Different Strategies for Designing Dual-Catalytic Enantioselective Processes: From Fully Cooperative to Non-cooperative Systems

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.

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

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

A Merger of Relay Catalysis with Dynamic Kinetic Resolution Enables Enantioselective β-C(sp3)-H Arylation of Alcohols

The conceptual merger of relay catalysis with dynamic kinetic resolution strategy is reported to enable regio- and enantioselective C(sp3)-H bond arylation of aliphatic alcohols, forming enantioenriched β-aryl alcohols typically with >90 : 10 enantiomeric ratios (up to 98 : 2 er) and 36-74 % yields. The starting materials bearing neighbouring stereogenic centres can be converted to either diastereomer of the β-aryl alcohol products, with >85 : 15 diastereomeric ratios determined by the catalysts. The reactions occur under mild conditions, ensuring broad compatibility, and involve readily available aryl bromides, an inorganic base, and commercial Ru- and Pd-complexes. Mechanistic experiments support the envisioned mechanism of the transformation occurring through a network of regio- and stereoselective processes operated by a coherent Ru/Pd-dual catalytic system.

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.

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

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

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.

Enantioselective Cross-[4 + 2]-Cycloaddition/Decarboxylation of 2-Pyrones by Cooperative Catalysis of the Pd(0)/NHC Complex and Chiral Phosphoric Acid

Here, we describe a cooperative Pd(0)/chiral phosphoric acid catalytic system that allows us to realize the first chemo-, regio-, and enantioselective sequential cross-[4 + 2]-cycloaddition/decarboxylation reaction between 2-pyrones and unactivated acyclic 1,3-dienes. The key to the success of this transformation is the utilization of an achiral N-heterocyclic carbene (NHC) as the ligand and a newly developed chiral phosphoric acid as the cocatalyst. Experimental investigations and computational studies support the idea that the Pd(0)/NHC complex acts as a π-Lewis base to increase the nucleophilicity of 1,3-dienes via η2 coordination, while the chiral phosphoric acid simultaneously increases the electrophilicity of 2-pyrones by hydrogen bonding. By this synergistic catalysis, the sequential cross-[4 + 2]-cycloaddition and decarboxylation reaction proceeds efficiently, enabling the preparation of a wide range of chiral vinyl-substituted 1,3-cyclohexadienes in good yields and enantioselectivities. The synthetic utility of this reaction is demonstrated by synthetic transformations of the product to various valuable chiral six-membered carbocycles.

Asymmetric α-C(sp3)-H allylic alkylation of primary alkylamines by synergistic Ir/ketone catalysis

Primary alkyl amines are highly reactive in N-nucleophilic reactions with electrophiles. However, their α-C-H bonds are unreactive towards electrophiles due to their extremely low acidity (pKa ~57). Nonetheless, 1,8-diazafluoren-9-one (DFO) can activate primary alkyl amines by increasing the acidity of the α-amino C-H bonds by up to 1044 times. This makes the α-amino C-H bonds acidic enough to be deprotonated under mild conditions. By combining DFO with an iridium catalyst, direct asymmetric α-C-H alkylation of NH2-unprotected primary alkyl amines with allylic carbonates has been achieved. This reaction produces a wide range of chiral homoallylic amines with high enantiopurities. The approach has successfully switched the reactivity between primary alkyl amines and allylic carbonates from intrinsic allylic amination to the α-C-H alkylation, enabling the construction of pharmaceutically significant chiral homoallylic amines from readily available primary alkyl amines in a single step.

