Dual Catalysis Research Articles

Access to Trifluoromethylketones from Alkyl Bromides and Trifluoroacetic Anhydride by Photocatalysis

AbstractAliphatic trifluoromethyl ketones are a type of unique fluorine‐containing subunit which play a significant role in altering the physical and biological properties of molecules. Catalytic methods to provide direct access to aliphatic trifluoromethyl ketones are highly desirable yet remain underdeveloped, partially owing to the high reactivity and instability of trifluoroacetyl radical. Herein, we report a photocatalytic synthesis of trifluoromethyl ketones from alkyl bromides with trifluoroacetic anhydride. The reaction features dual visible‐light and halogen‐atom‐transfer catalysis, followed by an enabling radical‐radical cross‐coupling of an alkyl radical with a stabilized trifluoromethyl radical. The reaction provides straightforward access to aliphatic trifluoromethyl ketones from readily available and cost‐effective alkyl halides and trifluoroacetic anhydride (TFAA).

Access to Trifluoromethylketones from Alkyl Bromides and Trifluoroacetic Anhydride by Photocatalysis.

Aliphatic trifluoromethyl ketones are a type of unique fluorine-containing subunit which plays a significant role in altering the physical and biological properties of molecules. However, catalytic methods to provide direct access to aliphatic trifluoromethyl ketones is highly desirable yet remains underdeveloped, partially due to the high reactivity and instability of trifluoroacetyl radical. Herein, we report a photocatalytic synthesis of trifluoromethyl ketones from alkyl bromides with trifluoroacetic anhydride. The reaction features a dual catalysis of visible-light and XAT reaction, followed by an enabling radical-radical cross-coupling of alkyl radical with a stabilized trifluoromethyl radical. The reaction provides the first straightforward access to aliphatic trifluoromethyl ketones from easily-available and cost-effective alkyl halides and TFAA.

Tannic acid-Fe3+ dual catalysis induced rapid polymerization of injectable poly(lysine) hydrogel for infected wound healing

Infected wounds are difficult to heal because they are vulnerable to bacterial attacks, inflammatory responses, and oxidative stress. To promote the healing of infected wounds, we developed an injectable dual-network hydrogel TFAEP (TA-Fe, APS, EPL-GMA, PVA) based on ε-poly-l-lysine-graft-glycidyl methacrylate (EPL-GMA), polyvinyl alcohol (PVA), and tannic acid-iron (TA-Fe). TA-Fe formed a stable redox pair, which acted as a dual-autocatalytic system to activate ammonium persulfate, generate free radicals, and subsequently induce EPL-GMA polymerization. Then PVA formed hydrogen bonds with TA molecules. Here, TA-Fe not only simulated peroxidase to convert H2O2 into hydroxyl radicals (OH), but also exhibited good near-infrared photothermal conversion efficiency, which all endowed the hydrogel with excellent antibacterial ability. In addition, the hydrogel could remove excessive reactive oxygen species and reactive nitrogen species, alleviating oxidative stress and reducing inflammation response due to the presence of TA molecules. Moreover, the hydrogel showed good injectability and tissue adhesion, ensuring the close adhesion of the hydrogel to the wound and achieving the maximum function. In vivo experiments demonstrated that the hydrogel promoted infected wound healing by accelerating epidermal regeneration, promoting angiogenesis and collagen deposition, and facilitating the expression of anti-inflammatory factors.

