Synergistic Dual Transition Metal Catalysis

Dirhodium-Palladium Dual-Catalyzed [1 + 1 + 3] Annulation to Heterocycles Using Primary Amines or H2O as the Heteroatom Sources

The ever-increasing demand in chemical biology and medicinal research requires the development of new synthetic methods for the rapid construction of libraries of heterocycles from simple raw materials. In this context, the utilization of primary amines or H2O as the simple N- or O-sources in the assembly of a heterocyclic ring skeleton is highly desirable from the viewpoint of atom- and step-economy. Herein, we describe a highly efficient three-component reaction of diazo, allylic diacetates, and commercially available anilines (or H2O) to access structurally diverse pyrrolidine and tetrahydrofuran derivatives. This formal [1 + 1 + 3] annulation reaction features high efficiency, good yields, and broad functional group compatibility, making it a versatile and robust platform for the (formal) synthesis of several important bioactive molecules. Mechanistic studies suggested that the dirhodium-palladium bimetallic relay catalysis should play a key role in the successive steps of the current reaction, including sequential carbene insertion into the X-H bond and double allylic substitutions, thus allowing for building up molecular complexity from these simple raw materials.

One-Pot Domino Catalysis to Construct Alkyl/Aryl Pyrroles Initiated by Pd-TMM Annulation of Unactivated Imines

Herein, a one-pot domino catalyzed three-component process is described, which is initiated by a palladium/zinc cooperatively catalyzed cycloaddition between trimethylenemethane (TMM) and unactivated alkyl/aryl imines, followed by one-pot isomerization and Zn(OTf)2-catalyzed DDQ oxidation, furnishing valuable substituted pyrroles. We disclose that the palladium/zinc cooperative catalysis affords a dual-Zn(OTf)2-stabilized azapalladacycle, wherein the Pd-N bond is polarized by Zn(OTf)2, facilitating a unique outer-sphere allylic amination. Moreover, subsequent DDQ dehydrogenation can be feasibly promoted by zinc catalysis.

Diastereoselective and Enantioselective Hydrophosphinylations of Conjugated Enynes, Allenes and Dienes via Synergistic Pd/Co Catalysis

Different from the reported work focusing on the construction of single P- or C-stereocenter via hydrophosphinylation of unsaturated carbon bonds, the highly diastereo- and enantioselective hydrophosphinylation reaction of allenes, conjugated enynes and 1,3-dienes is achieved via a designed Pd/Co dual catalysis and newly modified masked phosphinylating reagent. A series of allyl motifs bearing both a tertiary C- and P-stereocenter are prepared in generally good yields, >20 : 1 dr, >20 : 1 rr and 99 % ee. The unprecedented diastereo- and enantioselective hydrophosphinylation of 1,3-enynes is established to generate skeletons containing both a P-stereocenter and a nonadjacent chiral axis. The first stereodivergent hydrophosphinylation reaction is also developed to achieve all four P-containing stereoisomers. The present protocol features the use of only 3-minutes reaction time and 0.1 % catalyst, and with the observation of up to 730 TON. A set of mechanistic studies reveal the necessity and roles of two metal catalysts and corroborate the designed synergistic process.

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.

Diastereodivergence in catalytic asymmetric conjugate addition of carbon nucleophiles

Catalytic asymmetric conjugate additions of carbon nucleophiles have emerged as a potent tool for constructing multi-stereogenic molecules with precise stereochemical control. This review explores the concept of diastereodivergence in such reactions, focusing on strategies to achieve selective access to diverse diastereomeric products upon carbon-carbon bond formation. Drawing from a rich array of examples, we delve into key approaches for controlling the stereochemical outcome of these transformations, including alteration of alkene geometry, fine-tuning of reaction parameters, synergistic catalysis, and isomerization of conjugate adducts. Additionally, we highlight the iterative strategies for conjugate additions, showcasing their potential for diastereodivergent synthesis of methyl-branched stereocenters in 1,3-relationships. By presenting a concentrated overview of this significant topic, this review aims to provide valuable insights into the design and execution of stereodivergent catalytic conjugate additions, offering new avenues for advancing stereoselective synthesis and structural diversity in organic synthesis.

Direct Synthesis of Saturated Alcohols from Conjugated Ketones Using NaBH4 and Catalytic Amount of CuCN in Ethanol: Additive Catalysis with a Lithium Salt or a Sodium Salt

A direct, efficient, and highly chemoselective synthesis of saturated alcohols through one-pot sequential 1,4- and 1,2-reduction of cyclic and acyclic conjugated ketones is reported. The saturated alcohols are obtained in very good yields using sodium borohydride (NaBH4) as a reducing agent and a catalytic amount of copper(I) cyanide (CuCN) in ethanol as a green solvent. This nontoxic solvent significantly favors full 1,4-reduction, as opposed to methanol. Selectivity is further enhanced by the combination of two additives (a lithium salt or a sodium salt, such as NaI).

Pd/Cu-Cocatalyzed Asymmetric Cascade Heck/Tsuji-Trost Reaction to Access Non-natural Tryptophans

A Pd-catalyzed asymmetric Heck cascade reaction involving the intramolecular carbopalladation of unsaturated hydrocarbons, followed by nucleophilic trapping of the resulting palladium species, is a powerful approach for constructing chiral N-heterocycles. However, the use of prochiral nucleophiles in these reactions remains significantly underexplored. Herein, we report a novel Pd/Cu catalytic system for the asymmetric cascade Heck/Tsuji-Trost reaction of allenamides and aldimine esters. This robust method allows for the rapid synthesis of a wide range of enantiopure non-natural α-substituted tryptophans in high yields (up to 99% yield) with excellent enantioselectivities (up to 98% ee). Additionally, the synthetic utility of this protocol is demonstrated through scale-up experiments and diverse valuable transformations.