Bridging the incompatibility gap in dual asymmetric catalysis over a thermoresponsive hydrogel-supported catalyst

The integration of dual asymmetric catalysis is highly beneficial for the synthesis of organic molecules with multiple stereocenters. However, two major issues that need to be addressed are the intrinsic deactivation of dual-species and the extrinsic conflict of reaction conditions. To overcome these concerns, we have utilized the compartmental and thermoresponsive properties of poly(N-isopropylacrylamide) (PNIPAM) to develop a cross-linked PNIPAM-hydrogel-supported bifunctional catalyst. This catalyst is designed with Rh(diene) species situated on the outer surface and Ru(diamine) species positioned within the interior of the hydrogel. The compartmental function of PNIPAM in the middle overcomes intrinsic mutual deactivations between the dual-species. The thermoresponsive nature of PNIPAM allows for precise control of catalytic pathways in resolving external conflicts by controlling the reaction switching between an Rh-catalyzed enantioselective 1,4-addition at 50°C and a Ru-catalyzed asymmetric transfer hydrogenation (ATH) at 25°C. As we envisioned, this sequential 1,4-addition/reduction dual enantioselective cascade reaction achieves a transformation from incompatibility to compatibility, resulting in direct access to γ-substituted cyclic alcohols with dual stereocenters in high yields and enantio/diastereoselectivities. Mechanistic investigation reveals a reversible temperature transition between 50°C and 25°C, ensuring a cascade process comprising a 1,4-addition followed by the ATH process.

Enamine/Iminium-based Dual Organocatalytic Systems for Asymmetric Catalysis and Synthesis

The rational combination of two catalysts to expedite the construction of chiral complex biologically and pharmacologically relevant chiral compounds has widely gained momentum over the past decade. In particular, enamine or iminium catalysis ensuing from the activation of aldehyde or ketone by chiral amine catalysts in conjugation with other organocatalytic cycles has facilitated several asymmetric transformations to yield the enantioenriched products. Regardless of the considerable discussion on the various dual catalytic approaches, literature lacks a comprehensive review focusing on the enamine and iminium-based dual organocatalytic systems. Thus, this review article has discussed the noteworthy achievements in the field of asymmetric catalysis and synthesis catalyzed by the enamine and iminium-based dual organocatalytic systems.

Variable structure diversification by multicatalysis: the case of alcohols

Given that alcohol moieties are present in a great diversity of valuable fine chemicals from nature and synthesis, methods enabling their structure diversification are highly sought after. Catalysis proved to enable the development of new transformations that are beyond the inherent reactivity of alcohols. However, modifying the structure of alcohols at certain unbiased positions remains a major challenge or requires tedious multistep procedures. Recently, increased attention has been given to multicatalyis, which combines multiple reactions and catalysts within one system, creating room for discovering previously inaccessible reactivities or increasing the overall efficiency of multistep transformations. This feature article focuses on demonstrating various aspects of devising such multicatalytic systems that modify the structure of alcohol-containing compounds. Special attention is given to highlighting the challenges and advantages of multicatalysis, and in a broader context discussing how the field of catalysis may progress toward more complex systems.

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.

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.

Mechanism of a Dually Catalyzed Enantioselective Oxa-Pictet-Spengler Reaction and the Development of a Stereodivergent Variant

Enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes proceed under weakly acidic conditions utilizing a combination of two catalysts, an indoline HCl salt and a bisthiourea compound. Mechanistic investigations revealed the roles of both catalysts and confirmed the involvement of oxocarbenium ion intermediates, ruling out alternative scenarios. A stereochemical model was derived from density functional theory calculations, which provided the basis for the development of a highly enantioselective stereodivergent variant with racemic tryptophol derivatives.

Sustainable and practical formation of carbon-carbon and carbon-heteroatom bonds employing organo-alkali metal reagents

Metal-catalysed cross-coupling reactions are amongst the most widely used methods to directly construct new bonds. In this connection, sustainable and practical protocols, especially transition metal-catalysed cross-coupling reactions, have become the focus in many aspects of synthetic chemistry due to their high efficiency and atom economy. This review summarises recent advances from 2012 to 2022 in the formation of carbon-carbon bonds and carbon-heteroatom bonds by employing organo-alkali metal reagents.

