Carbonylative Coupling of Alkyl Zinc Reagents with Benzyl Bromides Catalyzed by a Nickel/NN2 Pincer Ligand Complex

Electrochemical Synergistic Ni/Co-Catalyzed Carbonylative Cross-Electrophile Coupling of Aryl and Alkyl Halides with CO

Accessing unsymmetric ketones and achieving their carbon isotope labeling are crucial yet challenging tasks in both synthetic and medicinal chemistry. We report here an efficient electrochemical nickel-/cobalt-catalyzed carbonylative cross-electrophile coupling reaction. This method allows for the modular synthesis of a library of unsymmetric ketones from simple building blocks, including aryl halides, alkyl halides, and gaseous CO. The simultaneous use of nickel and cobalt salts as concerted catalysts ensures the high efficiency of this three-component carbonylative coupling. Furthermore, electrochemical reduction avoids the use of stoichiometric reductants, making this protocol more sustainable and attractive. The broad substrate scope and late-stage 13C isotope labeling of complex molecules derived from biologically active compounds highlight the practicality of this method.

A General Access to Aryl-Alkyl Ketones via Nickel-Catalyzed Carbonylative Reductive Cross-Coupling Reactions

Transition-metal-catalyzed carbonylation reactions have emerged as a versatile and powerful strategy for the production of diverse value-added carbonyl-containing compounds. Nevertheless, the carbonylative synthesis of alkyl ketones, particularly those incorporating secondary or tertiary alkyl fragments, remains underexplored and poses significant challenges. Herein, we present a nickel-catalyzed carbonylative reductive cross-coupling reaction to synthesize a wide range of aryl-alkyl ketones from readily available alkyl halides, aryl iodides, and Mo(CO)6. This protocol exhibits excellent compatibility with primary, secondary, and tertiary alkyl electrophiles as well as aryl electrophiles bearing electron-withdrawing or electron-donating groups, offering a general access to aryl-alkyl ketones under mild conditions. Mechanistic studies reveal that Mo(CO)6 not only serves as a safe and effective CO surrogate, but also plays a crucial role in facilitating the nickel carbonyl species, which is critical for promoting the selective synthesis of aryl-alkyl ketones.

Nickel Catalyzed Carbonylative Cross Coupling for Direct Access to Isotopically Labeled Alkyl Aryl Ketones

Here we present an effective nickel-catalyzed carbonylative cross-coupling for direct access to alkyl aryl ketones from readily accessible redox-activated tetrachlorophthalimide esters and aryl boronic acids. The methodology, which is run employing only 2.5 equivalents of CO and simple Ni(II) salts as the metal source, exhibits a broad substrate scope under mild conditions. Furthermore, this carbonylation chemistry provides an easy switch between isotopologues for stable (13CO) and radioactive (14CO) isotope labeling, allowing its adaptation to the late-stage isotope labeling of pharmaceutically relevant compounds. Based on DFT calculations as well as experimental evidence, a catalytic cycle is proposed involving a carbon-centered radical formed via nickel(I)-induced outer-sphere decarboxylative fragmentation of the redox-active ester.

Carbonylation Reactions at Carbon-Centered Radicals with an Adjacent Heteroatom

Heteroatoms are essential to living organisms and present in almost all molecules with medicinal usage. The catalytic functionalization at the carbon-centered radical with an adjacent heteroatom provides an effective way to value added moiety while retaining the unique physicochemical and pharmacological properties of heteroatoms, which can promote the development of pharmaceutical and fine chemical production. Carbonylative transformation was discovered nearly a century ago which is an efficient method for the synthesis of carbonyl-containing molecules with potent applications in both industry and academia. Despite numerous advances in new reaction development, carbonylative transformation involving adjacent heteroatom carbon radical remain a subject that deserves to be discussed. In this minireview, we systematically summarized and discussed the recent advances in carbonylative transformations involving carbon-centered radicals with an adjacent heteroatom, including oxygen (O), nitrogen (N), phosphorus (P), silicon (Si), sulfur (S), boron (B), fluorine (F), and chlorine (Cl). The related reaction mechanism was also discussed.

