Palladium-Catalyzed Decarboxylative Annulation Reaction of Aryl Iodides and Methyl 2-Haloarenecarboxylates

A ligand-free palladium-catalyzed and norbornadiene-mediated annulation reaction of iodoarenes with methyl 2-haloarenecarboxylates is reported. The sequentially accomplished reaction comprises intermolecular C-H arylation, followed by intramolecular decarboxylative annulation, affording various valuable phenanthrenes. This reaction protocol could be expanded to triphenylene syntheses whereby norbornene was the cocatalyst. Interestingly, the decarboxylation of methyl esters was accomplished via solvent-mediated CMe-O bond cleavages.

Sulfur-Mediated Decarboxylative Amidation of Cinnamic Acids via C═C Bond Cleavage

A new strategy for the synthesis of amides has been developed using sulfur-mediated decarboxylative coupling of cinnamic acids with amines via oxidative cleavage of the C═C bond.

Ni-Catalyzed Reductive 1,2-Alkylarylation of Alkenes for the Synthesis of Spirocyclic γ-Lactams

An intermolecular nickel-catalyzed reductive 1,2-alkylarylation of acrylates with cyclopropylamine NHP esters and aryl iodides is reported. This operationally simple protocol provides direct access to 1-alkylcyclopropylamine scaffolds. The mild conditions are compatible with four-membered α-amino strained rings as well as five- and six-membered ring systems. The products undergo cyclization to access α-arylated spirocyclic γ-lactams─a motif present in several pharmaceuticals.

Palladium-catalyzed Suzuki-Miyaura cross-coupling of carboxylic-phosphoric anhydrides via C-O bond cleavage

A robust palladium-catalyzed Suzuki-Miyaura reaction of carboxylic-phosphoric anhydrides via highly selective C(O)-O bond cleavage under inorganic base-free conditions has been reported. Carboxylic-phosphoric anhydrides, generated through activating carboxylic acids using phosphates by esterification or direct dehydrogenative reaction with phosphites, have been employed as highly reactive electrophiles for Suzuki-Miyaura cross-coupling reactions. Broad substrate scope and excellent functional group tolerance have been demonstrated to be a general and practical approach for the synthesis of highly valuable ketones.

Transition metal-free decarboxylative olefination of carboxylic acid salts

The cost-effective and efficient synthesis of alkenes is highly significant due to their extensive applications in both synthetic and polymer industries. A transition metal-free approach has been devised for the chemoselective olefination of carboxylic acid salts. This modular approach provides direct access to valuable electron-deficient styrenes in moderate to good yields. Detailed mechanistic studies suggest anionic decarboxylation is followed by halogen ion transfer. This halogen transfer leads to an umpolung of reactant electronics, allowing for a rate-limiting rebound elimination.

Decarboxylative Aldol Reaction of α,α-Difluoro-β-keto Esters: Easy Access to Difluoroenolate

Yb(OTf)3 promoted the Krapcho decarboxylation of 2,2-difluoro-3-oxopropanoate, and a subsequent aldol reaction was achieved. This process is the first example of generating difluoroenolates through a decarboxylation-type process, and a large number of carbonyl compounds are applicable to the aldol reaction. The protocol is a complete one-pot reaction that uses the bench-stable and nonhygroscopic 2,2-difluoro-3-oxopropanoate to generate the difluoroenolate. This strategy has been applied for the synthesis of CF2-containing bioactive GABAB agonists, contributing to drug design.

Divergent Transformations of Aromatic Esters: Decarbonylative Coupling, Ester Dance, Aryl Exchange, and Deoxygenative Coupling

ConspectusAromatic esters are cost-effective, versatile, and commonly used scaffolds that are readily synthesized or encountered as synthetic intermediates. While most conventional reactions involving these esters are nucleophilic acyl substitutions or 1,2-nucleophilic additions─where a nucleophile attacks the carbonyl group, decarbonylative transformations offer an alternative pathway by using the carbonyl group as a leaving group. This transition-metal-catalyzed process typically begins with oxidative addition of the C(acyl)-O bond to the metal. Subsequently, the reaction involves the migration of CO to the metal center, the reaction with a nucleophile, and reductive elimination to yield the final product. Pioneering work by Yamamoto on nickel complexes and the development of decarbonylative reactions (such as Mizoroki-Heck-type olefination) using aromatic carboxylic anhydrides catalyzed by palladium were conducted by de Vries and Stephan. Furthermore, reports have surfaced of decarbonylative hydrogenation of pyridyl methyl esters by Murai using ruthenium catalysts as well as Mizoroki-Heck-type reactions of nitro phenyl esters by Gooßen under palladium catalysis. Our group has been at the forefront of developing decarbonylative C-H arylations of phenyl esters with 1,3-azoles and aryl boronic acids using nickel catalysts. The key to this reaction is the use of phenyl esters, which are easy to synthesize, stabilize, and handle, allowing oxidative addition of the C(acyl)-O bond; nickel, which facilitates oxidative addition of the C(acyl)-O bond; and suitable bidentate phosphine ligands that can stabilize the intermediate. By modification of the nucleophiles, esters have been effectively utilized as electrophiles in cross-coupling reactions, encouraging the development of these nucleophiles among researchers. This Account summarizes our advancements in nucleophile development for decarbonylative coupling reactions, particularly highlighting the utilization of aromatic esters in diverse reactions such as alkenylation, intramolecular etherification, α-arylation of ketones, C-H arylation, methylation, and intramolecular C-H arylation for dibenzofuran synthesis, along with cyanation and reductive coupling. We also delve into reaction types that are distinct from typical decarbonylative reactions, including ester dance reactions, aromatic ring exchanges, and deoxygenative transformations, by focusing on the oxidative addition of the C(acyl)-O bond of the aromatic esters to the metal complex. For example, the ester dance reaction is hypothesized to undergo 1,2-translocation starting with oxidative addition to a palladium complex, leading to a sequence of ortho-deprotonation/decarbonylation, followed by protonation, carbonylation, and reductive elimination. The aromatic exchange reaction likely involves oxidative addition of complexes of different aryl electrophiles with a nickel complex. In deoxygenative coupling, an oxidative addition complex with palladium engages with a nucleophile, forming an acyl intermediate that undergoes reductive elimination in the presence of an appropriate reducing agent. These methodologies are poised to captivate the interest of synthetic chemists by offering unconventional and emerging approaches for transforming aromatic esters. Moreover, we demonstrated the potential to transform readily available basic chemicals into new compounds through organic synthesis.