An enantioselective four-component reaction via assembling two reaction intermediates

A reaction intermediate is a key molecular entity that has been used in explaining how starting materials converts into the final products in the reaction, and it is usually unstable, highly reactive, and short-lived. Extensive efforts have been devoted in identifying and characterizing such species via advanced physico-chemical analytical techniques. As an appealing alternative, trapping experiments are powerful tools in this field. This trapping strategy opens an opportunity to discover multicomponent reactions. In this work, we report various highly diastereoselective and enantioselective four-component reactions (containing alcohols, diazoesters, enamines/indoles and aldehydes) which involve the coupling of in situ generated intermediates (iminium and enol). The reaction conditions presented herein to produce over 100 examples of four-component reaction products proceed under mild reaction conditions and show high functional group tolerance to a broad range of substrates. Based on experimental and computational analyses, a plausible mechanism of this multicomponent reaction is proposed.

Enantioselective and Diastereodivergent Allylation of Propargylic C-H Bonds

An iridium-catalyzed stereoselective coupling of allylic ethers and alkynes to generate 3,4-substituted 1,5-enynes is reported. Under optimized conditions, the coupling products are formed with excellent regio-, diastereo-, and enantioselectivities, and the protocol is functional group tolerant. Moreover, we report conditions that allow the reaction to proceed with complete reversal of diastereoselectivity. Mechanistic studies are consistent with an unprecedented dual role for the iridium catalyst, enabling the propargylic deprotonation of the alkyne through π-coordination, as well as the generation of a π-allyl species from the allylic ether starting material.

Preparation of Functionalized Amides Using Dicarbamoylzincs

We report a new convenient preparation of dicarbamoylzincs of type (R1 R2 NCO)2 Zn by the treatment of ZnCl2 and formamides R1 R2 NCHO with LiTMP in THF (15 °C, 15 min) or by the reaction of formamides R1 R2 NCHO with TMP2 Zn (25 °C, 16 h). This second method tolerates sensitive groups such as an ester, ketone or nitro function. Reaction of these dicarbamoylzincs with allylic, benzylic, aryl, alkenyl bromides, acid chlorides, aldehydes or enones provided various polyfunctional amides in 47-97 % yields. 13 C NMR characterization of these new carbamoylzinc derivatives is reported.

Recent Applications on Dual-Catalysis for C–C and C–X Cross-Coupling Reactions

Coupling reactions stand amid the most significant reactions in synthetic organic chemistry. Of late, these coupling strategies are being viewed as a versatile synthetic tool for a wide range of organic transformations in many sectors of chemistry, ranging from indispensable synthetic scaffolds and natural products of biological significance to novel organic materials. Further, the use of dual-catalysis in accomplishing various interesting cross-coupling transformations is an emerging field in synthetic organic chemistry, owing to their high catalytic performance rather than the use of a single catalyst. In recent years, synthetic organic chemists have given considerable attention to hetero-dual catalysis; wherein these catalytic systems have been employed for the construction of versatile carbon–carbon [C(sp 3)–C(sp 3), C(sp 3)–C(sp 2), C(sp 2)–C(sp 2)] and carbon–heteroatom (C–N, C–O, C–P, C–S) bonds. Therefore, in this mini-review, we are emphasizing recently developed various cross-coupling reactions catalysed by transition-metal dual-catalysis (i.e., using palladium and copper catalysts, but omitting the reports on photoredox/metal catalysis).

1 Introduction

2 Cu/Pd-Catalysed Bond Formation

2.1 Pd/Cu-Catalysed C(sp 3)–C(sp 2) Bond Formation

2.2 Pd/Cu-Catalysed C(sp 2)–C(sp 2) Bond Formation

2.3 Pd/Cu-Catalysed C(sp)–C(sp 2) Bond Formation

2.4 Pd/Cu-Catalysed C(sp 3)–C(sp 3) Bond Formation

2.5 Pd/Cu-Catalysed C–X (X = B, N, P, S, Si) Bond Formation

3 Conclusion

Recent progress in asymmetric synergistic catalysis - the judicious combination of selected chiral aminocatalysts with achiral metal catalysts

In this review we survey recent synergistic applications of a chiral organocatalyst with an achiral metal to perform stereoselective transformations of synthetic utility (since 2016). The transformations are classified by the modes of reactivity deployed, focussing on organocatalytic activation of carbonyl substrates as chiral nucleophiles via the α-position (e.g., as enamines) and as chiral electrophiles via the β-position (e.g., as iminium ions) combined with complementary activation of their reaction partners by an achiral metal co-catalyst (e.g., Pd or Cu-based). Corresponding radical reactions are also presented in which photocatalysis mediated by achiral metal complexes replaces the metal co-catalyst. Certain privileged structures are revealed and opportunities to develop this exciting field are highlighted.