Recent Advances and Development in Visible‐Light‐Mediated Glycosylation: An Expanding Research Area in Glycochemistry

AbstractIn the last fifteen years, the development of visible‐light photocatalysis, metal/photoredox dual catalysis has become the forefront as a new paradigm in organic synthesis as well as in carbohydrate chemistry. It led to the discovery of unprecedented transformations and also the improvement of known reactions under mild conditions, employing simple household light sources and bench‐stable precursors, which meet the requirements of green chemistry and sustainable development in excellent yield and stereocontrol. In a general sense, the exploitation of photoredox catalysis hinges on the capability of photocatalyst or redox mediator to transform visible light into chemical energy via photo‐irradiated SET (single electron transfer), PET (photoinduced electron transfer), HAT (hydrogen atom transfer), and XAT (halogen atom transfer) to potentially unlock unique reaction pathways, thereby generating a diverse array of reactive intermediates. In view of reaction type, mechanism, and status, this review will systematically summarize the latest advances in visible‐light‐promoted photocatalytic glycosylation reactions, which are driven by single or dual photoredox catalysis and by the photoactivity of electron donor‐acceptor (EDA) complexes.

Developing Organometallic Nucleophilic Reagents Via Photoredox Catalysis

AbstractThe addition of organometallic reagents to the carbonyl group represents a key transformation, both in academia and industry. Most of these transformations rely on a mechanism in which accessible and reactive halides are transformed into the corresponding nucleophilic organometallic reactive compounds through a redox mechanism, using a metal (Cr, Mg, In, etc.) in low oxidation state, by electron transfer. With the advent of photoredox catalysis, the formation of radicals, through oxidation or reduction of suitable and tailored organic precursors, was merged with transition metal catalysis. By radical-to-polar crossover (RPCO­), a radical metal is combined with an organic radical to produce, via radical-radical trapping, a polar nucleophilic organometallic reagent. Using dual photoredox catalysis (metallaphotoredox catalysis), a reactive organometallic reagent can be prepared, avoiding the use of metals in low oxidation state. Herein, in addition to the description of the results obtained by our group and the contributions of others on the connection between carbonyl addition and radical-based photochemistry, we provide core guidance for further synthetic developments. We anticipate that extending the photoredox dual strategy beyond the Barbier reactions described here, taming less-activated carbonyls, studying other important electrophiles, will soon realize important breakthroughs.1 Introduction2 Photoredox Catalysis: A Survival Guide for the ‘Photo-Curious’3 Chromium Nucleophilic Organometallic Reagents3.1 Allylation of Aldehydes3.2 Allylation of Aldehydes via Dienes3.3 Propargylation of Aldehydes via 1,3-Enynes3.4 Alkenylation of Aldehydes3.5 Alkylation of Aldehydes3.6 Enantioselective Chromium-Mediated Photoredox Reactions4 Titanium Nucleophilic Organometallic Reagents4.1 Allylation Reactions4.2 Propargylation Reactions4.3 Allylation Reactions via Dienes4.4 Benzylation Reactions4.5 Alkylation Reactions5. Cobalt Nucleophilic Organometallic Reagents5.1 Allylation Reactions6 Conclusion

Recent Advances in Carbonyl‐Photoredox/Transition Metal Dual Catalysis

AbstractOrganic transformations using carbonyl‐photoredox/metal dual catalysis have attracted much attention in recent years. Abundant and inexpensive carbonyl photosensitizers effectively serve as single electron, energy or hydrogen atom transfer agents to induce metal‐catalyzed cross‐coupling and dicarbofunctionalization of olefins. This review covers literature reports of metal‐catalyzed photocatalytic coupling reactions from 2020 to mid‐2023, with a focus on C−C (C(sp3)−C(sp3), C(sp3)−C(sp2), C(sp2)−C(sp2), C(sp2)−C(sp)) and C‐heteroatom (C(sp3)−S, C(sp3)−N, C(sp2)−O, C(sp2)−S, C(sp2)−P, C(sp2)−B) bond forming reactions.

Carbon Vacancies Steer the Activity in Dual Ni Carbon Nitride Photocatalysis.