Unimolecular Fragment Coupling: A New Bond-Forming Methodology via the Deletion of Atom(s)

Unimolecular fragment coupling (UFC) is defined as a reaction format, wherein atom(s) located in the middle of a molecule are extruded, and the remaining fragments are coupled. UFC is a potentially powerful strategy that is an alternative to transition-metal-catalyzed cross-coupling because the target chemical bond is formed in an intramolecular fashion, which is inherently beneficial for chemoselectivity and stereoselectivity issues. In this Perspective, we will present an overview of the recent advances in UFC reactions, which encompass those proceeding through the elimination of CO2, CO, SO2, isocyanates, N2, or single atoms primarily via transition metal catalysis.

Pd-Catalyzed Decarbonylative sp2 C-H Arylation: Construction of Five- and Six-Membered (Hetero)Cyclic Compounds

The cyclic compounds have wide applications in the design and synthesis of drugs and materials; thus, their efficient construction attracts much attention from the synthetic community. In this letter, we report an efficient method for preparing cyclic compounds starting from the readily available carboxylic acids. This reaction takes place through intramolecular decarbonylative sp2 C-H arylation, enabling efficient synthesis of a wide range of five- and six-membered cyclic compounds. Both carbo- and heterocycles can be produced under the reaction conditions. Moreover, this reaction features a wide substrate scope with high functional group tolerance. The scale-up experiments also show its practicality in organic synthesis. Those experimental results indicate that this reaction would find wide applications in the synthetic community.

Decarboxylative Nucleophilic Fluorination of Aliphatic Carboxylic Acids

Herein, we present a decarboxylative nucleophilic fluorination of carboxylic acids with a silver catalyst. This strategy enables the synthesis of a myriad of diverse and valuable fluorinated motifs under mild conditions, demonstrating good functional-group tolerance and utility in late-stage functionalization. In contrast to traditional electrophilic fluorination, this nucleophilic method utilizes a more readily available nucleophilic fluorinating reagent, providing substantial advantages in terms of cost efficiency, broad substrate scope, and functional-group compatibility.

Decarboxylative stereoretentive C-N coupling by harnessing aminating reagent

In recent decades, strategies involving transition-metal catalyzed carbon-carbon or carbon-heteroatom bond coupling have emerged as potent synthetic tools for constructing intricate molecular architectures. Among these, decarboxylative carbon-nitrogen bond formation using abundant carboxylic acids or their derivatives has garnered notable attention for accessing alkyl- or arylamines, one of key pharmacophores. While several decarboxylative amination methods have been developed, the involvement of a common carboradical intermediate currently poses challenges in achieving stereospecific transformation toward chiral alkylamines. Herein, we present a base-mediated, stereoretentive decarboxylative amidation by harnessing 1,4,2-dioxazol-5-one as a reactive and robust amidating reagent under transition-metal-free ambient conditions, encompassing all types of primary, secondary and tertiary carboxylic acids, thereby providing access to the important pharmacophore, α-chiral amines. This method exhibits high functional group tolerance, convenient scalability, and ease of applicability for 15N-isotope labeling, thus accentuating its synthetic utilities. Experimental and computational mechanistic investigations reveal a sequence of elementary steps: i) nucleophilic addition of carboxylate to dioxazolone, ii) rearrangement to form a dicarbonyl N-hydroxy intermediate, iii) conversion to hydroxamate, followed by a Lossen-type rearrangement, and finally, iv) reaction of the in situ generated isocyanate with carboxylate leading to C-N bond formation in a stereoretentive manner.

Iridium(III)-catalyzed photoredox cross-coupling of alkyl bromides with trialkyl amines: access to α-alkylated aldehydes

A C(sp3)-C(sp3) cross coupling approach based on an iridium-photocatalytic radical process has been developed enabling the synthesis of various α-alkylated aldehydes from easily available/synthesized alkyl bromides and trialkyl amines under mild photocatalytic conditions. The synthesized aldehydes are also explored as a functional handle for various useful products such as carboxylic acid, alcohol and N-heterocycle synthesis.

