryl acetate precursor. The method can be classified as an enantioselective decarboxylative C(sp3)-C(sp3) cross-coupling.

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.

Synergistic Ni/Pd Catalysis for Asymmetric Allylic Alkylation of 2-Acyl Imidazoles

The asymmetric α-allylation of α-aryl-substituted 2-acetyl imidazoles synergistically catalyzed by Ni/Pd catalysts has been developed. In this process, the nickel-bisoxazoline complex activates the enolate of an acetyl imidazole, which then reacts with a π-allyl palladium electrophile generated from an allyl alcohol derivative by a palladium-based catalyst. A broad scope of substrates was suitable for this reaction. The utility of this method was demonstrated by a gram-scale reaction and subsequent elaboration of the allylation products.

Iridium-Catalyzed Asymmetric Allylic Substitution Reaction of 4-Hydroxypyran-2-one

Pyranones have raised great concerns owing to their considerable applications in a variety of sectors. However, the development of direct asymmetric allylation of 4-hydroxypyran-2-ones is still restricted. Herein, we present an effective iridium-catalyzed asymmetric functionalization technique for the synthesis of 4-hydroxypyran-2-one derivatives over direct and efficient catalytic asymmetric Friedel-Crafts-type allylation by using allyl alcohols. The allylation products could be obtained with good to high yields (up to 96%) and excellent enantioselectivities (>99% ee). Therefore, the disclosed technique provides a new asymmetric synthetic strategy to explore pyranone derivatives in depth, thus providing an interesting approach for global application and further utilization in organic synthesis and pharmaceutical chemistry.

Multimetallic-Catalyzed C-C Bond-Forming Reactions: From Serendipity to Strategy

The use of two or more metal catalysts in a reaction is a powerful synthetic strategy to access complex targets efficiently and selectively from simple starting materials. While capable of uniting distinct reactivities, the principles governing multimetallic catalysis are not always intuitive, making the discovery and optimization of new reactions challenging. Here, we outline our perspective on the design elements of multimetallic catalysis using precedent from well-documented C-C bond-forming reactions. These strategies provide insight into the synergy of metal catalysts and compatibility of the individual components of a reaction. Advantages and limitations are discussed to promote further development of the field.

Iridium-Catalyzed Chemo-, Diastereo-, and Enantioselective Allyl-Allyl Coupling: Accessing All Four Stereoisomers of (E)-1-Boryl-Substituted 1,5-Dienes by Chirality Pairing

Here, we report a highly chemo-, diastereo-, and enantioselective allyl-allyl coupling between branched allyl alcohols and α-silyl-substituted allylboronate esters, catalyzed by a chiral iridium complex. The α-silyl-substituted allylboronate esters can be chemoselectively coupled with allyl electrophiles, affording a diverse set of enantioenriched (E)-1-boryl-substituted 1,5-dienes in good yields, with excellent stereoselectivity. By permuting the chiral iridium catalysts and the substrates, we efficiently and selectively obtained all four stereoisomers bearing two consecutive chiral centers. Mechanistic studies via density functional theory calculations revealed the origins of the diastereo- and chemoselectivities, indicating the pivotal roles of the steric interaction, the β-silicon effect, and a rapid desilylation process. Additional synthetic modifications for preparing a variety of enantioenriched compounds containing contiguous chiral centers are also included.

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.

Stereodivergent Synthesis of Allenes with α,β-Adjacent Central Chiralities Empowered by Synergistic Pd/Cu Catalysis

The stereodivergent synthesis of allene compounds bearing α,β-adjacent central chiralities has been realized via the Pd/Cu-catalyzed dynamic kinetic asymmetric alkylation of racemic allenylic esters. The matched reactivity of bimetallic catalytic system enables the challenging reaction of racemic aryl-substituted allenylic acetates with sterically crowded aldimine esters smoothly under mild reaction conditions. Various chiral non-natural amino acids bearing a terminal allenyl group are easily synthesized in high yields and with excellent diastereo- and enantioselectivities (up to >20 : 1 dr, >99 % ee). Importantly, all four stereoisomers of the product can be readily accessed by switching the configurations of the two chiral metal catalysts. Furthermore, the easy interconversion between the uncommon η³ -butadienyl palladium intermediate featuring a weak C=C/Pd coordination bond and a stable Csp² -Pd bond is beneficial for the dynamic kinetic asymmetric transformation process (DyKAT).