Synergistic Rh(II)- and Zn(II)-Catalyzed [3 + 3] Annulation of Diazoenals and α-Hydroxy Ketones for the Direct Synthesis of 2H-Pyrans, A Gateway Toward γ-Pyrones

A new synergistic Rh(II)/Zn(II)-catalyzed [3 + 3] annulation has been developed between diazoenals and α-hydroxy ketones enabling the direct synthesis of 4-formyl-2H-pyrans. The reaction involves the formation of protic oxonium ylides from highly electrophilic Rh-enalcarbenoids followed by Zn-templated regioselective intramolecular aldol condensation. Subsequent investigations demonstrated that 4-formyl-2H-pyrans are unique precursors of γ-pyrones. The γ-pyrones were obtained via Et3N-mediated oxidative deformylation. Further, the triflic-acid-promoted double Schmidt reaction of 4-formyl-2H-pyrans provides synthetically important carboxamide-substituted 4-cyano 2H-pyrans.

Forging 1,1'-Bicyclopropenyls by Synergistic Au/Ag Dual-Catalyzed Cyclopropenyl Cross-Coupling

1,1'-Bicyclopropenyl is a constitutional isomer of benzene comprising two coupled cyclopropene units with the endocyclic double bonds in conjugation. Due to the intrinsic high strain energy, it remains a long-standing challenge to prepare 1,1'-bicyclopropenyl derivatives, particularly multisubstituted, nonsymmetrical ones, in an efficient and modular manner. Herein a straightforward Au/Ag bimetallic-catalyzed cyclopropenyl cross-coupling has been developed, providing a robust and versatile strategy for the rapid assembly of symmetrical and unsymmetrical 1,1'-bicyclopropenyl derivatives from cyclopropenyl benziodoxoles (CpBXs) and terminal cyclopropenes. Advantages of this strategy include tolerance to a wide range of synthetically useful functional groups, mild reaction conditions, and a simple catalytic system. The obtained 1,1'-bicyclopropenyl derivatives were shown to be valuable synthetic intermediates through selective downstream manipulations.

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.

Synergistic Pd/Ni Dual-Catalyzed Cross-Coupling of Azaaryl Acetates with gem-Difluorinated Cyclopropanes

We herein report the development of a novel Pd/Ni dual-catalyzed ring-opening functionalization of gem-difluorinated cyclopropanes (gem-F2CPs) with azaaryl acetates. This bimetallic catalytic strategy streamlines the diversity-oriented synthesis (DOS) of α-quaternary 2-fluoroallylic azaaryl acetates with features of a broad scope and excellent functional group tolerance, which enables the efficient late-stage transformation of natural product-derived gem-F2CPs. The resulting α-quaternary azaaryl acetates could serve as a valuable platform to prepare other different fluoroallylic azaaryl scaffolds.

Synergistic Homogeneous Asymmetric Cu Catalysis with Pd Nanoparticle Catalysis in Stereoselective Coupling of Alkynes with Aldimine Esters

Understanding the nature of a transition-metal-catalyzed process, including catalyst evolution and the real active species, is rather challenging yet of great importance for the rational design and development of novel catalysts, and this is even more difficult for a bimetallic catalytic system. Pd(0)/carboxylic acid combined system-catalyzed allylic alkylation reaction of alkynes has been used as an atom-economical protocol for the synthesis of allylic products. However, the asymmetric version of this reaction is still rather limited, and the in-depth understanding of the nature of active Pd species is still elusive. Herein we report an enantioselective coupling between readily available aldimine esters and alkynes using a synergistic Cu/Pd catalyst system, affording a diverse set of α-quaternary allyl amino ester derivatives in good yields with excellent enantioselectivities. Mechanistic studies indicated that it is most likely a synergistic asymmetric molecular Cu catalysis with Pd nanoparticle catalysis. The Pd catalyst precursor is transformed to soluble Pd nanoparticles in situ, which are responsible for activating the alkyne to an electrophilic allylic Pd intermediate, while the chiral Cu complex of the aldimine ester enolate provides chiral induction and works in synergy with the Pd nanoparticles.

Selective Functionalization of Alkenes and Alkynes by Dinuclear Manganese Catalysts

