Dual Catalysis Research Articles

Dual Catalysis Involving Organoboron Compounds

AbstractIn recent years, organoboron compounds has attracted much attention due to their unique chemical properties. In this Review, we summarize catalytic reactions via the dual catalysis of boron and another catalyst, which showed specific catalytic activity in organic transformations.

Pd/Rh Dual Catalysis: Tandem Isomerization–Allylation to Access α-Quaternary Carbonyl Compounds

A dual metal approach enables the use of unsymmetrical diallyl carbonates as viable enolate precursors for allylic alkylation reactions, allowing facile access to various α-quaternary allylated aldehydes and ketones. This methodology features a regioselective Pd-catalyzed decarboxylative oxidative addition, forming an electrophilic Pd π-allyl species and releasing an allylic alkoxide, which undergoes a Rh-catalyzed isomerization to an enolate in situ. Recombination of the Pd π-allyl species and Rh-enolate nucleophile then affords the α-quaternary carbonyl compound.

Kinetic and Dynamic Kinetic Resolution by Dual Catalysis

AbstractKinetic resolution is one of the most common methods to access enantiomerically enriched compounds. In this method, the resolution is based on the existing difference in reaction rates of the two enantiomers with a chiral catalyst. In the dynamic kinetic resolution, the less reactive enantiomer is racemized and the racemic mixture is further resolved, leading eventually to complete transformation to an enantioenriched compound. This review summarizes the dual catalytic strategies (i. e., modular combinations of distinct catalysts) that have been applied to kinetic resolution and dynamic kinetic resolution. We focus upon the role of the two catalysts, the compatibility between them, and the practical benefits.

Tuning Photoactive MIL-68(In) by Functionalized Ligands for Boosting Visible-Light Nitrogen Fixation.

In this work, MIL-68(In) functionalized with various ligand substitutions including amine, hydroxyl, bromine, nitro, and methyl groups was prepared, via a one-pot solvothermal reaction for visible-light photocatalytic ammonia synthesis. The diversity of ligands tunes the morphology, geometry, pore environment, and electronic structure of MIL-68(In)-based photocatalysts due to the polarity and intraframework interactions. Amine-inserted MIL-68(In) outperforms its counterparts, presenting a boosted nitrogen photofixation rate of 140.34 μmol gcat-1 h-1 with an apparent quantum efficiency of 5.69% at 420 nm. Further, the size of the batch solvothermal reactor and the amine group content also influence the photocatalytic activity. The combined experimental and theoretical results reveal that amine substituents improve the chemisorption of nitrogen molecules and the conversion of nitrogen into ammonia follows a dual pathway, i.e., a Mars-van Krevelen process and a ligand-to-metal charge transfer mechanism. This work provides a molecular engineering strategy via dual catalysis toward efficient ammonia production.

NIR-II Light Leveraged Dual Drug Synthesis for Orthotopic Combination Therapy.

Pd-catalyzed bioorthogonal bond cleavage reactions are widely used and frequently reported. It is circumscribed by low reaction efficiency, which may encumber the therapeutic outcome when applied to physiological environments. Herein, an NIR-II light promoted integrated catalyst (CuS@PDA/Pd) (PDA - polydopamine) is designed to accelerate the reaction efficiency and achieve a dual bioorthogonal reaction for combination therapy. As NIR-II light can penetrate deeply into tissue, the Pd-mediated cleavage reaction can be promoted both in vitro and in vivo by the photothermal properties of CuS, beneficial to orthotopic 4T1 tumor treatment. In addition, CuS also catalyzes the synthesis of active resveratrol analogs by the CuAAC reaction. These simultaneously produced anticancer agents result in enhanced antitumor cytotoxicity in comparison to the single treatments. This is a fascinating study to devise an integrated catalyst boosted by NIR-II light for dual bioorthogonal catalysis, which may provide the impetus for efficient bioorthogonal combination therapy in vivo.

Nucleophilic Addition of Benzylic and α-Heteroatom-Substituted Silanes to Aldehydes under Dual Catalysis

Key words benzylic silanes - chromium catalysis - dual catalysis - photoredox catalysis

Chromium/Photoredox Dual Catalyzed Synthesis of α-Benzylic Alcohols, Isochromanones, 1,2-Oxy Alcohols and 1,2-Thio Alcohols.