The manipulation of carbon nitride (CN) structures is one main avenue to enhance the activity of CN-based photocatalysts. Increasing the efficiency of photocatalytic heterogeneous materials is a critical step toward the realistic implementation of sustainable schemes for organic synthesis. However, limited knowledge of the structure/activity relationship in relation to subtle structural variations prevents a fully rational design of new photocatalytic materials, limiting practical applications. Here, the CN structure is engineered by means of a microwave treatment, and the structure of the material is shaped around its suitable functionality for Ni dual photocatalysis, with a resulting boosting of the reaction efficiency toward many CX (X = N, S, O) couplings. The combination of advanced characterization techniques and first-principle simulations reveals that this enhanced reactivity is due to the formation of carbon vacancies that evolve into triazole and imine N species able to suitably bind Ni complexes and harness highly efficient dual catalysis. The cost-effective microwave treatment proposed here appears as a versatile and sustainable approach to the design of CN-based photocatalysts for a wide range of industrially relevant organic synthetic reactions.

1,2‐Arylsulfonylation of Vinyl Ethers and Esters Enabled by Dual Ni Catalysis

AbstractA dual photocatalytic sulfonylation‐arylation of electron‐rich alkenes is described. By combining sulfinate salts, (hetero)‐aryl‐bromides and 2,3‐dihydrofuran under Ru and Ni dual catalysis, over 35 examples of aryl‐sulfonylated scaffolds could be obtained in good to excellent yields, under mild reaction conditions and high diastereoselectivity.

Highly Sensitive Detection of Bacteria by Binder-Coupled Multifunctional Polymeric Dyes.

Infectious diseases caused by pathogens are a health burden, but traditional pathogen identification methods are complex and time-consuming. In this work, we have developed well-defined, multifunctional copolymers with rhodamine B dye synthesized by atom transfer radical polymerization (ATRP) using fully oxygen-tolerant photoredox/copper dual catalysis. ATRP enabled the efficient synthesis of copolymers with multiple fluorescent dyes from a biotin-functionalized initiator. Biotinylated dye copolymers were conjugated to antibody (Ab) or cell-wall binding domain (CBD), resulting in a highly fluorescent polymeric dye-binder complex. We showed that the unique combination of multifunctional polymeric dyes and strain-specific Ab or CBD exhibited both enhanced fluorescence and target selectivity for bioimaging of Staphylococcus aureus by flow cytometry and confocal microscopy. The ATRP-derived polymeric dyes have the potential as biosensors for the detection of target DNA, protein, or bacteria, as well as bioimaging.

Photoredox/Palladium Dual Catalysis for Site-Selective C-H Arylation and Acylation of N-Protected Carbazoles in Visible Light.

An unprecedented C-1 selective mono-arylation/acylation of N-protected carbazoles with aryl diazonium salts/glyoxylic acids has been developed in visible light by dual catalytic system comprising of Eosin Y and palladium acetate. The methodology has good functional group tolerance and high regioselectivity and furnishes the monosubstituted products in moderate to good yields at room temperature.

Computational Mechanistic Study on Intramolecular Triple Cyclization of 1-Biphenylethynyl-2-phenylethynylbenzenes Giving Spiro Fluorene-Phenylenevinylenes by Dual Catalysis

Abstract Cationic Au(I) complex-catalyzed double cyclizations of 1,2-dialkynylbenzene derivatives are valuable for the straightforward synthesis of ladder-type π-conjugated compounds. We have previously developed a method for synthesizing ladder-type π-conjugated molecules with spiro skeleton (spiro fluorene-phenylene vinylenes) by the triple cyclization of 1-biphenylethynyl-2-phenylethynylbenzenes using an AuCl(SMe2)/tBuXPhos/AgNTf2 catalyst system. Experimental mechanistic studies revealed that an Ag(I) complex or HNTf2, as well as a cationic Au(I) complex, catalyzes different reaction steps. However, detailed insight into which of the Ag(I) complex or HNTf2 functions as the actual cocatalyst and the origin of the selectivity of the reaction have not been elucidated. Here we report a detailed reaction mechanism for this triple cyclization by dual catalysis based on computational studies. A cationic Au(I) complex catalyzes the first and second cyclization steps, whose regioselectivity is thermodynamically and kinetically controlled. The third spirocyclization step to construct a spirocenter is catalyzed by in situ generated HNTf2 rather than an Au(I) or Ag(I) complex via a benzyl cation intermediate. The present Au(I)/Brønsted acid dual-catalyzed mechanism of the triple cyclization of 1-biphenylethynyl-2-phenylethynylbenzenes provides complimentary activation modes to the conventionally used single Au(I)-catalyzed one.