ConspectusAlkenes and alkynes are fundamental building blocks in organic synthesis due to their commercial availability, bench-stability, and easy preparation. Selective functionalization of alkenes and alkynes is a crucial step for the synthesis of value-added compounds. Precise control over these reactions allows efficient construction of complex molecules with new functionalities. In recent decades, second- and third-row precious transition metal catalysts (palladium, platinum, rhodium, ruthenium) have been pivotal in the development of metal-catalyzed synthetic methodology. These metals exhibit excellent catalytic activity and selectivity, enabling efficient synthesis of functionalized organic molecules. However, recovery and reuse of precious metals have long been a challenge in this field. In recent years, exploration of earth-abundant metal-catalyzed organic reactions has interested both academic and industrial researchers. The development of such catalytic systems offers a promising approach to overcome the limitations of precious metal catalysts. For example, manganese is the third most naturally abundant transition metal with minimal toxicity and excellent biocompatibility. It exhibits good catalytic activity in several organic reactions, including C-H bond functionalization, selective reduction, and radical reactions. This Account outlines our recent progress in dinuclear manganese catalysis for selective functionalization of alkenes and alkynes. We have established the elementary manganese(I)-catalysis in transmetalation with R-B(OH)2. This finding has enabled us to apply the catalyst for the selective 1,2-difunctionalization of structurally diverse alkenes and alkynes. Mechanistic studies suggest a double manganese center synergistic activation model, as superior to Mn(CO)5Br in some cases. In addition, we have developed a ligand-tuned metalloradical strategy of dinuclear manganese catalysts (Mn2(CO)10), bridging the gap between the organometallics and radical chemistry, highlighting the unique radical functionalization of alkenes. Interestingly, using the same starting materials, different ligands can deliver completely different products. Meanwhile, a cooperative catalysis strategy involving manganese and other catalysts (e.g., cobalt, iminium) has also been developed and is briefly discussed. For manganese/iminium synergistic catalysis, a new mechanism for migratory insertion and demetalization-isomerization in synergistic HOMO-LUMO activation was disclosed. This strategy expands the application of low-valent manganese catalysts for enantioselective C-C bond-forming reactions. New reaction discovery is outpacing mechanism studies for dinuclear manganese catalysis, and future studies with time-resolved spectroscopy will improve understanding of the mechanism. Based on these intriguing findings, the precise functionalization of alkenes and alkynes by dinuclear manganese catalysts will expedite a novel activation model to enable late-stage functionalization of complex molecules.

Optimization of Metal-Support Cooperation for Boosting the Performance of Supported Gold Catalysts for the Borylation of C-O and C-N Bonds

The cooperation of multiple catalytic components is a powerful tool for intermolecular bond formation, specifically, cross-coupling reactions. Supported metal catalysts have interfacial sites between metal nanoparticles and their supports where multiple catalytic elements can work in cooperation to efficiently promote intermolecular reactions. Hence, the establishment of novel guidelines for designing active interfacial sites of supported metal catalysts is indispensable for heterogeneous catalysts which enable efficient cross-coupling reactions. In this article, we performed kinetic and theoretical studies to elucidate the effect of metal-support cooperation for the borylation of C-O bonds by supported gold catalysts and revealed that the Lewis acid density of the supports determined the number of active sites at which metal nanoparticles (NPs) and Lewis acid at the surface of the supports work in cooperation. Furthermore, DFT calculations revealed that strong adsorption of diborons at the interface between Au NPs and supports and a decrease in the LUMO level of adsorbed diboron were responsible for efficient C-O bond borylation. Supported Au catalysts with the optimized metal-metal oxide cooperation sites, namely, Au/α-Fe2O3 catalyst, showed excellent activity for C-O bond borylation, and also enabled the synthesis of organoboron compounds by using continuous-flow reactions. Furthermore, Au/α-Fe2O3 showed high activity for direct C-N bond borylation without the transformation of amino groups to ammonium cations. The results described herein suggest that the optimization of metal-metal oxide cooperation is beneficial for taking full advantage of the potential performance of supported metal catalysts for intermolecular reactions.

Stereocontrolled Hydrogenation of Conjugated Enones to Alcohols via Dual Iridium-Catalysis

The concept of dual catalysis is an emerging area holding high potential in terms of preparative efficiency, yet faces severe challenges in compatibility of reaction conditions and interference of catalysts. The transition-metal catalyzed stereoselective hydrogenation of olefins and ketones typically proceeds under different reaction conditions and/or uses a different reductant. As a result, these two types of hydrogenations can normally not be performed in the same pot. Herein, the stereocontrolled hydrogenation of enones to saturated alcohols is described, enabled by orthogonal dual iridium catalysis, using molecular hydrogen for both reductions. In this one-pot procedure, N,P-iridium catalysts (hydrogenation active towards olefins) and NHC,P-iridium catalysts (hydrogenation active towards ketones) operated independently of one another allowing the construction of two contiguous stereogenic centers up to 99 % ee, 99/1 d.r. Ultimately, by simple selection of the chirality of either ligands, the enone could be efficiently reduced to all four stereoisomers of the saturated alcohol in equally high stereopurity. This degree of stereocontrol for the synthesis of different stereoisomers by dual transition-metal catalyzed hydrogenation was previously not attained. The generality in substituted enones (alkyl, aryl, heteroaryl) demonstrate the wide applicability of this concept.

Divergent Reactions of α-Diazo 1,3-Dicarbonyl Compounds with Allylic Carbonates Involving Ketene versus Carbene Intermediates Enabled by Cooperative Rh(II)/Pd(0) Dual Catalysis

A cooperative Rh(II)/Pd(0) dual-catalysis strategy that enabled divergent reactions of α-diazo 1,3-dicarbonyl compounds with allylic carbonates involving ketene versus carbene intermediates is described. The efficient synthesis of α-quaternary allylated β-keto-esters was accomplished by the Rh(II)/Pd(0) dual-catalysis allylic alkylation of α-diazo 1,3-dicarbonyl compounds. Alternatively, an unprecedented (1+4) annulation of α-diazo 1,3-dicarbonyl compounds with 2-(hydroxymethyl)allyl carbonates via Rh(II)/Pd(0) dual catalysis was also successfully developed, affording a wide variety of α-quaternary tetrahydrofurans in good to high yields.