Nickel-Catalyzed Carbonylative Negishi Cross-Coupling of Unactivated Secondary Alkyl Electrophiles with 1 atm CO Gas

We describe a nickel-catalyzed carbonylative cross-coupling of unactivated secondary alkyl electrophiles with the organozinc reagent at atmospheric CO gas, thus allowing the expedient construction of unsymmetric dialkyl ketones with broad functional group tolerance. The leverage of a newly developed NN2-pincer type ligand enables the chemoselective three-component carbonylation by overcoming the competing Negishi coupling, the undesired β-hydride elimination, and dehalogenation of alkyl iodides side pathways. Both alkyl iodides and alkyl tosylates are compatible in the single electron transfer involved mechanism.

Functional-Group-Tolerant Pd-Catalyzed Carbonylative Negishi Coupling with Aryl Iodides

A chemoselective Pd-mediated carbonylative Negishi-type catalytic protocol for the synthesis of (hetero)aryl ketones is reported. The protocol employs the PEPPSI-IPr precatalyst and CO gas at atmospheric pressure (balloon) to foster the carbonylative coupling between diverse C(sp3)-hybridized organozinc reagents and a broad range of aryl iodides, including substrates carrying aldehyde, aniline, phenol, or carboxylic acid groups, and heteroaryls.

Nickel-Catalyzed Enantioselective Hydrothiocarbonylation of Cyclopropenes

Hydrothiocarbonylation of olefins using carbon monoxide and thiols is a powerful method to synthesize thioesters from simple building blocks. Owing to the intrinsic challenges of catalyst poisoning, transition-metal-catalyzed asymmetric thiocarbonylation, particularly when utilizing earth abundant metals, remains rare in the literature. Herein, we report a nickel-catalyzed enantioselective hydrothiocarbonylation of cyclopropenes for the synthesis of a diverse collection of functionalized thioesters in good to excellent yields with high stereoselectivity. This new method employs an inexpensive, air-stable nickel(II) precursor, which provides enhanced catalyst fidelity against CO poisoning compared to nickel(0) catalysts.

Deciphering the Mechanism of MRSA Targeting Copper(II) Complexes of NN2 Pincer-Type Ligands

WHO lists AMR as one of the top ten global public health issues. Therefore, constant effort is needed to develop more efficient antimicrobial drugs. As a result, earth-abundant transition-metal complexes have emerged as an excellent solution. In this regard, new aminoquinoline-based copper(II) pincer complexes 1-3 were designed, synthesized, and characterized by modern spectroscopic techniques. It is worth mentioning that, at the highest concentration (1024 μg/mL) of complexes (1-3), the hemolysis was found to be <15%, implying their less toxicity. Further, the complexes effectively interfered with the growth of Gram positive MRSA and the fungus Candida albicans. Among them, complex 2 was promising (MIC = 16 μg/mL) against MRSA, which was better than the known antibacterial drug kanamycin (64 μg/mL) under identical conditions. The Alamar blue cell viability test and the MBC/MFC identified by spot assay were in accordance with MIC values. Moreover, the insilico studies explained the most probable mechanism of action as inhibition of cell wall biosynthesis and dysfunction of antibiotic sensing proteins. Similarly, the antifungal action might be due to the cell surface adhesion protein dysfunction by the complexes. Furthermore, we are expecting to draw these compounds for clinical applications.

Nickel-catalyzed acylzincation of allenes with organozincs and CO

Transition metal-catalyzed carbonylative reaction with CO gas are among the central task in organic synthesis, enabling the construction of highly valuable carbonyl compound. Here, we show an earth-abundant nickel-catalyzed three-component tandem acylzincation/cyclization sequence of allene and alkylzinc reagent with 1 atm of CO under mild conditions. This protocol is featured by broad functional group tolerance with high reaction selectivity, providing a rapid and convenient synthetic method for the construction of diverse fully substituted benzotropone derivatives. Mechanistic studies reveal that the installation of a cyano group tethered to allene moiety enables the high regio- and stereoselectivity of this acylzincation of allene, allowing the selective formation of three consecutive C-C bonds in a highly efficient manner.