Rh(II)/Pd(0) Dual Catalysis: Interception of Ammonium Ylide with Allyl Palladium to Construct 2,2-Disubstituted Tetrahydroquinoline Derivatives.

New synthetic methods to construct 2,2-disubstituted tetrahydroquinoline derivatives are of significant value in pharmaceutical chemistry. Herein, a Rh(II)/Pd(0) dual-catalyzed diazo α-aminoallylation reaction has been developed between allylpalladium(II) and ammonium ylides derived from the Rh2(OAc)4-mediated intramolecular N-H bond insertion reaction of diazo compounds, affording various 2,2-disubstituted tetrahydroquinoline derivatives in good yields up to 93% with high chemoselectivities under mild reaction conditions. A substrate scope investigation reveals broad ester substituent tolerance, and control experiments provide the basis for a proposed reaction mechanism.

Migratory allylic arylation of 1,n-enols enabled by nickel catalysis

Transition-metal-catalyzed allylic substitution reactions (Tsuji−Trost reactions) proceeding via a π-allyl metal intermediate have been demonstrated as a powerful tool in synthetic chemistry. Herein, we disclose an unprecedented π-allyl metal species migration, walking on the carbon chain involving 1,4-hydride shift as confirmed by deuterium labeling experiments. This migratory allylic arylation can be realized under dual catalysis of nickel and lanthanide triflate, a Lewis acid. Olefin migration has been observed to preferentially occur with the substrate of 1,n-enols (n ≥ 3). The robust nature of the allylic substitution strategy is reflected by a broad scope of substrates with the control of regio- and stereoselectivity. DFT studies suggest that π-allyl metal species migration consists of the sequential β-H elimination and migratory insertion, with diene not being allowed to release from the metal center before producing a new π-allyl nickel species.

Radical Coupling Initiated by Organophosphine Addition to Ynoates.

Dual nucleophilic phosphine photoredox catalysis is yet to be developed due to facile oxidation of the phosphine organocatalyst to the phosphoranyl radical cation. Herein, we report a reaction design that avoids this event and exploits traditional nucleophilic phosphine organocatalysis with photoredox catalysis to allow the Giese coupling with ynoates. The approach has good generality, while its mechanism is supported by cyclic voltametric, Stern-Volmer quenching, and interception studies.

Molecular Insights into Photochemical Hydrogen Evolution Dual Catalysis within the Shell of Polymer Micelle-Based Nanoreactors

Polymer micelles are promising candidates for facilitating efficient catalysis within their distinguished nanospaces. However, the design of polymer micelle-based nanoreactors for dual photocatalysis, where a photocatalyst and another catalyst are involved in a single catalysis, remains limited in scope due to the lack of molecular insight into the bimolecular process within polymer micelles. Here, we investigated the cooperativity of a photocatalyst and a hydrogen evolution catalyst immobilized within the shell of polymer micelle-based nanoreactors. The results of several photochemical experiments suggested the existence of two types of catalyst pairs, the fluctuated and contacted pairs of the photocatalyst and hydrogen evolution catalyst within the nanoreactors. Moreover, the reaction rates of the photochemical hydrogen evolution were strongly affected by molecular crowding within the shell. Our study paves the way for developing polymer micelle-based nanoreactors for efficient dual photocatalysis.