Decarboxylative Ketonization of Aliphatic Carboxylic Acids in a Continuous Flow Reactor Catalysed by Manganese Oxide on Silica

The sustainable synthesis of long carbon chain molecules from carbon dioxide, water and electricity relies on the development of waste-free, highly selective C-C bond forming reactions. An example for such a power-to-chemicals process is the industrial-scale fermentation for the production of hexanoic acid. Herein, we describe how this product is transformed into 6-undecanone via decarboxylative ketonization using a heterogeneous manganese oxide/silica catalyst. The reaction reaches full conversion with near-complete selectivity when carried out in a continuous flow reactor, requires no solvent or carrier gas, and releases carbon dioxide and water as the only by-products. The reactor was operated for several weeks with no loss of reactivity, producing 7 kg of 6-undecanone from 10 g of catalyst and achieving a productivity of 1.135 kg per litre of reactor volume per hour. 6-Undecanone and other long-chain ketones accessible this way can be hydrogenated to industrially meaningful alkanes, or converted into valuable fatty acids via a hydrogenation/elimination/isomerizing hydrocarboxylation sequence.

Palladium-Catalyzed Deuteration of Arylketone Oxime Ethers

We report herein the development of palladium-catalyzed deacylative deuteration of arylketone oxime ethers. This protocol features excellent functional group tolerance, heterocyclic compatibility, and high deuterium incorporation levels. Regioselective deuteration of some biologically important drugs and natural products are showcased via Friedel-Crafts acylation and subsequent deacylative deuteration. Vicinal meta-C-H bond functionalization (including fluorination, arylation, and alkylation) and para-C-H bond deuteration of electro-rich arenes are realized by using the ketone as both directing group and leaving group, which is distinct from aryl halide in conventional dehalogenative deuteration.

Ligand Relay for Nickel-Catalyzed Decarbonylative Alkylation of Aroyl Chlorides

Transition metal-catalyzed direct decarboxylative transformations of aromatic carboxylic acids usually require high temperatures, which limit the substrate's scope, especially for late-stage applications. The development of the selective decarbonylative of carboxylic acid derivatives, especially the most fundamental aroyl chlorides, with stable and cheap electrophiles under mild conditions is highly desirable and meaningful, but remains challenging. Herein, a strategy of nickel-catalyzed decarbonylative alkylation of aroyl chlorides via phosphine/nitrogen ligand relay is reported. The simple phosphine ligand is found essential for the decarbonylation step, while the nitrogen ligand promotes the cross-electrophile coupling. Such a ligand relay system can effectively and orderly carry out the catalytic process at room temperature, utilizing easily available aroyl chlorides as an aryl electrophile for reductive alkylation. This discovery provides a new strategy for direct decarbonylative coupling, features operationally simple, mild conditions, and excellent functional group tolerance. The mild approach is applied to the late-stage methylation of various pharmaceuticals. Extensive experiments are carried out to provide insights into the reaction pathway and support the ligand relay process.

Decarbonylative borylation of aryl anhydrides via rhodium catalysis

Decarbonylative borylation of aryl anhydrides by rhodium catalysis has been reported. A base-free system with Rh(PPh3)3Cl as a catalyst enables the efficient synthesis of various arylboronate esters from readily available aryl anhydrides. The reaction involves the cleavage of C(O)-O bonds and the formation of C-B bonds. The experimental results demonstrated that compared with carboxylic acids, amides, and esters, anhydrides have higher reactivity in the decarbonylative borylation reaction under the current conditions. Furthermore, compared with the reported palladium-catalyzed borylation reaction of aryl anhydrides, the present rhodium-catalyzed method has the advantages of a shorter reaction time and a lower reaction temperature.

Palladium-Catalyzed Decarbonylative Sonogashira Alkynylation of Carboxylic-Phosphoric Anhydrides

We report the first palladium-catalyzed decarbonylative alkynylation of carboxylic-phosphoric anhydrides via highly selective C(O)-O bond cleavage. Carboxylic-phosphoric anhydrides are highly active carboxylic acid derivatives, which are generated through activating carboxylic acids using phosphates by esterification or direct dehydrogenative coupling with phosphites. Highly valuable internal alkynes have been generated by the present method, and the efficiency of this approach has been demonstrated through a wide substrate scope and excellent functional group tolerance.

Photomediated Hydro(deutero)acylation of Olefins by Decarboxylative Addition of α-Oxocarboxylic Acids

Acyl radicals have been generated from the decarboxylation of α-oxocarboxylic acids by using a readily accessible organic pyrimidopteridine photoredox catalyst under ultraviolet-A (UV-A) light irradiation. These reactive acyl radicals were smoothly added to olefins such as styrenes and diverse Michael acceptors, with the assistance of H2O/D2O as hydrogen donors, enabling easy access to a diverse range of ketones/β-deuterio ketones. A wide range of α-oxocarboxylic acids are compatible with this reaction, which shows a reliable, atom-economical, and eco-friendly protocol. Furthermore, postsynthetic diversifications and applications are presented.

Electrochemical decarboxylative alkylation of β-ketoacids with phenol derivatives

An electrochemical method for the decarboxylative alkylation of β-ketoacids with phenol derivatives has been developed. The protocol was carried out in readily available unseparated cells at room temperature in the absence of catalysts and oxidants. The corresponding aryl ketones were obtained in satisfactory yields without additional electrolytes, and were easy to produce in gram-scale synthesis. Based on control experiments and cyclic voltammetry, a plausible reaction mechanism was proposed.