Diastereodivergent Desymmetric Annulation to Access Spirooxindoles: Chemical Probes for Mitosis

Spirooxindoles have emerged as promising architectures for engineering biologically active compounds. The diastereodivergent construction of unique scaffolds of this type with full control of continuous chiral centers including an all-carbon quaternary stereogenic center is yet to be developed. Here, we report an unprecedented diastereodivergent desymmetric [3 + 3] annulation of oxabicyclic alkenes with enals enabled by N-heterocyclic carbene (NHC)/Rh cooperative catalysis, leading to a series of enantiomerically enriched spirooxindole lactones with excellent enantioselectivities (up to >99% ee) and diastereoselectivities (up to >95:5 dr). The combined catalyst system comprises a rhodium complex that controls the configuration at the electrophilic carbon and an NHC catalyst that controls the configuration at the nucleophilic oxindole-containing carbon; thus, four stereoisomers of the spirooxindole products can be readily obtained simply by switching the configurations of the two chiral catalysts. Transformations of the chiral spirooxindoles delivered synthetically useful compounds. Importantly, those chiral spirooxindoles arrested mammalian cells in mitosis and exhibited potent antiproliferative activities against HeLa cells. Significantly, both absolute and relative configurations exert prominent effects on the bioactivities, underscoring great importance of catalytic asymmetric diastereodivergent synthesis beyond creating useful tools for the exploration of structure-activity relationships.

Boron-Catalyzed α-Functionalizations of Carboxylic Acids

Catalytic, chemoselective, and asymmetric α-functionalizations of carboxylic acids promise up-grading simple feedstock materials to value-added functional molecules, as well as late-stage structural diversifications of multifunctional molecules, such as drugs and their leads. In this personal account, we describe boron-catalyzed α-functionalizations of carboxylic acids developed in our group (five reaction types). The reversible boron carboxylate formation is key to the acidification of the α-protons and enolization using mild organic bases, allowing for chemoselective and asymmetric bond formations of carboxylic acids. The ligand effects on reactivity and stereoselectivity, substrate scopes, and mechanistic insights are summarized.

Stereodivergent Construction of Csp3 -Csp3 Bonds Bearing Vicinal Stereocenters by Synergistic Palladium and Phase-Transfer Catalysis

Synergistic catalysis has emerged as one of the most powerful tools for stereodivergent formation of Csp³ -Csp³ bonds bearing vicinal stereocenters. Despite the many successes that have been achieved in this field, stereodivergent Csp³ -Csp³ coupling reactions involving stabilized nucleophiles remain challenging because of the competing single-catalysis pathway. Herein, we report a synergistic palladium/phase-transfer catalyst system that enables diastereodivergent Csp³ -Csp³ coupling reactions of 1,3-dienes with stabilized nucleophile oxindoles. Both the syn and anti coupling products, bearing quaternary and tertiary vicinal stereocenters, could be selectively produced in good yields with high enantio- and diastereoselectivities. Non-covalent activation of the stabilized nucleophile via chiral ion pair in a biphasic system is a crucial success factor in achieving diastereodivergence.

Dual-Catalytic Enantioselective Allylation of N-(Heteroaromatic-methyl)imine Derivatives

We report the dual-catalytic enantioselective allylic alkylation of 2-(pyridylmethyl)amine-derived ketimines with allylic carbonates. The reaction proceeds under mild reaction conditions to generate α-amino heteroaryl benzylamine stereocenters in good yield and enantioselectivity. Enantioselectivity is achieved through the use of a copper catalyst modified with chiral bisphosphine ligand (2S,4S)-bis(diphenylphosphino)pentane.