Herein, a Cr/Photoredox-catalyzed general synthetic strategy to access α-benzylic alcohols, isochromanones, oxy alcohols and thio alcohols is unveiled. Alkylation of aldehydes being a crucial C-C bond forming reaction, designing competent catalytic systems would render an attractive and decorated set of diverse alcohol motifs. Considering the challenges associated with classical organometallic chemistry, the strategy of dual catalysis is applied here to generate diverse alcohol motifs in a mild and efficient manner. The amalgamation of photocatalysis with chromium chemistry is chosen for this purpose to generate an environment with low basicity and thus, high chemoselectivity. With alkyl silanes as preferred coupling partners, this catalytic setup produces a broad substrate scope with an excellent functional group tolerance and displays a facile scale-up as well. Its application towards biologically relevant molecules and product diversification contributes to the synthetic utility of this method.

Multicomponent synthesis of α-chloro alkylboronic esters via visible-light-mediated dual catalysis

<h2>Summary</h2> α-Chloro alkylboronic (α-CAB) esters are a class of stable bifunctional molecules wherein the intrinsic differences of a carbon–chlorine and carbon–boron bond can be used to unlock distinct reactivity through carbon-electrophile, carbon-nucleophile, and carbon-centered radical intermediates. Despite their apparent utility, complex variants are not trivial to prepare via established methods. We present a new visible-light-mediated dual catalytic process for the multicomponent coupling of diaryliodonium salts, alkenes, and a simple metal chloride. The broad scope of the reaction combined with the capacity of their synthetic diversification will make this transformation attractive for practitioners of synthetic and medicinal chemistry in academic and industrial environments.

Photoredox-Ni Dual Catalysis: Chelation-Free Hydroacylation of Terminal Alkynes.

Hydroacylation of alkynes is undoubtedly the simplest and most atom-efficient approach for the synthesis of enones with diverse synthetic applications. Despite significant progress in hydroacylations, no hydroacylations exist that make use of aldehydes without a chelating group, especially when combined with terminal alkynes. Here we report a synergistic nickel-photocatalytic system that allows for the highly regio- and stereoselective hydroacylation of unactivated aldehydes and alkynes in milder conditions without the use of chelating groups.

Integrated nickel/polymer dual catalytic system for visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides

By merging transition metal and heterogeneous photocatalyst, a metal-photoredox system has attracted more attention for cross-coupling of various dual photoredox catalysis. However, there is a grand challenge for the attenuated nucleophilicity of sulfonamides relative to alkyl amines. Herein, an integrated dual catalytic system of porous carbon nitride nanosheet with nitrogen vacancies (N V -P-C 3 N 4 ) as a conjugated polymer semiconductor host in combination with transition-metal nickel (Ni) was constructed by a defect and morphology regulation strategy toward visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides. The excellent nickel/photoredox-catalyzed C–N coupling reaction performance is ascribed to the large specific surface area, abundant active sites, long carrier lifetime, and efficient transfer and separation of photoexcited electrons and holes. This work highlights the opportunity to cooperate with heterogeneous catalysts and active metal sites for challenging cross-coupling reactions. • Dual catalytic system of photoredox and transition metal • Carbon nitride with defect and morphology characteristics • C–N cross-coupling • Heterogeneous catalysts are used for sulfonamidation reactions For the fine chemical and pharmaceutical synthesis communities, it is crucial to determine the formation of anilines through C–N bond transformation approach. Considerable progress has been reported on dual catalytic systems of homogeneous photocatalysts combined with transition metals. However, the progress of heterogeneous catalysts for dual catalysis has not been satisfactory. Carbon nitride (C 3 N 4 ) is a class of metal-free conjugated polymer semiconductor with great potential for photoredox/Ni dual catalytic cross-couplings due to its thermal and chemical stability, facile fabrication, and cheapness. Herein, porous carbon nitride nanosheets with nitrogen vacancies (N V -P-C 3 N 4 ) were fabricated by a defect and morphology regulation strategy for visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides. This work highlights the opportunity to cooperate with heterogeneous catalysts and active metal sites for challenging cross-coupling reactions. An integrated dual catalytic system of N V -P-C 3 N 4 in combination with transition-metal Ni was constructed toward visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides. This work not only realizes the sulfonamidation reaction in a heterogeneous catalytic system for the first time but also demonstrates that defect engineering and morphology strategies are effective for enhancing photoredox dual catalytic performance.