Are Zn(II) pincer complexes efficient apoptosis inducers? a deep insight into their activity against A549 lung cancer cells

To expand the array of chemotherapeutic drugs, earth-abundant metal complexes are found to be the future direction. In this regard, new zinc(II) complexes 1-3 of 8-aminoquinoline-based pincer ligands were synthesized, characterized and tested for their anticancer activity. The IC50 values of these complexes were estimated by an MTT assay to be 16.35-17.95 μM and 33.35-40 μM against A549 lung and MCF-7 breast cancer cells respectively. Among them, 3 was slightly better than the other complexes and, thus, subjected to detailed studies. Moreover, the ligand corresponding to 3 was less active against both the cell lines than the complex. Further, 3 showed no toxicity against normal fibroblast cell line L929, which instantly elevated the drug characteristic of our complex. An AO-EB staining assay revealed that 3 can induce apoptosis in A549, and it was quantified by flow cytometry as 22.77%. Moreover, the depolarization of the mitochondrial membrane potential determined by JC-1 staining indicated excess ROS production sites in the mitochondria, which was confirmed by carboxy-H2DCFDA staining. Interestingly, the present complexes show better activity than that of the standard drug cisplatin against A549 cells. Overall, the studies provided promising results that can be extended for clinical applications.

Mono and Dinuclear Palladium Pincer Complexes of NNSe Ligand as a Catalyst for Decarboxylative Direct C-H Heteroarylation of (Hetero)arenes

This report describes the synthesis of a new NNSe pincer ligand and its mono- and dinuclear palladium(II) pincer complexes. In the absence of a base, a dinuclear palladium pincer complex (C1) was isolated, while in the presence of Et3 N base a mononuclear palladium pincer complex (C2) was obtained. The new ligand and complexes were characterized using techniques like 1 H, 13 C{1 H} nuclear magnetic resonance (NMR), fourier transform infrared (FTIR), high-resolution mass spectrometry (HRMS), ultraviolet-visible (UV-Visible), and cyclic voltammetry. Both the complexes showed pincer coordination mode with a distorted square planar geometry. The complex C1 has two pincer ligands attached through a Pd-Pd bond in a dinuclear pincer fashion. The air and moisture-insensitive, thermally robust palladium pincer complexes were used as the catalyst for decarboxylative direct C-H heteroarylation of (hetero)arenes. Among the complexes, dinuclear pincer complex C1 showed better catalytic activity. A variety of (hetero)arenes were successfully activated (43-87 % yield) using only 2.5 mol % of catalyst loading under mild reaction conditions. The PPh3 and Hg poisoning experiments suggested a homogeneous nature of catalysis. A plausible reaction pathway was proposed for the dinuclear palladium pincer complex catalyzed decarboxylative C-H bond activation reaction of (hetero)arenes.

Palladium-Catalyzed Carbonylative Difunctionalization of Unactivated Alkenes Initiated by Unstabilized Enolates

This report describes the first example of palladium-catalyzed carbonylative difunctionalization of unactivated alkenes initiated by enolate nucleophiles. The approach involves initiation by an unstabilized enolate nucleophile under an atmospheric pressure of CO and termination with a carbon electrophile. This process is compatible with a diverse range of electrophiles, including aryl, heteroaryl, and vinyl iodides to yield synthetically useful 1,5-diketone products, which were demonstrated to be precursors for multi-substituted pyridines. A PdI -dimer complex with two bridging CO units was observed although its role in catalysis is not yet understood.