Cobalt(III)-Catalyzed and DMSO-Involved Allylation of 1,3-Dicarbonyl Compounds with Alkenes

Cobalt(III)-catalyzed allylation of 1,3-dicarbonyl compounds has been reported with in situ generated allyl reagents from alkenes and dimethyl sulfoxide (DMSO). This novel protocol enables a high regio- and stereoselective access for a broad range of allyl 1,3-dicarbonyl compounds. In the transformation, DMSO plays the role of a C1 source, and it incorporates with alkenes to form the allyl reagent allylic methyl thioether. Moreover, a multiple-step pathway has been proposed to rationalize the mechanism study, which involves silver-mediated coupling, Co(III)-catalyzed π-allylation, and intermolecular nucleophilic substitution.

Stereodivergent dehydrative allylation of β-keto esters using a Ru/Pd synergistic catalyst

α-Alkylation of a β-keto ester is a frequently used reaction for carbon–carbon bond formation. However, extension to a stereoselective reaction remains a significant challenge, because the product easily racemizes under acidic or basic conditions. Here, we report a hybrid system consisting of Pd and Ru complexes that catalyzes the asymmetric dehydrative condensation between cinnamyl-type allylic alcohols and β-keto esters. α-Non-substituted β-keto ester can be allylated to afford an α-mono-substituted product with high regio-, diastereo-, and enantioselectivity. No epimerization occurs owing to the nearly neutral conditions, which is achieved by a rapid proton transfer from Pd-enolate formation to Ru π-allyl complex formation. Four diastereomers can be synthesized on demand by changing the stereochemistry of the Pd or Ru complex. Eight stereoisomers with three adjacent stereogenic centers can be synthesized by employing diastereoselective reduction of the ketone in the products. The formal synthesis of (+)-pancratistatin demonstrates the utility of the reaction.

α-Alkylation of β-keto esters is a frequently used reaction for carbon–carbon bond formation, but a general, stereoselective version of this reaction is challenging to realize. Here, the authors report a combined ruthenium and palladium catalytic system for the asymmetric dehydrative condensation between cinnamyl-type allylic alcohols and β-keto esters.

Dual Rh(II)/Pd(0) Relay Catalysis Involving Sigmatropic Rearrangement Using N-Sulfonyl Triazoles and 2-Hydroxymethylallyl Carbonates

Dual Rh(II)/Pd(0) relay catalysis of N-sulfonyl triazoles and 2-hydroxymethylallyl carbonates has been developed, which affords N-sulfonyl pyrrolidines in moderate to good yields with high diastereoselectivities. The reaction proceeds via a relay mechanism involving O-H insertion onto the α-imino Rh(II)-carbene, [3,3]-sigmatropic rearrangement, dipole formation through Pd(0)-catalyzed decarboxylation, and intramolecular N-allylation, leading to the formation of multiple bonds in a one-pot operation.

Ir and NHC Dual Chiral Synergetic Catalysis: Mechanism and Stereoselectivity in γ-Butyrolactone Formation

Cooperative dual catalysis is a powerful strategy for achieving unique reactivity by combining catalysts with orthogonal modes of action. This approach allows for independent control of the absolute and relative stereochemistry of the product. Despite its potential utility, the combination of N-heterocyclic carbene (NHC) organocatalysis and transition metal catalysis has remained a formidable challenge as NHCs readily coordinate metal centers. This characteristic also makes it difficult to rationalize or predict the stereochemical outcomes of these reactions. Herein, we use quantum mechanical calculations to investigate formation of γ-butyrolactones from aldehydes and allyl cyclic carbonates by means of an NHC organocatalyst and an iridium catalyst. Stereoconvergent activation of the racemic allyl cyclic carbonate forms an Ir-π-allyl intermediate and activation of an unsaturated aldehyde forms an NHC enolate, the latter of which is rate-limiting. Union of the two fragments leads to stereodetermining C-C bond formation and ultimately ring closure to generate the product lactone. Notably, CO2 loss occurs after formation of the C-C bond and Et3NH+ plays a key role in stabilizing carboxylate intermediates and in facilitating proton transfer to form the NHC enolate. The computed pathways agree with the experimental findings in terms of the absolute configuration, the enantiomer excess, and the different diastereomers seen with the (R)- and (S)-spiro-phosphoramidite combined with the NHC catalyst. Calculations reveal the lowest energy pathway includes both an NHC ligand and a phosphoramidite ligand on the iridium center. However, the stereochemical features of this Ir-bound NHC were found to not contribute to the selectivity of the process.