Merging Photocatalytic Doubly-Decarboxylative Csp 2 -Csp 2 Cross-Coupling for Stereo-Selective (E)-α,β-Unsaturated Ketones Synthesis

A photocatalytic domain of doubly decarboxylative Csp 2 -Csp 2 cross coupling reaction is disclosed. Merging iridium and palladium photocatalysis manifested carbon-carbon bonds in a tandem dual-radical pathway. Present catalytic platform efficiently cross-coupled α, β-unsaturated acids and α-keto acids to afford a variety of α, β-unsaturated ketones with excellent (E)-selectivity and functional group tolerance. Mechanistically, photocatalyst implicated through reductive quenching cycle whereas cross coupling proceeded over one electron oxidative pallado-cycle.

Recent Progress on the Synthesis of Bipyridine Derivatives

Bipyridine and related compounds are starting materials or precursors for a variety of valuable substances such as biologically active molecules, ligands for catalysts, photosensitizers, viologens, and supramolecular architectures. Thus, it is important to classify their synthesis methods and understand their characteristics. Representative examples include methods using homo and heterocoupling of pyridine derivatives in the presence of a catalyst. Because bipyridine compounds strongly coordinate with metal centers, a decrease in catalytic activity and yield is often observed in the reaction system. To address this issue, this review provides insights into advances over the last ~30 years in bipyridine synthesis using metal complexes under both homogeneous and heterogeneous conditions. Moreover, strategies for bipyridine synthesis involving sulfur and phosphorous compounds are examined. These alternative pathways offer promising avenues for overcoming the challenges associated with traditional catalysis methods, providing a more comprehensive understanding of the synthesis landscape.

RAFT Polymerisation by the Radical Decarboxylation of Carboxylic Acids

The controlled grafting of polymers from small- and macro-molecular substrates is an essential process for many advanced polymer applications. This usually requires the pre-functionalisation of substrates with an appropriate functional group, such as a RAFT agent or ATRP initiator, which requires additional synthetic steps. In this paper, we describe the direct grafting of RAFT polymers from carboxylate containing small molecules and polymers via photochemical radical decarboxylation. This method utilises the innate functional groups present in the substrates, and achieves efficient polymer initiation in a single step with excellent control of molecular weight and dispersity.

Switchable Decarboxylation by Energy- or Electron-Transfer Photocatalysis

Kolbe dimerization and Hofer-Moest reactions are well-investigated carboxylic acid transformations, wherein new carbon-carbon and carbon-heteroatom bonds are constructed via electrochemical decarboxylation. These transformations can be switched by choosing an electrode that allows control of the reactive intermediate, such as carbon radical or carbocation. However, the requirement of a high current density diminishes the functional group compatibility with these electrochemical reactions. Here, we demonstrate the photocatalytic decarboxylative transformation of activated carboxylic acids in a switchable and functional group-compatible manner. We discovered that switching between Kolbe-type or Hofer-Moest-type reactions can be accomplished with suitable photocatalysts by controlling the reaction pathways: energy transfer (EnT) and single-electron transfer (SET). The EnT pathway promoted by an organo-photocatalyst yielded 1,2-diarylethane from arylacetic acids, whereas the ruthenium photoredox catalyst allows the construction of an ester scaffold with two arylmethyl moieties via the SET pathway. The resulting radical intermediates were coupled to olefins to realize multicomponent reactions. Consequently, four different products were selectively obtained from a simple carboxylic acid. This discovery offers new opportunities for selectively synthesizing multiple products via switchable reactions using identical substrates with minimal cost and effort.

Catalytic π-π Interactions Triggered Photoinduced Synthesis of Biaryls

A highly regioselective photocatalytic method to access a variety of biaryl motifs under metal-free conditions has been developed. The organophotocatalyst is involved in π-π stacking interactions with the alkyne species, which promotes this photocatalytic process with thiophene. Mechanistic studies have shed light on these interactions and the overall process. Along with a broad functional-group tolerance and excellent regioselectivity, this protocol has been utilized in the late-stage functionalization of pharmaceuticals and other natural products.

Mild Pd-Catalyzed Decarboxylative Cross-Coupling of Zinc(II) Polyfluorobenzoates with Aryl Bromides and Nonaflates: Access to Polyfluorinated Biaryls

We developed a Pd-catalyzed decarboxylative cross-coupling of zinc polyfluorobenzoates, which were used as precursors for producing zinc reagents in situ, with aryl bromides and nonaflates, providing a mild and efficient pathway for the synthesis of polyfluorinated biaryls. This protocol exhibits a broad substrate scope and excellent functional tolerance. Moreover, the versatility of this approach was demonstrated by the straightforward late-stage modification of drugs, biologically active molecules, and pesticides, indicating its potential significance in drug discovery.