A Visible Light Driven Nickel Carbonylation Catalyst: The Synthesis of Acid Chlorides from Alkyl Halides

We describe here the development of a visible light driven nickel carbonylation catalyst. The combination of the large bite-angle Xantphos ligand with nickel(0) generates a catalyst capable of activating alkyl halides toward carbonylation at ambient temperature in the presence of blue light irradiation, and the reductive elimination of high energy acid chloride products. Unlike classical carbonylations, where the coordination of carbon monoxide inhibits the reactivity of earth abundant nickel catalysts, a CO-associated nickel is found to be the active catalyst in the reaction. Coupling the build-up of acid chlorides with nucleophile addition can be used to access various amides, esters and thioesters, including those of sterically encumbered substrates or with metal-reactive functionalities.

Nickel-Catalyzed Aminocarbonylation of Aryl Iodides with 1 atm CO

Reported here is a nickel-catalyzed aminocarbonylation of aromatic iodides with (hetero)aryl anilines and alkyl amines under atmospheric CO pressure. The reaction features with broad substrate scope with excellent functional group tolerance, providing an expedient method for the construction of amide analogues. Notably, amino alcohols can be selectively transformed into the corresponding amides successfully without interfering the hydroxyl group under the current standard conditions.

Oxidative C-H/N-H Carbonylation of Benzamide by Nickel Catalysis with CO as the Carbonyl Source

An efficient and direct carbonylation of aminoquinoline benzamides has been developed using abundant and inexpensive Ni(OAc)₂·4H₂O as the catalyst and carbon monoxide as a cost-efficient C1 building block. This process features good functional-group tolerance and can be conducted on gram scale. The directing group can be easily removed under mild conditions.

Late-Stage Carbon-14 Labeling and Isotope Exchange: Emerging Opportunities and Future Challenges

Carbon-14 (¹⁴C) is a gold standard technology routinely utilized in pharmaceutical and agrochemical industries for tracking synthetic organic molecules and providing their metabolic and safety profiles. While the state of the art has been dominated for decades by traditional multistep synthetic approaches, the recent emergence of late-stage carbon isotope labeling has provided new avenues to rapidly access carbon-14-labeled biologically relevant compounds. In particular, the development of carbon isotope exchange has represented a fundamental paradigm change, opening the way to unexplored synthetic transformations. In this Perspective, we discuss the recent developments in the field with a critical assessment of the literature. We subsequently discuss research directions and future challenges within this rapidly evolving field.

Nickel-Catalyzed Carbonylative Synthesis of α,β-Unsaturated Thioesters from Vinyl Triflates and Arylsulfonyl Chlorides

A straightforward and efficient synthesis of α,β-unsaturated thioesters has been developed via a nickel-catalyzed thiocarbonylation reaction of vinyl triflates with arylsulfonyl chlorides. With Mo(CO)₆ as both CO source and reductant, a variety of α,β-unsaturated thioesters were obtained in moderate to good yields with very good functional group compatibility. It is noteworthy that the present method is the first example on nickel-catalyzed carbonylative synthesis of α,β-unsaturated thioesters by using arylsulfonyl chlorides as the coupling partner.

Nickel-catalyzed alkoxycarbonylation of aryl iodides with 1 atm CO

A nickel-catalyzed alkoxycarbonylation of aromatic iodides with alcohols under atmospheric pressure of carbon monoxide is presented here. This operationally simple protocol allows the facile synthesis of (hetero)aromatic esters, exhibiting broad substrate scope with excellent functional group tolerance. Various primary and secondary aliphatic alcohols as well as phenols are suitable for this transformation.

Nickel-Catalyzed Carbonylation of Cyclopropanol with Benzyl Bromide for Multisubstituted Cyclopentenone Synthesis

Herein, we reported a Ni-catalyzed carbonylation of cyclopropanol with benzyl bromide to afford multisubstituted cyclopentenone under 1 atm of CO. The reaction proceeds through cascade carbonylation of benzyl bromides, followed by generation of nickel homoenolate from cyclopropanols via β-C elimination to afford 1,4-diketones, which undergoes intramolecular Aldol condensation to furnish highly substituted cyclopentenone derivatives in moderate to good yields. The reaction exhibits high functional group tolerance with broad substrate scope.