Multi-Catalytic Metal-Based Homogeneous-Heterogeneous Systems in Organic Chemistry

The combination of metal-based homogeneous and heterogeneous catalysts in the same reaction media is a powerful, yet relatively unexplored approach in organic chemistry. This strategy can address important limitations associated with purely homogeneous or heterogeneous catalysis such as the incompatibility of different catalytic species in solution, or the limited tunability of solid catalysts, respectively. Moreover, the facile reusability of the solid catalyst, contributes to increase the overall sustainability of the process. As a result, this semi-heterogeneous multi-catalytic approach has unlocked significant advances in organic chemistry, improving existing reactions and even enabling the discovery of novel transformations, exemplified by the formal alkane metathesis. This concept article aims to showcase the benefits of this strategy through the exploration of diverse relevant examples from the literature, hoping to spur research on new metal-based homogeneous-heterogeneous catalyst combinations that will result in reactivity challenging to achieve by conventional homogeneous or heterogeneous catalysis alone.

Transition metal-catalyzed C(sp2/sp3)-H α-fluoroalkenylation from gem-(bromo/di)fluoroalkenes to monofluoroalkenes: scope, mechanisms, and synthetic applications

Organofluorines have a broad range of industrial applications, such as pharmaceuticals, liquid crystal displays (LCDs), solar cells, textiles, and construction coatings, and are used in peptidomimetics, surfactants, refrigerants, anesthetics, and agrochemicals. Among them are versatile monofluoroalkenes that play a crucial role in medicinal and synthetic chemistry. The synthetic strategies for this class of molecules are limited, and prior efforts frequently suffered from poor atom- and step-economies. As a surrogate pathway for traditional cross-coupling transformations, transition metal (TM)-catalyzed C-H direct α-fluoroalkenylation overcomes these obstacles and provides straightforward techniques to access monofluoroalkenes. Nevertheless, substrate scope is still a challenge for catalysis, where gem-bromofluoroalkene synthons are applicable with electronically biased substrates such as azoles, while gem-difluoroalkene-based strategies are limited to substrates containing N-based directing groups. Herein, we review the cutting-edge fluoroalkenylation research for direct synthesis of monofluoroalkenes achieved during the last decade (2013-2023). This review is divided into two main parts: the first part discusses TM-catalyzed direct α-fluoroalkenylation via the merging of C-H activation and C(sp2)-Br cleavage strategies using gem-bromofluoroalkenes, and the second part describes the same reaction, albeit with C(sp2)-F cleavage of highly explored gem-difluoroolefins. Our review surveys all previously reported monofluoroalkenes in this research area, including their preparation techniques, stereoselectivity, and yield percentages. Furthermore, optimal conditions, reactant scope, mechanistic investigations, synthetic applications, benefits, and drawbacks of each presented methodology are critically discussed.

Switching Selectivity in Borylative Allyl-Allyl Cross-Coupling through Synergistic Catalysis

A Cu/Pd-catalyzed borylative coupling of allenes with allyl carbonates is reported. Synergistic Cu/Pd catalysis enables a divergent selectivity compared to Cu catalysis and allows for the regio-, diastereo-, and enantioselective formation of synthetically versatile chiral borylated 1,5-dienes featuring two adjacent tertiary stereocenters. DFT calculations support a closed inner-sphere SE2' transmetalation between the catalytic allyl copper and allyl palladium intermediates and point at the reductive elimination of the resulting bis(allyl)Pd intermediate as the regio- and diastereo-determining step.

Application of artificial backbone connectivity in the development of metalloenzyme mimics

Metal-dependent enzymes are abundant and vital catalytic agents in nature. The functional versatility of metalloenzymes has made them common targets for improvement by protein engineering as well as mimicry by de novo designed sequences. In both strategies, the incorporation of non-canonical cofactors and/or non-canonical side chains has proved a useful tool. Less explored-but similarly powerful-is the utilization of non-canonical covalent modifications to the polypeptide backbone itself. Such efforts can entail either introduction of limited artificial monomers in natural chains to produce heterogeneous backbones or construction of completely abiotic oligomers that adopt defined folds. Herein, we review recent research applying artificial protein-like backbones in the construction of metalloenzyme mimics, highlighting progress as well as open questions in this emerging field.

Cooperative Catalysis-Enabled (4 + 3) Cycloaddition of 2-Indolylmethanols with In Situ-Generated ortho-Naphthoquinone Methides

A cooperative catalysis-enabled (4 + 3) cycloaddition of 2-indolylmethanols with ortho-naphthoquinone methides (o-NQMs), which were in situ-generated from enynones, has been established in the presence of silver/Brønsted acid cocatalysts. In the reaction pathway, the key o-NQM intermediates were formed through Ag(I)-catalyzed cyclization of enynones, while the indole-based carbocation intermediates were generated via Brønsted acid-catalyzed dehydration of 2-indolylmethanols. By this approach, a wide range of seven-membered cyclohepta[b]indoles were synthesized in good yields with high efficiency under mild reaction conditions, which serves as a useful strategy toward constructing indole-fused seven-membered rings. Moreover, the catalytic asymmetric version of this (4 + 3) cycloaddition has been realized under the cooperative catalysis of Ag(I) with chiral phosphoric acid, which offered chiral cyclohepta[b]indole with a good enantioselectivity (75% ee). This work not only represents the first cooperative catalysis-enabled (4 + 3) cycloaddition of 2-indolylmethanols but also provides a good example for o-NQM-involved cycloadditions, which will contribute to the chemistry of 2-indolylmethanols and enrich the research contents of cooperative catalysis.