Decarboxylative Iodination and Suzuki-Miyaura Coupling Reactions to Access Chiral 3,3'-Diaryl-1,1'-bi-2-naphthols

An efficient synthesis of the enantiomerically pure 3,3'-bis-arylated BINOLs is accomplished through decarboxylative iodination of the dimethyl ether derivative of BINOL-3,3'-dicarboxylic acid followed by Suzuki-Miyaura coupling using a one-pot protocol. The decarboxylative iodination is effected with the dimethyl ether derivative of BINOL-3,3'-dicarboxylic acid using iodine as a terminal oxidant and the cheaply available K3PO4 as a base under neat conditions. This protocol facilitated the introduction of the aryl group at the 3,3'-position on the binaphthyl system using aryl boronic acid through a palladium-catalyzed Suzuki-Miyaura coupling reaction.

Synthetic Advantages of Defluorinative C-F Bond Functionalization

Much progress has been made in the development of methods to both create compounds that contain C-F bonds and to functionalize C-F bonds. As such, C-F bonds are becoming common and versatile synthetic functional handles. This review summarizes the advantages of defluorinative functionalization reactions for small molecule synthesis. The coverage is organized by the type of carbon framework the fluorine is attached to for mono- and polyfluorinated motifs. The main challenges, opportunities and advances of defluorinative functionalization are discussed for each class of organofluorine. Most of the text focuses on case studies that illustrate how defluorofunctionalization can improve routes to synthetic targets or how the properties of C-F bonds enable unique mechanisms and reactions. The broader goal is to showcase the opportunities for incorporating and exploiting C-F bonds in the design of synthetic routes, improvement of specific reactions and advent of new methods.

Base-Induced Decarboxylative 1,1-Alkoxy Thiolation via Hydrothiolation of Vinylene Carbonate

A base-mediated 1,1-difunctionalization of vinylene carbonate has been achieved using two different nucleophiles, namely, thiol and alcohol, with the assistance of air (O2). In alcoholic solvents, decarboxylation occurs at room temperature to provide a 1,1-difunctionalized product, where vinylene carbonate serves as an ethynol (C2) synthon in this three-component reaction. On the other hand, in acetonitrile, exclusive hydrothiolation occurs under the basic conditions at room temperature. This method offers a one-pot decarboxylative regioselective difunctionalization of vinylene carbonate at room temperature for the construction of α-alkoxy-β-hydroxy sulfide.

Synthesis of unsymmetrical ketones via dual catalysed cross-coupling of α,β-unsaturated carboxylic acids with aryldiazonium salts

A visible light-enabled synthesis of unsymmetrical ketones has been accomplished by the cross-coupling of α,β-unsaturated carboxylic acids and aryldiazonium salts embracing a synergistic eosin Y and Co(OAc)2·4H2O catalysis. The reaction involves decarboxylative aerobic CC bond cleavage, and is endowed with the creation of new C-C and C-O bonds with good substrate scope.

Visible-Light Mediated Deoxygenation of Carboxylic Acid for Late-Stage Peptide Modification Targeting Dehydroalanine

A visible-light mediated deoxygenative radical addition of carboxylic acids to dehydroalanines has been disclosed. The method can be used in β-acyl alanine derivative synthesis, including those chiral and deuterated variants, and late-stage peptide modification with various functional groups, both in the homogeneous phase and on the resin in SPPS. It provides a new tool kit for rapid construction of bioactive peptide analogues, which has been demonstrated by modification of the antimicrobial peptide Feleucin-K3.

Transition-Metal-Catalyzed C-C Bond Formation from C-C Activation

ConspectusC-C single bonds are ubiquitous in organic compounds. The activation and subsequent functionalization of C-C single bonds provide a unique opportunity to synthesize conventionally inaccessible molecules through the rearrangement of carbon skeletons, often with a favorable atom and step economy. However, the C-C bonds are thermodynamically and kinetically inert. Consequently, the activation of C-C bonds is particularly attractive yet challenging in the field of organic chemistry. In the past decade, we sought to develop efficient strategies to carry out transition-metal-catalyzed diverse C-C cleavage/C-C forming reactions and to obtain some insights into the intrinsic reactivities of different C-C bonds. With our efforts, readily available alcohols, carboxylic acids, and ketones served as suitable substrates for the catalytic C-C coupling reactions, which are reviewed in this Account. In 2009, we observed a Ni-catalyzed cross coupling of aryl nitriles with arylboronic esters through C-CN cleavage. Encouraged by these results, we are interested in transition-metal-catalyzed C-C bond activation. Due to their broad availability, we then turned our attention to C-C cleavage of carboxylic acids. Rhodium-catalyzed decarbonylative coupling of carboxylic acids with (hetero)arenes was then achieved through oxidative addition of in situ formed, more reactive mixed anhydrides to Rh(I) without the need for oxidants that are commonly required for the decarboxylative coupling of carboxylic acids. Subsequently, the decarbonylation of more challenging unstrained aryl ketones was realized under Rh catalysis assisted by N-containing directing groups. Following this work, a group exchange of aryl ketones with carboxylic acids was achieved through 2-fold C-C bond cleavage. By employing the chelation strategy, Rh-catalyzed C-C bond activation of secondary benzyl alcohols was also accomplished through β-carbon elimination of the rhodium alcoholate intermediates. The competing oxidation of secondary alcohols to ketones via β-hydrogen elimination of the same intermediates was suppressed as thermodynamically favorable five-membered rhodacycles are formed after β-carbon elimination. Different types of transformations of alcohols, including the Heck-type reaction with alkenes, cross coupling with arylsilanes, and Grignard-type addition with aldehydes or imines, have been achieved, showing the great potential of secondary alcohols in the formation of C-C bonds. These C-C bond-forming reactions are complementary to traditional cross couplings of aryl halides with organometallic reagents. However, these transformations produce small molecules as byproducts. To improve the atom economy, we then investigated C-C bond transformations of strained-ring cyclic compounds. Ni-catalyzed intermolecular cyclization of benzocyclobutenones with alkynes was recently achieved via the uncommon cleavage of the C1-C8 bond by employing a removable blocking strategy. Rh-catalyzed intramolecular annulation of benzocyclobutenols with alkynes was also achieved. In summary, our developments demonstrate the great potential of transition-metal-catalyzed C-C bond activation for the formation of new C-C bonds. To further expand the synthetic utility of C-C bond activation, more efforts are required to expand the substrate scope and to achieve earth-abundant metal-catalyzed transformations.