Ruthenium pincer complex-catalyzed heterocycle compatible alkoxycarbonylation of alkyl iodides: substrate keeps the catalyst active

The electron pair of the heteroatom in heterocycles will coordinate with metal catalysts and decrease or even inhibit their catalytic activity consequently. In this work, a pincer ruthenium-catalyzed heterocycle compatible alkoxycarbonylation of alkyl iodides has been developed. Benefitting from the pincer ligand, a variety of heterocycles, such as thiophenes, morpholine, unprotected indoles, pyrrole, pyridine, pyrimidine, furan, thiazole, pyrazole, benzothiadiazole, and triazole, are compatible here.

Nickel-catalyzed carbonylative domino cyclization of arylboronic acid pinacol esters with 2-alkynyl nitroarenes toward N-aroyl indoles

A nickel-catalyzed carbonylative domino cyclization of arylboronic acid pinacol esters with 2-alkynyl nitroarenes has been developed.

Regioselective Hydroalkylation of Vinylarenes by Cooperative Cu and Ni Catalysis

Disclosed here is a dual copper and nickel catalytic system with a silyl hydride source for promoting the linear selective hydroalkylation of vinylarenes. This carbon-carbon bond-forming protocol is applied to couple a variety of functionalized vinylarenes with alkyl halides applying a nickel(II) NNN pincer complex in the presence of an NHC-ligated copper catalyst. This combination allows for a 1 mol % loading of the nickel catalyst leading to turnover numbers of up to 72. Over 40 examples are presented, including applications for pharmaceutical diversification. Labeling experiments demonstrated the regioselectivity of the reaction and revealed that the copper catalyst plays a crucial role in enhancing the rate for formation of the reactive linear alkyl nickel complex. Overall, the presented work provides a complimentary approach for hydroalkylation reactions, whilst providing a preliminary mechanistic understanding of the cooperativity between the copper and nickel complexes.

Nickel-Mediated Alkoxycarbonylation for Complete Carbon Isotope Replacement

Many commercial drugs, as well as upcoming pharmaceutically active compounds in the pipeline, display aliphatic carboxylic acids or derivatives thereof as key structural entities. Synthetic methods for rapidly accessing isotopologues of such compounds are highly relevant for undertaking critical pharmacological studies. In this paper, we disclose a direct synthetic route allowing for full carbon isotope replacement via a nickel-mediated alkoxycarbonylation. Employing a nickel^II pincer complex ([(N₂N)Ni-Cl]) in combination with carbon-13 labeled CO, alkyl iodide, sodium methoxide, photocatalyst, and blue LED light, it was possible to generate the corresponding isotopically labeled aliphatic carboxylates in good yields. Furthermore, the developed methodology was applied to the carbon isotope substitution of several pharmaceutically active compounds, whereby complete carbon-13 labeling was successfully accomplished. It was initially proposed that the carboxylation step would proceed via the in situ formation of a nickellacarboxylate, generated by CO insertion into the Ni-alkoxide bond. However, preliminary mechanistic investigations suggest an alternative pathway involving attack of an open shell species generated from the alkyl halide to a metal ligated CO to generate an acyl Ni^III species. Subsequent reductive elimination involving the alkoxide eventually leads to carboxylate formation. An excess of the alkoxide was essential for obtaining a high yield of the product. In general, the presented methodology provides a simple and convenient setup for the synthesis and carbon isotope labeling of aliphatic carboxylates, while providing new insights about the reactivity of the N₂N nickel pincer complex applied.

Nickel-Catalyzed Multicomponent Coupling: Synthesis of α-Chiral Ketones by Reductive Hydrocarbonylation of Alkenes

A nickel-catalyzed, multicomponent regio- and enantioselective coupling via sequential hydroformylation and carbonylation from readily available starting materials has been developed. This modular multicomponent hydrofunctionalization strategy enables the straightforward reductive hydrocarbonylation of a broad range of unactivated alkenes to produce a wide variety of unsymmetrical dialkyl ketones bearing a functionalized α-stereocenter, including enantioenriched chiral α-aryl ketones and α-amino ketones. It uses chiral bisoxazoline as a ligand, silane as a reductant, chloroformate as a safe CO source, and a racemic secondary benzyl chloride or an N-hydroxyphthalimide (NHP) ester of a protected α-amino acid as the alkylation reagent. The benign nature of this process renders this method suitable for late-stage functionalization of complex molecules.