A critical survey of recent synergistic applications of a chiral organocatalyst with an achiral metal to perform stereoselective transformations of synthetic utility.

Enantioselective Organocopper-Catalyzed Hetero Diels-Alder Reaction through in Situ Oxidation of Ethers into Enol Ethers

We disclose a catalytic method for the enantio- and diastereoselective union of alkyl ethers and heterodienes. We demonstrate that a chiral Cu-BOX complex catalyzes the efficient oxidation of ethers into enol ethers in the presence of trityl acetate. Then, the organocopper promotes stereoselective hetero Diels-Alder reaction between the in situ generated enol ethers and β,γ-unsaturated ketoesters, allowing for rapid access to an array of dihydropyran derivatives possessing three vicinal stereogenic centers.

Stereodivergent propargylic alkylation of enals via cooperative NHC and copper catalysis

Despite that asymmetric stereodivergent synthesis has experienced great success to provide unusual processes for the creation of chirality complexity, concepts appliable to asymmetric stereodivergent catalysis are still limited. The dependence on the unusual capacity of each catalyst to precisely control the reactive site planar in the region poses unparalleled constraints on this field. Here, we first demonstrate that the chiral Cu-allenylidene species can participate in the stereodivergent propargylic alkylation of enals, in concert with chiral N-heterocyclic carbenes (NHCs). Thus, all four stereoisomers were obtained with excellent enantioselectivity and diastereoselectivity (up to >99% e.e. and >95:5 d.r.) from the same starting materials by simply altering chiral Cu-Pybox complex and NHC combinations. The rich chemistry workable in the products enables the structurally diverse synthesis of chiral functional molecules and holds great potential in alkaloid synthesis, as showcased by the preparation of the key building block to access (-)-perophoramidine.

The ability to construct multiple stereocenters in a modular fashion is an important goal of synthetic organic chemistry. Here the authors present a method to construct oxindoles in four stereoisomers with high enantioselectivity and diastereoselectivity from the same starting materials by using cooperative copper- and organocatalysis.

Cooperative Pd/Cu Catalysis for Alkene Arylboration: Opportunities for Divergent Reactivity

A preeminent challenge in alkene difunctionalization is the control of regio-, diastereo-, and enantioselectivity. In this Perspective, a Pd/Cu-cooperative catalytic system for alkene arylboration is highlighted that allows for the controlled introduction of substituents. In particular, examples that allowed for divergent reactivity from a single substrate based on the tuning of catalysts and reaction conditions are emphasized.

Asymmetric synthesis of dihydrocarbazoles through a Friedel-Crafts alkylation/annulation sequential reaction of indoles

An enantioselective tandem Friedel-Crafts alkylation/annulation of indoles with diazoacetoacetate enones is realized in one pot. A series of dihydrocarbazoles were obtained in moderate yields with good to excellent ee values by using a Rh^II/Sc^III dual-metallic catalyst system. Control experiments revealed that Sc^III is critical to both the alkylation and annulation.

Construction of Enantioenriched γ,γ-Disubstituted Butenolides Enabled by Chiral Amine and Lewis Acid Cascade Cocatalysis

Herein we report a cascade cocatalysis strategy for the facile construction of chiral γ,γ-disubstituted butenolides. The synthetic manifold employs simple alkynoic acids instead of the preformed silyloxy furans or 5-substituted furan-2(3H)-ones. In situ formed 5-substituted furan-2(3H)-ones by AgNO₃ or Ph₃PAuCl/AgOTf catalyzed cyclization of alkynoic acids can smoothly engage in the subsequent chiral diphenylprolinol TMS-ether catalyzed Michael and Michael-aldol reactions. The cascade process serves as a general approach to chiral quaternary γ,γ-disubstituted butenolides.