Diastereoselective Hydroacylation of Cyclopropenes by Visible-Light Photocatalysis

An efficient and general strategy for the hydroacylation of cyclopropene is disclosed for synthesizing various 2-acylcyclopropane derivatives under mild reaction conditions. High functional group tolerance of this protocol features a novel route to access a divergent synthesis of acylated cyclopropane in a diastereoselective manner by photoinduced decarboxylation of α-ketoacid followed by acyl radical addition to cyclopropene. Additionally, the regioselective addition of acyl radical at the least substituted olefinic carbon center with trans-selective fashion makes this protocol more appealing toward natural product development.

Rearrangement of a carboxy-substituted spiro[4.4]nonatriene to annulated fulvenes through a Pd(ii)-mediated 1,5-vinyl shift

A novel synthesis of aryl-substituted, enantioenriched fulvenes from an oxidative Heck cascade and rearrangement of a carboxy-substituted spiro[4.4]nonatriene is disclosed. Mechanistic investigations with density functional theory (DFT) calculations and empirical results support the net transformation occurring through a novel Pd(ii)-mediated 1,5-vinyl shift from a vinyl-palladium intermediate that terminates with protodepalladation. This spiro-to-fused bicycle conversion tolerates a range of electron-rich and deficient arylboronic acids to give a range of mono- and diaryl substituted annulated fulvenes in moderate to good yields and enantiomeric ratios. Overall, this work connects two classes of molecules with a rich history in physical organic chemistry.

Pd-Catalyzed Activation of Carbon-Carbon Bonds in Hydroxymethylfurfural Derivatives

Palladium-catalyzed activation of C-C bonds in organic molecules is a powerful tool for the synthesis of value-added compounds. 5-Hydroxymethylfurfural (HMF) derivatives are a promising class of biomass-derived chemicals that have received considerable attention due to their potential applications in the synthesis of biologically active molecules and materials. However, the selective activation of unstrained C-C bonds is a challenging task, mainly due to their relatively high bond dissociation energies. Herein, we report a palladium-catalyzed method for the efficient C-C bond activation of HMF derivatives, enabling their arylation with iodobenzenes. Mechanistic studies, including reaction-profile analysis, competition experiments and head-space IR spectroscopy suggest a decarboxylative mechanism.

Regioselective Decarboxylative Transformations of Tetrahydro-β-carboline-1-carboxylic Acid: Reagent Controlled Selectivity toward Alkynylated or Enaminone Products

A one-pot, regioselective decarboxylative alkynylation of tetrahydro-β-carboline-1-carboxylic acid under peroxide-free condition is reported. The reaction is highly selective for the 1-position over the 3-position of tetrahydro-β-carboline. The reaction can afford alkynylated or enaminone products depending on the reagent. The reaction proceeds through sequential decarboxylative iminium ion formation followed by an alkynylation and oxidative rearrangement cascade.

Decarboxylative N-Formylation of Amines with Glyoxylic Acid Promoted by H2O2

A novel method for the synthesis of formamides through the decarboxylative N-formylation of amines with glyoxylic acid has been developed. This transformation provides an efficient protocol for the synthesis of various formamides with moderate to excellent yields, and it can accommodate a wide range of functional groups under metal free and base free conditions. In addition, the large-scale experiments and high chemoselectivity have shown great potential application of this strategy.

Nickel-Catalyzed Asymmetric Decarboxyarylation with NHP Esters of α-Amino Acid to Chiral Benzylamines

A nickel-catalyzed asymmetric decarboxyarylation of NHP esters via reductive cross-coupling has been established. Utilizing the NHP of amino acid esters as radical precursors furnishes a new protocol in which structurally diverse chiral benzylamines could be accessible. This method has demonstrated excellent catalytic efficiency, high enantioselective control, mild conditions, and good functional group tolerance, thus enabling the late-stage modification of bioactive molecules and pharmaceuticals.

Photocatalytic Decarboxylative Minisci Reaction Catalyzed by Palladium-Loaded Gallium Nitride

The decarboxylative Minisci reaction is a versatile tool for the direct C-H alkylation of heteroarenes, where stoichiometric amounts of oxidants or expensive, precious metal reagents are commonly used. Herein, we reported a photodriven decarboxylative Minisci reaction enabled by a gallium nitride-based heterogeneous photocatalyst under mild conditions. This method can be effectively applied to a broad substrate scope of acids, including primary, secondary, and tertiary carboxylic acids and N-heteroarenes effectively. The practicability and robustness of the approach are demonstrated for the functionalization of biologically active compounds.