Nickel-catalyzed deaminative Sonogashira coupling of alkylpyridinium salts enabled by NN2 pincer ligand

Alkynes are amongst the most valuable functional groups in organic chemistry and widely used in chemical biology, pharmacy, and materials science. However, the preparation of alkyl-substituted alkynes still remains elusive. Here, we show a nickel-catalyzed deaminative Sonogashira coupling of alkylpyridinium salts. Key to the success of this coupling is the development of an easily accessible and bench-stable amide-type pincer ligand. This ligand allows naturally abundant alkyl amines as alkylating agents in Sonogashira reactions, and produces diverse alkynes in excellent yields under mild conditions. Salient merits of this chemistry include broad substrate scope and functional group tolerance, gram-scale synthesis, one-pot transformation, versatile late-stage derivatizations as well as the use of inexpensive pre-catalyst and readily available substrates. The high efficiency and strong practicability bode well for the widespread applications of this strategy in constructing functional molecules, materials, and fine chemicals.

Alkynes are amongst the most valuable functional groups in organic chemistry, however, the preparation of alkyl-substituted alkynes still remains elusive. Here the authors show a nickel-catalyzed deaminative Sonogashira coupling of alkylpyridinium salts.

Nickel-Catalyzed One-Pot Carbonylative Synthesis of 2-Mono- and 2,3-Disubstituted Thiochromenones from 2-Bromobenzenesulfonyl Chlorides and Alkynes

A nickel-catalyzed one-pot carbonylation reaction of 2-bromobenzenesulfonyl chlorides with alkynes for the synthesis of thiochromenones has been established. Both terminal and internal alkynes were suitable substrates in this carbonylative transformation, and a broad range of 2-mono- and 2,3-disubstituted thiochromenone products were obtained in moderate to good yields with quite high functional group compatibility. Notably, this procedure presents the first example of nickel-catalyzed carbonylative synthesis of thiochromenones with 2-bromobenzenesulfonyl chlorides as a promising sulfur precursor.

Copper-Catalyzed Carbonylative Coupling of Alkyl Halides

Transition metal-catalyzed carbonylation reactions represent a direct and atom-economical approach to introduce oxygen functionality into organic compounds, with CO acting as an inexpensive and readily available C1 feedstock. Despite the long history of carbonylation catalysis, including many processes that have been industrialized at bulk scale, there remain several challenges to tackle. For example, noble metals such as Pd, Rh, and Ir are typically used as catalysts for carbonylation reactions, rather than earth-abundant alternatives. Additionally, while carbonylation of C(sp²)-hybridized substrates (e.g., aryl halides) is well-known, carbonylation of unactivated alkyl electrophiles, especially where β-hydride elimination can compete with desired CO migratory insertion at the catalyst site, remains challenging for many systems. Recently, base metal catalysis based on Mn, Co, and other metals has enabled advances in carbonylative coupling of alkyl electrophiles, though the nucleophiles are often limited to alcohols or amines to generate esters or amides as products. Thus, we have targeted base metal-catalyzed carbonylative C-C and C-E (E = N, H, Si, B) coupling reactions as a method for approaching diverse carbonyl compounds of synthetic importance.Initially, we designed a heterobimetallic catalyst platform for carbonylative C-C coupling of alkyl halides with arylboronic esters (i.e., carbonylative Suzuki-Miyaura coupling) to generate aryl alkyl ketones. Subsequently, we developed multicomponent carbonylation reactions of alkyl halides using NHC-Cu catalysts (NHC = N-heterocyclic carbene). These reactions operate by radical mechanisms, converting alkyl halides into either acyl radical or acyl halide intermediates that undergo subsequent C-C or C-E coupling at the Cu site. This mechanistic paradigm is relatively novel in the metal-catalyzed carbonylation area, allowing us to discover a previously unexplored chemical space in carbonylative coupling catalysis. We have successfully developed the following reactions: (a) hydrocarbonylative coupling of alkynes with alkyl halides; (b) borocarbonylative coupling of alkynes with alkyl halides; (c) reductive aminocarbonylation of alkyl halides with nitroarenes; (d) reductive carbonylation of alkyl halides; (e) carbonylative silylation of alkyl halides; (f) carbonylative borylation of alkyl halides. These reactions provide a broad range of valuable products including ketones, allylic alcohols, β-borylenones, amides, alcohols, acylsilanes, and acylborons in an efficient manner. Notably, the preparation of some of these products has previously required multistep syntheses, harsh conditions, or specialized reagents. By contrast, the multicomponent coupling platform that we have developed requires only readily available building blocks and rapidly increases molecular complexity in a single synthetic manipulation.