Diastereodivergent Aldol-Type Coupling of Alkoxyallenes with Pentafluorophenyl Esters Enabled by Synergistic Palladium/Chiral Lewis Base Catalysis

As a fundamental and synthetically useful C-C bond formation reaction, the aldol reaction is one of the most versatile transformations in organic synthesis. However, despite extensive research on asymmetric versions of the reaction, a unified method for stereoselective access to the complementary syn and anti diastereomeric products remains to be developed. In this study, we developed a synergistic palladium/chiral Lewis base system that overcomes the inherent diastereoselectivity bias of aldol reactions and, as a result, allowed us to achieve the first diastereodivergent coupling reactions of alkoxyallenes with pentafluorophenol esters. Computational studies suggest a mechanism involving an intermolecular protonative hydropalladation pathway rather than a palladium-hydride migratory insertion pathway. The origin of the stereochemistry for this synergistic catalysis system is rationalized by DFT calculations.

Stereodivergent Synthesis of Enantioenriched α-Deuterated α-Amino Acids via Cascade Cu(I)-Catalyzed H-D Exchange and Dual Cu- and Ir-Catalyzed Allylation

A one-pot Cu-mediated H-D exchange with inexpensive heavy water as the deuterium source, followed by Cu- and Ir-catalyzed stereodivergent allylic alkylation, has been developed, providing efficient access to enantioenriched α-deuterium-labeled α-amino acids from readily available glycine imine esters in a high yield with excellent stereoselectivity. High deuterium enrichment, exquisite regioselectivity, precise stereoselectivity control, and operationally convenient procedures make this protocol appealing for the preparation of highly synthetically useful α-deuterated α-amino acids.

Enantioselective Synthesis of Spiroketals and Spiroaminals via Gold and Iridium Sequential Catalysis

The enantioselective cascade reaction between racemic 2-(1-hydroxyallyl)phenols and alkynols/alkynamides was realized by using a gold and iridium sequential catalytic system. In this procedure, the in situ generated exocyclic vinyl ethers or enamides undergo the asymmetric allylation/spiroketalization with π-ally-Ir amphiphilic species, which provides an efficient and straightforward access to spiroketals and spiroaminals with excellent enantioselectivities. Moreover, racemic 2-(1-hydroxyallyl)anilines were also suitable in this reaction along with a kinetic resolution process, affording enantioenriched spiroaminals and 2-(1-hydroxyallyl)anilines in good yields. The synthetic utility of this method has been demonstrated by efficient enantioselective synthesis of the analogue of Paecilospirone.

Stereodivergent synthesis of enantioenriched azepino[3,4,5-cd]-indoles via cooperative Cu/Ir-catalyzed asymmetric allylic alkylation and intramolecular Friedel-Crafts reaction

The development of enantioselective annulation reactions using readily available substrates for the construction of structurally and stereochemically diverse heterocycles is a compelling topic in diversity-oriented synthesis. Herein, we report efficient catalytic asymmetric formal 1,3-dipolar (3 + 4) cycloadditions of azomethine ylides with 4-indolyl allylic carbonates for the construction of azepino[3,4,5-cd]-indoles fused with a challenging seven-membered N-heterocycle, a frequently occurring tricyclic indole scaffold in bioactive compounds and pharmaceuticals. Through cooperative Cu/Ir-catalyzed asymmetric allylic alkylation followed by intramolecular Friedel-Crafts reaction, an array of azepino[3,4,5-cd]-indoles were obtained in good yields with excellent diastereo-/enantioselective control. More importantly, the full stereodivergence of this transformation was established via synergistic catalysis followed by acid-promoted epimerization, and up to eight stereoisomers of the cycloadducts bearing three stereogenic centers could be predictably achieved from the same set of starting materials for the first time. Quantum mechanical computations established a plausible mechanism for the synergistic Cu/Ir catalysis to stereodivergently introduce two vicinal stereocenters whose stereochemical information is remotely delivered across the fused azepine ring to control the third chiral center. Epimerization of the last center involves protonation-enabled reversal of the thermodynamically controlled relative configuration.