Ionic Liquid Mediated Triple Catalysis for Alkylation and Methylation of Acyl Chlorides with Mechanistic Insight

Here we report a seminal triple catalysis strategy with the assistance of catalytic ionic liquid. DFT calculations reveal the detailed effect of ionic liquid in this triple catalysis mediated C(sp3)-H functionalizations and a very different mechanism has been established in contrast to all previous dual catalysis research. Based on it, direct coupling between acyl chlorides and very strong or polar C(sp3)-H bonds has been realized in high yields as well as unexpected methylation of acyl chlorides first using just 1.2 equivalent tetramethylsilane as methyl source via successive C(sp3)-H and C(sp3)-Si cleavage. One pot methylation strategy has been developed in this research. This is the first report of that ionic liquid is used for very strong C(sp3)-H bonds functionalization and the first report of that tetramethylsilane is used as methyl source.

Enantioselective Synthesis of N-Benzylic Heterocycles by Ni/Photoredox Dual Catalysis.

An asymmetric cross-coupling of α-N-heterocyclic trifluoroborates with aryl bromides using Ni/photoredox dual catalysis has been developed. This C(sp2)-C(sp3) cross-coupling provides access to pharmaceutically relevant chiral N-benzylic heterocycles in good to excellent enantioselectivity when bioxazolines (BiOX) are used as the chiral ligand. High-throughput experimentation significantly streamlined reaction development by identifying BiOX ligands for further investigation and by allowing for rapid optimization of conditions for new trifluoroborate salts.

Selective Reductive Coupling of Vinyl Azaarenes and Alkynes via Photoredox Cobalt Dual Catalysis.

A visible light-induced Co-catalyzed highly regio- and stereoselective reductive coupling of vinyl azaarenes and alkynes has been developed. Notably, Hünig's base together with simple ethanol has been successfully applied as the hydrogen sources instead of commonly used Hantzsch esters in this catalytic photoredox reaction. This approach has considerable advantages for the straightforward synthesis of stereodefined multiple substituted alkenes bearing an azaarene motif, such as excellent regioselectivity (>20 : 1 for >30 examples) and stereoselectivity (>20 : 1 E/Z), broad substrate scope and good functional group compatibility under mild reaction conditions, which has been utilized in the concise synthesis of natural product monomorine I. A reasonable catalytic reaction pathway involving protolysis of the cobaltacyclopentene intermediate has been proposed based on the mechanistic studies.

Selective Reductive Coupling of Vinyl Azaarenes and Alkynes via Photoredox Cobalt Dual Catalysis

AbstractA visible light‐induced Co‐catalyzed highly regio‐ and stereoselective reductive coupling of vinyl azaarenes and alkynes has been developed. Notably, Hünig's base together with simple ethanol has been successfully applied as the hydrogen sources instead of commonly used Hantzsch esters in this catalytic photoredox reaction. This approach has considerable advantages for the straightforward synthesis of stereodefined multiple substituted alkenes bearing an azaarene motif, such as excellent regioselectivity (&gt;20 : 1 for &gt;30 examples) and stereoselectivity (&gt;20 : 1 E/Z), broad substrate scope and good functional group compatibility under mild reaction conditions, which has been utilized in the concise synthesis of natural product monomorine I. A reasonable catalytic reaction pathway involving protolysis of the cobaltacyclopentene intermediate has been proposed based on the mechanistic studies.

Catalytic Multicomponent Synthesis ofC‐Acyl Glycosides by Consecutive Cross‐Electrophile Couplings

AbstractC‐Acyl glycosides are versatile intermediates to natural products and medicinally relevant entities. Conventional cross‐coupling strategies to secure these molecules often relied on two‐component manifolds in which a glycosyl precursor is coupled with an acyl donor (pre‐synthesized or generated in situ) under transition metal or dual catalysis to forge a C−C bond. Here, we disclose a three‐component Ni‐catalyzed reductive regime that facilitates the chemoselective union of glycosyl halides, organoiodides and commercially available isobutyl chloroformate as a CO surrogate. The method tolerates multiple functionalities and the resulting products are obtained in high diastereoselectivities. Theoretical calculations provide a mechanistic rationale for the unexpectedly high chemoselectivity of sequential cross‐electrophile couplings. This approach enables the expeditious assembly of difficult‐to‐synthesizeC‐acyl glycosides, as well as late‐stage keto‐glycosylation of oligopeptides.

Catalytic Multicomponent Synthesis of C-Acyl Glycosides by Consecutive Cross-Electrophile Couplings.