Effects of phosphine ligands in nickel-catalyzed decarbonylation reactions of lactone

Due to the ubiquity of carbonyl compounds and the abundance of nickel on the earth, nickel-catalyzed decarbonylation has garnered increasing attention in recent years. This type of reaction has seen significant developments in various aspects; however, certain challenges concerning reactivity, selectivity, and transformation efficiency remain pressing and demand urgent resolution. In this study, we employed DFT calculations to investigate the mechanism of nickel-catalyzed decarbonylation reactions involving lactones, as well as the effects of phosphine ligands. Mechanically, Ni(0) first activates the C(acyl)-O bond of the lactone, followed by a decarbonylation step, and ultimately results in reductive elimination under carbonyl coordination to yield the product. Through a comprehensive examination of the electronic and steric effects of the phosphine ligands, we deduced that the electronic effect of the ligand plays a dominant role in the decarbonylation reaction. By enhancing the electron-withdrawing ability of the ligand, the energy barrier of the entire reaction can be significantly reduced. The obtained insights should be valuable for understanding the detailed mechanism and the role of phosphine ligands in nickel catalysis. Moreover, they offer crucial clues for the rational design of more efficient catalytic reactions.

Modern Strategies for Carbon Isotope Exchange

In contrast to stable and natural abundant carbon-12, the synthesis of organic molecules with carbon (radio)isotopes must be conceived and optimized in order to navigate through the hurdles of radiochemical requirements, such as high costs of the starting materials, harsh conditions and radioactive waste generation. In addition, it must initiate from the small cohort of available C-labeled building blocks. For long time, multi-step approaches have represented the sole available patterns. On the other side, the development of chemical reactions based on the reversible cleavage of C-C bonds might offer new opportunities and reshape retrosynthetic analysis in radiosynthesis. This review aims to provide a short survey on the recently emerged carbon isotope exchange technologies that provide effective opportunity for late-stage labeling. At present, such strategies have relied on the use of primary and easily accessible radiolabeled C1-building blocks, such as carbon dioxide, carbon monoxide and cyanides, while the activation principles have been based on thermal, photocatalytic, metal-catalyzed and biocatalytic processes.

Recent Developments on Photochemical Synthesis of 1,n-Dicarbonyls

1,n-dicarbonyls are one of the most fascinating chemical feedstocks finding abundant usage in the field of pharmaceuticals. Besides, they are utilized in a plethora of synthesis in general synthetic organic chemistry. A number of 'conventional' methods are available for their synthesis, such as the Stetter reaction, Baker-Venkatraman rearrangement, oxidation of vicinal diols, and oxidation of deoxybenzoins, synonymous with unfriendly reagents and conditions. In the last 15 years or so, photocatalysis has taken the world of synthetic organic chemistry by a remarkable renaissance. It is fair to say now that everybody loves the light and photoredox chemistry has opened a new gateway to organic chemists towards milder, more simpler alternatives to the previously available methods, allowing access to many sensitive reactions and products. In this review, we present the readers with the photochemical synthesis of a variety of 1,n-dicarbonyls. Diverse photocatalytic pathways to these fascinating molecules have been discussed, placing special emphasis on the mechanisms, giving the reader an opportunity to find all these significant developments in one place.

Cationic Iridium-Catalyzed Decarboxylation of Aromatic Carboxylic Acids

Practical synthetic applications of catalytic decarboxylation in producing useful molecules are limited. We report herein the cationic Ir-catalyzed decarboxylations of various electron-rich and -poor aromatic carboxylic acids to produce hydrocarbons in good yield (up to >99%). Additionally, this reaction is applicable in decarboxylative hydroarylation of bicyclic alkenes and decarboxylative fluorination, indicating the potential utility of this catalytic decarboxylation in synthetic chemistry.

Palladium-Catalyzed Decarbonylative Annulation of 2-Arylbenzoic Acids with Internal Alkynes toward Phenanthrenes

A palladium-catalyzed decarbonylative annulation of 2-arylbenzoic acids with internal alkynes via C(sp2)-H activation has been developed. A series of phenanthrenes were produced in moderate to good yield with good functional group tolerance. The mechanism study indicated that the C(sp2)-H activation should be the rate-determining step during the reaction.

Enantioselective catalytic radical decarbonylative azidation and cyanation of aldehydes

Empowered by the ubiquity of carbonyl functional groups in organic compounds, decarbonylative functionalization was prevalent in the construction of complex molecules. Under this context, asymmetric decarbonylative functionalization has emerged as an efficient pathway to accessing chiral motifs. However, ablation of enantiomeric control in a conventional 2e transition metal-catalyzed process was notable because of harsh conditions (high temperatures, etc.) that are usually required. To address this challenge and use readily accessible aldehyde directly, we report the asymmetric radical decarbonylative azidation and cyanation. Diverse aldehydes were directly used as alkyl radical precursor, engaging in the subsequent inner-sphere or outer-sphere ligand transfer where functional motifs (CN and N3) could be incorporated in excellent site- and enantioselectivity. Mild conditions, broad scope, excellent regioselectivity (driven by polarity-matching strategy), and enantioselectivity were shown for both transformations. This radical decarbonylative strategy using aldehydes as alkyl radical precursor has offered a powerful reaction manifold in asymmetric radical transformations to construct functional motifs regio- and stereoselectively.