Designing core-shell heterostructure arrays based on snowflake NiCoFe-LTH shelled over W2N-WC nanowires as an advanced bi-functional electrocatalyst for boosting alkaline water/seawater electrolysis

The pursuit of efficient and sustainable hydrogen production through water splitting has led to intensive research in the field of electrocatalysis. However, the impediment posed by sluggish reaction kinetics has served as a significant barrier. This challenge has inspired the development of electrocatalysts characterized by high activity, abundance in earth's resources, and long-term stability. In addressing this obstacle, it is imperative to meticulously fine-tune the structure, morphology, and electronic state of electrocatalysts. By systematically manipulating these key parameters, the full potential of electrocatalysts can unleash, enhancing their catalytic activity and overall performance. Hence in this study, a novel heterostructure is designed, showcasing core-shell architectures achieved by covering W2N-WC nanowire arrays with tri-metallic Nickel-Cobalt-Iron layered triple hydroxide nanosheets on carbon felt support (NiCoFe-LTH/W2N-WC/CF). By integrating the different virtue such as binder free electrode design, synergistic effect between different components, core-shell structural advantages, high exposed active sites, high electrical conductivity and heterostructure design, NiCoFe-LTH/W2N-WC/CF demonstrates striking catalytic performances under alkaline conditions. The substantiation of all the mentioned advantages has been validated through electrochemical data in this study. According to these results NiCoFe-LTH/W2N-WC/CF achieves a current density of 10 mA cm-2 needs overpotential values of 101 mV for HER and 206 mV for OER, respectively. Moreover, as a bi-functional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.543 V and 1.569 V to reach a current density of 10 mA cm-2 for alkaline water and alkaline seawater electrolysis, respectively. Briefly, this research with attempting to combination of different factors try to present a promising stride towards advancing bi-functional catalytic activity with tailored architectures for practical green hydrogen production via electrochemical water splitting process.

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.

Heterogeneous Porous Synergistic Photocatalysts for Organic Transformations

Recent interest has surged in using heterogeneous carriers to boost synergistic photocatalysis for organic transformations. Heterogeneous catalysts not only facilitate synergistic enhancement of distinct catalytic centers compared to their homogeneous counterparts, but also allow for the easy recovery and reuse of catalysts. This mini-review summarizes recent advancements in developing heterogeneous carriers, including metal-organic frameworks, covalent-organic frameworks, porous organic polymers, and others, for synergistic catalytic reactions. The advantages of porous materials in heterogeneous catalysis originate from their ability to provide a high surface area, facilitate enhanced mass transport, offer a tunable chemical structure, ensure the stability of active species, and enable easy recovery and reuse of catalysts. Both photosensitizers and catalysts can be intricately incorporated into suitable porous carriers to create heterogeneous dual photocatalysts for organic transformations. Notably, experimental evidence from reported cases has shown that the catalytic efficacy of heterogeneous catalysts often surpasses that of their homogeneous analogues. This enhanced performance is attributed to the proximity and confinement effects provided by the porous nature of the carriers. It is expected that porous carriers will provide a versatile platform for integrating diverse catalysts, thus exhibiting superior performance across a range of organic transformations and appealing prospect for industrial applications.

N-Heterocyclic carbene/palladium synergistic catalysis in organic synthesis

The cooperation of two distinct catalytic cycles to activate different reactive centers leading to a chemical transformation has been classified as synergistic catalysis. The synergistic combination of NHC with palladium catalysis has emerged as a powerful strategy in the last few years. Merging the ability of NHCs to inverse the polarity of a functional group with the unique reactivity of palladium enables transformations that cannot be accomplished by either of these catalysts alone. Despite the associated challenges, such as quenching of catalysts, reactivity mismatch etc., significant development has been achieved in the field of NHC/Pd synergistic catalysis. The recent incorporation of photoredox catalysis with NHC/Pd synergistic catalysis has further advanced this area. This review highlights the developments made in the area of NHC/Pd synergistic catalysis.

Chelate Complexes of 3d Transition Metal Ions─A Challenge for Electronic-Structure Methods?

Different electronic-structure methods were assessed for their ability to predict two important properties of the industrially relevant chelating agent nitrilotriacetic acid (NTA): its selectivity with respect to six different first-row transition metal ions and the spin-state energetics of its complex with Fe(III). The investigated methods encompassed density functional theory (DFT), the random phase approximation (RPA), coupled cluster (CC) theory, and the auxiliary-field quantum Monte Carlo (AFQMC) method, as well as the complete active space self-consistent field (CASSCF) method and the respective on-top methods: second-order N-electron valence state perturbation theory (NEVPT2) and multiconfiguration pair-density functional theory (MC-PDFT). Different strategies for selecting active spaces were explored, and the density matrix renormalization group (DMRG) approach was used to solve the largest active spaces. Despite somewhat ambiguous multi-reference diagnostics, most methods gave relatively good agreement with experimental data for the chemical reactions connected to the selectivity, which only involved transition-metal complexes in their high-spin state. CC methods yielded the highest accuracy followed by range-separated DFT and AFQMC. We discussed in detail that even higher accuracies can be obtained with NEVPT2, under the prerequisite that consistent active spaces along the entire chemical reaction can be selected, which was not the case for reactions involving Fe(III). A bigger challenge for electronic-structure methods was the prediction of the spin-state energetics, which additionally involved lower spin states that exhibited larger multi-reference diagnostics. Conceptually different, typically accurate methods ranging from CC theory via DMRG-NEVPT2 in combination with large active spaces to AFQMC agreed well that the high-spin state is energetically significantly favored over the other spin states. This was in contrast to most DFT functionals and RPA which yielded a smaller stabilization and some common DFT functionals and MC-PDFT even predicting the low-spin state to be energetically most favorable.