C-Acyl glycosides are versatile intermediates to natural products and medicinally relevant entities. Conventional cross-coupling strategies to secure these molecules often relied on two-component manifolds in which a glycosyl precursor is coupled with an acyl donor (pre-synthesized or generated in situ) under transition metal or dual catalysis to forge a C-C bond. Here, we disclose a three-component Ni-catalyzed reductive regime that facilitates the chemoselective union of glycosyl halides, organoiodides and commercially available isobutyl chloroformate as a CO surrogate. The method tolerates multiple functionalities and the resulting products are obtained in high diastereoselectivities. Theoretical calculations provide a mechanistic rationale for the unexpectedly high chemoselectivity of sequential cross-electrophile couplings. This approach enables the expeditious assembly of difficult-to-synthesize C-acyl glycosides, as well as late-stage keto-glycosylation of oligopeptides.

Electrochemical Rhodium-Catalyzed C-H Cyclodimerization of Alkynes to Access Diverse Functionalized Naphthalenes: Involvement of RhIV/V and RhI Dual Catalysis.

The first electrochemical rhodium-catalyzed C-H cyclodimerization of alkynes for the direct construction of functionalized naphthalenes was reported. The practicality and synthetic value of this strategy were demonstrated by the readily accessible scale-up synthesis and transformation of the products. Detailed mechanistic studies evidenced that electricity played an important role during the electrochemical disproportionation (ECD) process to generate and maintain the catalytically active RhIV/V and RhI species, which conducted the direct C-H activation.

Polymeric multimaterials by photochemical patterning of crystallinity.

An organized combination of stiff and elastic domains within a single material can synergistically tailor bulk mechanical properties. However, synthetic methods to achieve such sophisticated architectures remain elusive. We report a rapid, facile, and environmentally benign method to pattern strong and stiff semicrystalline phases within soft and elastic matrices using stereo-controlled ring-opening metathesis polymerization of an industrial monomer, cis-cyclooctene. Dual polymerization catalysis dictates polyolefin backbone chemistry, which enables patterning of compositionally uniform materials with seamless stiff and elastic interfaces. Visible light-induced activation of a metathesis catalyst results in the formation of semicrystalline trans polyoctenamer rubber, outcompeting the formation of cis polyoctenamer rubber, which occurs at room temperature. This bottom-up approach provides a method for manufacturing polymeric materials with promising applications in soft optoelectronics and robotics.

Shining Visible Light on Reductive Elimination: Acridine-Pd-Catalyzed Cross-Coupling of Aryl Halides with Carboxylic Acids.

Despite the recent tremendous progress on transition-metal/photoredox dual catalysis in organic synthesis, single transition-metal catalysis under visible-light irradiation, which can utilize light energy more efficiently, is still underdeveloped. Herein, we report the design of photosensitizing phosphinoacridine bidentate ligands for visible-light-induced transition-metal catalysis, expecting that the electron-accepting acridine moiety would create a highly reactive electron-deficient metal center toward reductive elimination via metal-to-ligand charge transfer (MLCT). Using these ligands, we have achieved a palladium-catalyzed cross-coupling reaction of aryl halides with carboxylic acids under visible-light irradiation. Electronic tuning of the phosphinoacridine ligands not only enabled the use of a variety of aryl halides as the coupling partner, including less reactive aryl chlorides, under blue light irradiation, but also realized the employment of lower-energy green and red light for the cross-coupling. Experimental mechanistic studies have proved that the reductive elimination of aryl esters is induced by photoirradiation of phosphinoacridine-ligated arylpalladium(II) carboxylate complexes. The theoretical calculation suggests that the reductive elimination in the excited state is promoted by decreasing the electron density of the Pd center through photoinduced intramolecular electron transfer, i.e., MLCT, in the transition state owing to the electron-deficient acridine scaffold. This is a very rare example of photoinduced reductive elimination on palladium(II) complexes.

CuX Dual Catalysis: Construction of Oxazolo[2,3-b][1,3]oxazines via a Tandem CuAAC/Ring Cleavage/[4+2+3] Annulation Reaction.

CuX as a simple dual catalyst strategy that promotes the tandem transformations of fused oxazolo[2,3-b][1,3]oxazines has been developed. Copper catalyzed terminal ynones, sulfonyl azides, and nitriles for the CuAAC/ring cleavage/[4+2] annulation reaction, while the halogen catalyzed ring cleavage and [2+3] annulation of oxiranes to form the final fused products. This study provides a four-component, one-pot strategy for synthesizing complex fused heterocycles from simple ingredients and expands the application of CuAAC in organic synthesis.