Copper(i)-catalyzed asymmetric intramolecular C-arylation with ureas as the additives: highly enantioselective formation of spirooxindoles

A cooperative catalytic strategy is developed for a copper-catalyzed asymmetric intramolecular C-arylation reaction with ureas as the co-catalysts. By forming hydrogen bonds with 1,3-dicarbonyl structures, ureas can activate the substrates, stabilize the carbanion intermediates and the products, and fix the syn-configurations of 1,3-dicarbonyl structures. They help enhance the reactivity, prevent side reactions and improve the enantioselectivities.

A Diastereodivergent and Enantioselective Approach to syn- and anti-Diamines: Development of 2-Azatrienes for Cu-Catalyzed Reductive Couplings with Imines That Furnish Allylic Amines

We introduce a new reagent class, 2-azatrienes, as a platform for catalytic enantioselective synthesis of allylic amines. Herein, we demonstrate their promise by a diastereodivergent synthesis of syn- and anti-1,2-diamines through their Cu-bis(phosphine)-catalyzed reductive couplings with imines. With Ph-BPE as the supporting ligand, anti-diamines are obtained (up to 91% yield, >20:1 dr, and >99:1 er), and with the rarely utilized t-Bu-BDPP, syn-diamines are generated (up to 76% yield, 1:>20 dr, and 97:3 er).

Tandem Catalytic Indolization/Enantioconvergent Substitution of Alcohols by Borrowing Hydrogen to Access Tricyclic Indoles

An efficient tandem catalysis method is achieved for the direct conversion of alcohol-containing alkynyl anilines to valuable chiral 2,3-fused tricyclic indoles. This method relies on a tandem indolization followed by enantioconvergent substitution of alcohols via borrowing hydrogen to construct two rings in one step, enabled by relay and cooperative catalysis of a chiral iridium complex with a chiral phosphoric acid. Highly diastereoselective transformations of the tricyclic indole products also provide efficient access to a diverse array of complex polycyclic indoline compounds.

Enantio- and Diastereodivergent Sequential Catalysis Featuring Two Transition-Metal-Catalyzed Asymmetric Reactions

This study demonstrates the feasibility and inherent benefits of combining two distinct asymmetric transition-metal-catalyzed reactions in one pot. The reported transformation features a Pd-catalyzed asymmetric allylic alkylation and a Rh-catalyzed enantioselective 1,4-conjugate addition, effectively converting simple allyl enol carbonate precursors into enantioenriched cyclic ketones with two remote stereocenters. Despite the anticipated challenges associated with controlling stereoselectivity in such a complex system, the products are obtained in enantiomeric excesses ranging up to >99 % ee, exceeding those obtained from either of the individual asymmetric reactions. In addition, since the stereoselectivity of both steps is under catalyst control, this one-pot reaction is enantio- and diastereodivergent, enabling facile access to all stereoisomers from the same set of starting materials.

Enantioselective α-Arylation of Primary Alcohols under Sequential One-Pot Catalysis

Secondary benzylic alcohols and diarylmethanols are common structural motifs of biologically active and medicinally relevant compounds. Here we report their enantioselective synthesis by α-arylation of primary aliphatic and benzylic alcohols under sequential catalysis integrating a Ru-catalyzed hydrogen transfer oxidation and a Ru-catalyzed nucleophilic addition. The method can be applied to various alcohols and aryl nucleophiles tolerating a range of functional groups, including secondary alcohols, ketones, alkenes, esters, NH amides, tertiary amines, aryl halides, and heterocycles.

Stereodivergent Synthesis of Enantioenriched 2,3-Disubstituted Dihydrobenzofurans via a One-Pot C-H Functionalization/Oxa-Michael Addition Cascade

A one-pot rhodium-catalyzed C-H functionalization/organocatalyzed oxa-Michael addition cascade reaction has been developed. This methodology enables the stereodivergent synthesis of diverse 2,3-disubstituted dihydrobenzofurans with broad functional group compatibility in good yields with high levels of stereoselectivity under exceptionally mild conditions. The full complement of stereoisomers of chiral 2,3-disubstituted dihydrobenzofurans and 3,4-disubstituted isochromans could be accessed at will by appropriate permutations of the two chiral catalysts. The current work provides a rare example of two chiral catalysts independently controlling two contiguous stereogenic centers subsequently via a two-step reaction in a single operation.