When transition-metal catalysis meets electrosynthesis: a recent update

While aiming at sustainable synthesis, organic electrosynthesis has attracted increasing attention in the past few years. In parallel, with a deeper understanding of catalyst and ligand design, 3d transition-metal catalysis allows the conception of more straightforward synthetic routes in a cost-effective fashion. Owing to their intrinsic advantages, the merger of organic electrosynthesis with 3d transition-metal catalysis has offered huge opportunities for conceptually novel transformations while limiting ecological footprint. This review summarizes the key advancements in this direction published in the recent two years, with specific focus placed on strategy design and mechanistic aspects.

Enantioselective Tsuji-Trost α-Fluoroallylation of Amino Acid Esters with Gem-Difluorinated Cyclopropanes

A novel enantioselective Tsuji-Trost-type cross coupling reaction between gem-difluorinated cyclopropanes and N-unprotected amino acid esters enabled by synergistic Pd/Ni/chiral aldehyde catalysis is presented herein. This transformation streamlined the diversity-oriented synthesis (DOS) of optically active α-quaternary α-amino acid esters bearing a linear 2-fluoroallylic motif, which served as an appealing platform for the construction of other valuable enantioenriched compounds. The key intermediates were confirmed by HRMS detection, while DFT calculations revealed that the excellent enantioselectivity was attributed to the stabilizing non-covalent interactions between the Pd(II)-π-fluoroallyl species and the Ni(II)-Schiff base complex.

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.

Recent Advances in the Domino Annulation Reaction of Quinone Imines

Quinone imines are important derivatives of quinones with a wide range of applications in organic synthesis and the pharmaceutical industry. The attack of nucleophilic reagents on quinone imines tends to lead to aromatization of the quinone skeleton, resulting in both the high reactivity and the unique reactivity of quinone imines. The extreme value of quinone imines in the construction of nitrogen- or oxygen-containing heterocycles has attracted widespread attention, and remarkable advances have been reported recently. This review provides an overview of the application of quinone imines in the synthesis of cyclic compounds via the domino annulation reaction.

Tandem catalysis enables chlorine-containing waste as chlorination reagents

Chlorinated compounds are ubiquitous. However, accumulation of chlorine-containing waste has a negative impact on human health and the environment due to the inapplicability of common disposal methods, such as landfill and incineration. Here we report a sustainable approach to valorize chlorine-containing hydrocarbon waste, including solids (chlorinated polymers) and liquids (chlorinated solvents), based on copper and palladium catalysts with a NaNO3 promoter. In the process, waste is oxidized to release the chlorine in the presence of N-directing arenes to afford valuable aryl chlorides, such as the FDA-approved drug vismodegib. The remaining hydrocarbon component is mineralized to afford CO, CO2 and H2O. Moreover, the CO and CO2 generated could be further utilized directly. Thus, chlorine-containing hydrocarbon waste, including mixed waste, can serve as chlorination reagents that neither generate hazardous by-products nor involve specialty chlorination reagents. This tandem catalytic approach represents a promising method for the viable management of a wide and diverse range of chlorine-containing hydrocarbon wastes.

Diastereo-divergent synthesis of chiral hindered ethers via a synergistic calcium(II)/gold(I) catalyzed cascade hydration/1,4-addition reaction

Hindered ethers are ubiquitous in natural products and bioactive molecules. However, developing an efficient method for the stereocontrolled synthesis of all stereoisomers of chiral hindered ethers is highly desirable but challenging. Here we show a strategy that utilizes in situ-generated water as a nucleophile in an asymmetric cascade reaction involving two highly reactive intermediates, 3-furyl methyl cations and ortho-quinone methides (o-QMs), to synthesize chiral hindered ethers. The Ca(II)/Au(I) synergistic catalytic system enables the control of diastereoselectivity and enantioselectivity by selecting suitable chiral phosphine ligands in this cascade hydration/1,4-addition reaction, affording all four stereoisomers of a diverse range of chiral tetra-aryl substituted ethers with high diastereoselectivities (up to >20/1) and enantioselectivities (up to 95% ee). This work provides an example of chiral Ca(II)/Au(I) bimetallic catalytic system controlling two stereogenic centers via a cascade reaction in a single operation.

Synthesis of a Triangle-Fused Six-Pointed Star and Its Electrocatalytic CO2 Reduction Activity

As electrocatalysts, molecular catalysts with large aromatic systems (such as terpyridine, porphyrin, or phthalocyanine) have been widely applied in the CO2 reduction reaction (CO2RR). However, these monomeric catalysts tend to aggregate due to strong π-π interactions, resulting in limited accessibility of the active site. In light of these challenges, we present a novel strategy of active site isolation for enhancing the CO2RR. Six Ru(Tpy)2 were integrated into the skeleton of a metallo-organic supramolecule by stepwise self-assembly in order to form a rhombus-fused six-pointed star R1 with active site isolation. The turnover frequency (TOF) of R1 was as high as 10.73 s-1 at -0.6 V versus reversible hydrogen electrode (vs RHE), which is the best reported value so far at the same potential to our knowledge. Furthermore, by increasing the connector density on R1's skeleton, a more stable triangle-fused six-pointed star T1 was successfully synthesized. T1 exhibits exceptional stability up to 126 h at -0.4 V vs RHE and excellent TOF values of CO. The strategy of active site isolation and connector density increment significantly enhanced the catalytic activity by increasing the exposure of the active site. This work provides a starting point for the design of molecular catalysts and facilitates the development of a new generation of catalysts with a high catalytic performance.