Light-assisted dual catalysis for C–N bond construction

Combining photo-assisted technologies with varying catalysis is of significance for the integration of multiple conversion routes to access value-added chemicals. Recent advances in the development of dual catalytic systems highlight the remarkable synergy of photocatalytic processes with thermo-, bio-, or electrocatalysis to construct the versatile C–N bond for valuable nitrogen-containing organic molecules.

Intermolecular 1,2-Difunctionalization of Terminal Alkynes to Access Trisubstituted Alkenes via Copper/Photoredox Dual Catalysis.

We report a copper metallaphotocatalytic 1,2-difunctionalization of terminal alkynes with N-hydroxyphthalimide (NHP) esters and readily available silyl reagents (TMSCN and TMSNCS) to access stereodefined trisubstituted alkenes, including (E)-alkenyl nitriles and thiocyanates. The reaction proceeds with excellent anti-stereoselectivity and demonstrates broad compatibility with a wide range of terminal alkynes and NHP esters as alkyl radical precursors. Experimental and computational studies have been performed to gain insight into the reaction mechanism.

α‐C−H Arylation of N‐Sulfonyl Amines by Dual Palladium Catalysis

AbstractFunctionalization of C(sp3)−H bonds adjacent to a nitrogen atom is an efficient means of preparing structurally complex amines and has long been of interest to synthetic chemists. Herein, dual palladium catalysis is used to achieve α‐C−H arylation of linear N‐sulfonyl amines with aryl boroxines, rather than N‐arylation (C−N bond formation). This method has a broad scope with respect to both the amine and the boroxine, providing convenient access to α‐branched amines. During the dehydrogenation step of the catalytic cycle, bromobenzene accepts a hydride from the α‐carbon on the amine, producing an imine that subsequently undergoes Pd‐catalyzed C‐arylation with the boroxine. Mechanistic studies revealed that imine arylation proceeds through an unusual Pd0/PdII catalytic cycle, in which oxidative cyclization of a palladium η2‐imine complex generates a three‐membered palladacycle that subsequently undergoes transmetallation reaction with the boroxine.

Photocatalytic Metal Hydride Hydrogen Atom Transfer Mediated Allene Functionalization by Cobalt and Titanium Dual Catalysis

AbstractCatalytic metal hydride hydrogen atom transfer (MHAT) reactions have proven to be a powerful method for alkene functionalization. This work reports the discovery of Co‐porphines as highly efficient MHAT catalysts with a loading of only 0.01 mol % for unprecedented chemoselective allene functionalization under photoirradiation. Moreover, the newly developed bimetallic strategy by the combination of photo Co‐MHAT and Ti catalysis enabled the successful carbonyl allylation with a wide range of amino, oxy, thio, aryl, and alkyl‐allenes providing expedient access to valuable β‐functionalized homoallylic alcohols in over 100 examples with exceptional regio‐ and diastereoselectivity. Mechanism studies and DFT calculations supported that selectively transferring hydrogen atoms from cobalt hydride to allenes and generating allyl radicals is the key step in the catalytic cycle.

Photocatalytic Metal Hydride Hydrogen Atom Transfer Mediated Allene Functionalization by Cobalt and Titanium Dual Catalysis.

Catalytic metal hydride hydrogen atom transfer (MHAT) reactions have proven to be a powerful method for alkene functionalization. This work reports the discovery of Co-porphines as highly efficient MHAT catalysts with a loading of only 0.01 mol % for unprecedented chemoselective allene functionalization under photoirradiation. Moreover, the newly developed bimetallic strategy by the combination of photo Co-MHAT and Ti catalysis enabled the successful carbonyl allylation with a wide range of amino, oxy, thio, aryl, and alkyl-allenes providing expedient access to valuable β-functionalized homoallylic alcohols in over 100 examples with exceptional regio- and diastereoselectivity. Mechanism studies and DFT calculations supported that selectively transferring hydrogen atoms from cobalt hydride to allenes and generating allyl radicals is the key step in the catalytic cycle.