Synergistic Dual Catalytic System and Kinetics for the Alcoholysis of Poly(Lactic Acid)

Plastic pollution is a global issue that is approaching crisis levels as plastic production is projected to reach 1.1 GT annually by 2050. The bioplastic industry along with a circular production economy are solutions to this problem. One promising bioplastic polylactic acid (PLA) has mechanical properties comparable to polystyrene (PS), so it could replace PS in its applications as a more environmentally sustainable material. However, since the bioplastic PLA also suffers from long biodegradation times in the environment, to ensure that it does not add to the current pollution problem, it should instead be chemically recycled. In this work, PLA was chemically recycled via alcoholysis, using either methanol or ethanol to generate the value-added products methyl lactate and ethyl lactate respectively. Two catalysts, zinc acetate dihydrate (ZnAc) and 4-(dimethylamino)pyridine (DMAP), were tested both individually and in mixtures. A synergistic effect was exhibited on the reaction rate when both catalysts were used in an equal ratio. The methanolysis reaction was determined to be two-step, with the activation energy estimated to be 73 kJ mol−1 for the first step and 40.16 kJ mol−1 for the second step. Both catalysts are cheap and commercially available, their synergistic effect could be exploited for large-scale PLA recycling.

Copper Catalyzed Decarboxylative Functionalization of Ketoacids

Selective copper catalyzed activation of ketoacids and notably bio-sourced 1,3-acetonedicarboxylic acid, represents an attractive strategy to solve key synthetic challenges. Condensation with aldehydes under exceedingly mild conditions can create more rapidly known natural products scaffolds such as 1,3 polyols. In this account, the recent progress in this field, notably through multicatalytic combination with organocatalysis is described. In addition to the rapid preparation of natural product fragments, cascade incorporation of fluorine also provided new type of synthetic analogues of improved properties in a broad range of applications.

Reductive Arylation of Amides via a Nickel-Catalyzed Suzuki-Miyaura-Coupling and Transfer-Hydrogenation Cascade

We report a means to achieve the addition of two disparate nucleophiles to the amide carbonyl carbon in a single operational step. Our method takes advantage of non-precious-metal catalysis and allows for the facile conversion of amides to chiral alcohols via a one-pot Suzuki-Miyaura cross-coupling/transfer-hydrogenation process. This study is anticipated to promote the development of new transformations that allow for the conversion of carboxylic acid derivatives to functional groups bearing stereogenic centers via cascade processes.

Enantioselective Synthesis of N-Alkylamines through β-Amino C-H Functionalization Promoted by Cooperative Actions of B(C6F5)3 and a Chiral Lewis Acid Co-Catalyst

We disclose a catalytic method for β-C(sp³)-H functionalization of N-alkylamines for the synthesis of enantiomerically enriched β-substituted amines, entities prevalent in pharmaceutical compounds and used to generate different families of chiral catalysts. We demonstrate that a catalyst system comprising of seemingly competitive Lewis acids, B(C₆F₅)₃, and a chiral Mg- or Sc-based complex, promotes the highly enantioselective union of N-alkylamines and α,β-unsaturated compounds. An array of δ-amino carbonyl compounds was synthesized under redox-neutral conditions by enantioselective reaction of a N-alkylamine-derived enamine and an electrophile activated by the chiral Lewis acid co-catalyst. The utility of the approach is highlighted by late-stage β-C-H functionalization of bioactive amines. Investigations in regard to the mechanistic nuances of the catalytic processes are described.

Umpolung coupling of pyridine-2-carboxaldehydes and propargylic carbonates via N-heterocyclic carbene/palladium synergetic catalysis

The umpolung cross-coupling reaction of pyridine-2-carboxaldehydes and propargylic carbonates has been developed for the first time through N-heterocyclic carbene/palladium cooperative catalysis with the judicious selection of the palladium catalyst, ligand and N-heterocyclic carbene, giving the propargylic ketones regioselectively.