Ultrafast Halogen Dance Reactions of Bromoarenes Enabled by Catalytic Potassium Hexamethyldisilazide

Lochmann-Schlosser base, a stoichiometric combination of nBuLi and KOtBu, is commonly used as a superbase for deprotonating a wide range of organic compounds. In the present study, we report that catalytic potassium hexamethyldisilazide (KHMDS) exhibits higher catalytic activity than KOtBu for successive bromine-metal exchanges. Accordingly, 1-10 mol% of KHMDS dramatically enhances halogen dance reactions to introduce various electrophiles to bromopyridine, bromoimidazole, bromothiophene, bromofuran, and bromobenzene derivatives with the bromo group translocated from the original position. A dual catalytic cycle is proposed to explain the ultrafast bromine transfer.

Deep degradation of atrazine in water using co-immobilized laccase-1-hydroxybenzotriazole-Pd as composite biocatalyst

The efficient and green removal technology of refractory organics such as atrazine in water has been an important topic of research in water treatment. A novel membrane composite biocatalyst Lac-HBT-Pd/BC as prepared for the first time by co-immobilizing laccase, mediator 1-hydroxybenzotriazole (HBT) and metal Pd on functionalized bacterial cellulose (BC) to investigate the removal of atrazine and degradation of its intermediates under mild ambient conditions. It was found that atrazine could be completely degraded in 5 h by the catalysis of Lac-HBT-Pd/BC, and the removal rate of degradation intermediates from atrazine was about 85% after continuous catalysis, which achieved deep degradation of atrazine. The effect of electrochemical activity and radical stability of the membrane composite biocatalysts loaded with Pd was investigated. The possible degradation pathways were proposed by identifying and analyzing the deep degradation products of atrazine. The Lac-HBT-Pd/BC demonstrated deep degradation of atrazine and favorable reusability as well as considerable adaptability to various water qualities. This work provides an important reference for preparing new kinds of biocatalysts to degrade refractory organic pollutants in water.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

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.

Diagnosis of Mycobacterium tuberculosis using palladium-platinum bimetallic nanoparticles combined with paper-based analytical devices

In this study, we demonstrate that palladium-platinum bimetallic nanoparticles (Pd@Pt NPs) as the nanozyme, combined with a multi-layer paper-based analytical device and DNA hybridization, can successfully detect Mycobacterium tuberculosis. This nanozyme has peroxidase-like properties, which can increase the oxidation rate of the substrate. Compared with horseradish peroxidase, which is widely used in traditional detection, the Michaelis constants of Pd@Pt NPs are fourteen and seventeen times lower than those for 3,3',5,5'-tetramethylbenzidine and H2O2, respectively. To verify the catalytic efficiency of Pd@Pt NPs, this study will execute molecular diagnosis of Mycobacterium tuberculosis. We chose the IS6110 fragment as the target DNA and divided the complementary sequences into the capture DNA and reporter DNA. They were modified on paper and Pd@Pt NPs, respectively, to detect Mycobacterium tuberculosis on a paper-based analytical device. With the above-mentioned method, we can detect target DNA within 15 minutes with a linear range between 0.75 and 10 nM, and a detection limit of 0.216 nM. These results demonstrate that the proposed platform (a DNA-nanozyme integrated paper-based analytical device, dnPAD) can provide sensitive and on-site infection prognosis in areas with insufficient medical resources.

Construction of indolizine scaffolds from α,ω-alkynoic acids and α,ω-vinylamines via sequential-relay catalysis in "one pot"

A simple and efficient method has been developed for the synthesis of a diverse range of aryl-fused indolizin-3-ones through sequential Au(I)-catalyzed hydrocarboxylation, aminolysis, and cyclization, followed by ruthenium-catalyzed ring-closing metathesis. Moderate to good yields were observed with satisfactory substrate scope and functional group tolerance. The developed protocol represents a practical strategy for the construction of bioactive aryl-fused indolizin-3-ones.

Double pyramid stacked CoO nano-crystals induced by graphene at low temperatures as highly efficient Fenton-like catalysts

Transition metal oxides are widely used as Fenton-like catalysts in the treatment of organic pollutants, but their synthesis usually requires a high temperature. Herein, an all-solid-state synthesis method controlled by graphene was used to prepare a double pyramid stacked CoO nano-crystal at a low temperature. The preparation temperature decreased by 200 °C (over 30% reduction) due to the introduction of graphene, largely reducing the reaction energy barrier. Interestingly, the corresponding degradation rate constants (kobs) of this graphene-supported pyramid CoO nano-crystals for organic molecules after their adsorption were over 2.5 and 35 times higher than that before adsorption and that of free CoO, respectively. This high catalytic efficiency is attributed to the adsorption of pollutants at the surface by supporting graphene layers, while free radicals activated by CoO can directly and rapidly contact and degrade them. These findings provide a new strategy to prepare low carbon-consuming transition metal oxides for highly efficient Fenton-like catalysts.