Esterification of Thioamides via Selective N-C(S) Cleavage under Mild Conditions

Herein, we report an exceedingly mild method for the direct, transition-metal-free esterification of thioamides through the selective generation of tetrahedral intermediates. The method represents the first transition-metal-free approach to the thioamide to thionoester transformation in organic synthesis. This reactivity has been accomplished through N,N-Boc2-thioamides that engage in ground-state destabilization of the nN → π*C═S conjugation. The ground-state destabilization of "single-atom" bioisosteric thioamides will expand the arsenal of valuable amide bond functionalization reactions.

Selective synthesis of meta-phenols from bio-benzoic acids via regulating the adsorption state

Phenols are important building blocks widely applied in many fields. The pronounced orientational effect of the phenolic hydroxyl group makes achieving selective synthesis of meta-phenols challenging. Accessing meta-phenols needs lengthy synthetic sequences. Herein, we first developed a heterogeneous CO2-mediated CeO2-5CuO catalyst for decarboxylative oxidation of benzoic acids with a more than 80% selectivity to meta-phenols. This technology is based on a traceless directing group relay method. The CeO2-CuO catalysts with different Ce/Cu ratios exhibited controllable reaction selectivity between decarboxylation and decarboxylative oxidation. Spectroscopy experiments and computational studies showed the adsorption state of benzoic acid was found to be crucial for subsequent reaction pathways. The moderate adsorption on CO2-mediated CeO2-5CuO catalyst contributes to the distinct selectivity of phenol. Furthermore, the paddlewheel intermediate facilitates the synthesis of meta-phenols from benzoic acids. This traceless directing group method would promote the development of useful one-pot meta-substituted phenols from bio-based benzoic acids.

Translating Planar Heterocycles into Three-Dimensional Analogs by Photoinduced Hydrocarboxylation

The rapid preparation of complex three-dimensional (3D) heterocyclic scaffolds is a key challenge in modern medicinal chemistry. Despite the increased probability of clinical success for small molecule therapeutic candidates with increased 3D complexity, new drug targets remain dominated by flat molecules due to the abundance of coupling reactions available for their construction. In principle, heteroarene hydrofunctionalization reactions offer an opportunity to transform readily accessible planar molecules into more three-dimensionally complex analogs through the introduction of a single molecular vector. Unfortunately, dearomative hydrofunctionalization reactions remain limited. Herein, we report a new strategy to enable the dearomative hydrocarboxylation of indoles and related heterocycles. This reaction represents a rare example of a heteroarene hydrofunctionalization that meets the numerous requirements for broad implementation in drug discovery. The transformation is highly chemoselective, broad in scope, operationally simple, and readily amenable to high-throughput experimentation (HTE). Accordingly, this process will allow existing libraries of heteroaromatic compounds to be translated into diverse 3D analogs and enable exploration of new classes of medicinally relevant molecules.

Skeletal Editing of Dibenzolactones to Fluorenes via Ni- or Pd-Catalyzed Decarboxylation

The skeletal editing of dibenzolactones to fluorenes by Ni- or Pd-catalyzed decarboxylation is reported. In contrast to previously reported intramolecular decarboxylative couplings, inductively electron-withdrawing ortho substituents on the aryl carboxylate moiety and metal additives are not required. The decarboxylation reaction proceeds cleanly and can be applied to the skeletal editing of a natural product analogue. Mechanistic observations are consistent with stabilization of the carboxylate-ligated Ni complex over the Ni-carboxylate ion pair, which is the key factor in promoting the challenging decarboxylation step in the catalytic cycle.

Silver-Catalyzed Decarboxylative Acylation of Isocyanides Accesses to α-Ketoamides with Air as a Sole Oxidant

α-Ketoamide moieties, as privileged units, may represent a valuable option to develop compounds with favorable biological activities, such as low toxicity, promising PK and drug-like properties. An efficient silver-catalyzed decarboxylative acylation of α-oxocarboxylic acids with isocyanides was developed to derivatize the α-ketoamide functional group via a multicomponent reaction (MCR) cascade sequence in one pot. A series of α-ketoamides was synthesized with three components of isocyanides, aromatic α-oxocarboxylic acid analogues and water in moderate yields. Based on the research, the silver-catalyzed decarboxylative acylation confirmed that an oxygen atom of the amide moiety was derived from the water and air as a sole oxidant for the whole process.

Copper-Catalyzed Asymmetric Cyanation of Propargylic Radicals via Direct Decarboxylation of Propargylic Carboxylic Acids

Chiral propargylic cyanides are often used as small-molecule feedstocks for the introduction of chiral centers into various valuable products and complex molecules. Here, we have developed a highly atom-economical strategy for the chiral copper complex-catalyzed synthesis of chiral propargylic cyanides. Propargylic radicals can be smoothly obtained by direct decarboxylation of the propargylic carboxylic acids without preactivation. The reactions show excellent selectivity and functional group compatibility. Gram-scale reaction and several conversion reactions from chiral propargylic cyanide have demonstrated the synthetic value of this strategy.