Enantioselective merged gold/organocatalysis

Gold complexes, because of their unique carbophilic nature, have evolved as efficient catalysts for catalyzing various functionalization reactions of C-C multiple bonds. However, the realization of enantioselective transformations via gold catalysis remains challenging due to the geometrical constraints and coordination behaviors of gold complexes. In this context, merged gold/organocatalysis has emerged as one of the intriguing strategies to achieve enantioselective transformations which could not be possible by using a single catalytic system. Historically, in 2009, this field started with the merging of gold with axially chiral Brønsted acids and chiral amines to achieve enantioselective transformations. Since then, based on the unique reactivity profiles offered by each catalyst, several reports utilizing gold in conjunction with various chiral organocatalysts such as amines, Brønsted acids, N-heterocyclic carbenes, hydrogen-bonding and phosphine catalysts have been documented in the literature. This article demonstrates an up-to-date development in this field, especially focusing on the mechanistic interplay of gold catalysts with chiral organocatalysts.

Z-Retentive Asymmetric Allylic Substitution Reactions of Aldimine Esters under Ru/Cu Dual Catalysis

Ru/Cu dual catalysis has been applied for Z-retentive asymmetric allylic substitution reactions of aldimine esters. This reaction provides an enantioselective synthesis of chiral Z-olefins in high yields (up to 91% yield) with excellent enantioselectivity (up to 98% ee) under mild conditions. The previously unreacted trisubstituted allylic electrophiles under Ir catalytic system are found to be compatible, affording the stereoretentive products in either Z- or E-form. Both linear and branched allylic electrophiles are suitable substrates with excellent reaction outcomes. Notably, Ru and Cu complexes are added in one-pot and simplifies the manipulation of this protocol and self-sorting phenomena could be observed in this Ru/Cu dual catalytic system.

Divergent Geminal Alkynylation-Allylation and Acylation-Allylation of Carbenes: Evolution and Roles of Two Transition-Metal Catalysts

Cooperative bimetallic catalysis to access novel reactivities is a powerful strategy for reaction development in transition-metal-catalyzed chemistry. Particularly, elucidation of the evolution of two transition-metal catalysts and understanding their roles in dual catalysis are among the most fundamental goals for bimetallic catalysis. Herein, a novel three-component reaction of a terminal alkyne, a diazo ester, and an allylic carbonate was successfully developed via cooperative Cu/Rh catalysis with Xantphos as the ligand, providing a highly efficient strategy to access 1,5-enynes with an all-carbon quaternary center that can be used as immediate synthetic precursors for complex cyclic molecules. Notably, a Meyer-Schuster rearrangement was involved in the reactions using propargylic alcohols, resulting in an unprecedented acylation-allylation of carbenes. Mechanistic studies suggested that in the course of the reaction Cu(I) species might aggregate to some types of Cu clusters and nanoparticles (NPs), while the Rh(II)2 precursor can dissociate to mono-Rh species, wherein Cu NPs are proposed to be responsible for the alkynylation of carbenes and work in cooperation with Xantphos-coordinated dirhodium(II) or Rh(I)-catalyzed allylic alkylation.

Cooperative Cu/Pd-Catalyzed 1,5-Boroacylation of Cyclopropyl-Substituted Alkylidenecyclopropanes

A Cu/Pd-cocatalyzed 1,5-boroacylation of cyclopropyl-substituted ACPs with B2pin2 and acid chlorides has been developed. Using cyclopropyl-substituted ACPs as the starting material, a broad range of 1,5-boroacylated products with multiple functional groups was prepared in good yields with excellent regio- and stereoselectively. Both aromatic and aliphatic acid chlorides were tolerated in this reaction.

Framework confinement of multi-metals within silica hollow spheres by one-pot synthesis process

The control incorporation of metals in silica hollow spheres (SHSs) may bring new functions to silica mesoporous structures for applications including catalysis, sensing, molecular delivery, adsorption filtration, and storage. However, the strategies for incorporating metals, whether through pre-loading in the hollow interior or post-encapsulation in the mesoporous shell, still face challenges in achieving quantitative doping of various metals and preventing metal aggregation or channel blockage during usage. In this study, we explored the doping of different metals into silica hollow spheres based on the dissolution-regrowth process of silica. The process may promote the formation of more structural defects and functional silanol groups, which could facilitate the fixation of metals in the silica networks. With this simple and efficient approach, we successfully achieved the integration of ten diverse metal species into silica hollow sphere (SHS). Various single-metal, dual-metal, triple-metal, and quadruple-metal doped SHSs have been prepared, with the doped metals being stable and homogeneously dispersed in the structure. Based on the structural characterizations, we analyzed the influence of metal types on the morphology features of SHSs. The synergistic effects of multi-metals on the catalysis applications were also studied and compared.

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.

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.

Theoretical study of the saturation and nature of the hydrogen bonds to gold

Traditional hydrogen bonds are well-known to exhibit directionality and saturation. By contrast, gold involved hydrogen bonds (GHBs) have been extensively studied but remain lack of in-depth understanding towards the intrinsic nature and saturation property. This work exemplifies three series of complexes: [L-Au-L]-⋯(HF)n (L = H, CH3, (CH3)3; n = 1-8) containing GHBs to dig into the intrinsic nature with the aid of multiple theoretical analysis methods, finding that the formation of GHB is highly subject to orbital interactions along with steric hindrance. Moreover, the saturation level of GHBs largely depends on the ligand attached to the gold center, since different ligands typically possess varying electron-giving ability and steric volume. This work confirms the coexistence of as many as 6 GHBs for one Au atom and thoroughly studies the saturation level of GHBs, which will provide new insights into GHBs and facilitate future synthesis of more complicated gold complexes.