A Nickel(II)-Mediated Thiocarbonylation Strategy for Carbon Isotope Labeling of Aliphatic Carboxamides

A series of pharmaceutically relevant small molecules and biopharmaceuticals bearing aliphatic carboxamides have been successfully labeled with carbon-13. Key to the success of this novel carbon isotope labeling technique is the observation that ¹³ C-labeled Ni^II -acyl complexes, formed from a ¹³ CO insertion step with Ni^II -alkyl intermediates, rapidly react in less than one minute with 2,2'-dipyridyl disulfide to quantitatively form the corresponding 2-pyridyl thioesters. Either the use of ¹³ C-SilaCOgen or ¹³ C-COgen allows for the stoichiometric addition of isotopically labeled carbon monoxide. Subsequent one-pot acylation of a series of structurally diverse amines provides the desired ¹³ C-labeled carboxamides in good yields. A single electron transfer pathway is proposed between the Ni^II -acyl complexes and the disulfide providing a reactive Ni^III -acyl sulfide intermediate, which rapidly undergoes reductive elimination to the desired thioester. By further optimization of the reaction parameters, reaction times down to only 11 min were identified, opening up the possibility of exploring this chemistry for carbon-11 isotope labeling. Finally, this isotope labeling strategy could be adapted to the synthesis of ¹³ C-labeled liraglutide and insulin degludec, representing two antidiabetic drugs.

Nickel-catalyzed cascade carbonylative synthesis of N-benzoyl indoles from 2-nitroalkynes and aryl iodides

A nickel-catalyzed carbonylative cyclization of 2-nitroalkynes and aryl iodides has been developed for the expedite construction of N-benzoyl indole scaffolds.

Nickel-Catalyzed Four-Component Carbocarbonylation of Alkenes under 1 atm of CO

Transition-metal-catalyzed carbonylation is one of the most straightforward strategies to prepare carbonyl compounds. However, compared to well-established noble-metal-catalyzed carbonylation reactions, analogue coupling via base-metal, nickel catalysis has received less attention because of the easy formation of highly toxic and unreactive Ni(CO)₄ species between Ni(0) and CO. To date, the use of inexpensive and widely available carbon monoxide (CO) gas for nickel-catalyzed carbonylation reaction remains challenging, and nickel-catalyzed four-component carbonylative reaction has not been reported yet. Here, we report a highly selective nickel-catalyzed four-component carbocarbonylation of alkenes under 1 atm (1 atm) of CO gas to efficiently achieve an array of complex carbonyl compounds, including fluorinated amino acids and oligopeptides of great interest in medicinal chemistry and chemical biology. This reaction relies on a nickel-catalyzed one-pot cascade process to assemble CO, arylboronic acids, and difluoroalkyl electrophiles across the carbon-carbon double bond of alkenes, paving a new way for base-metal-catalyzed carbonylative cascade reaction.

Palladium-Catalyzed Secondary Benzylic Imidoylative Reactions

Reported herein is a palladium-catalyzed secondary benzylic imidoylative Negishi reaction leveraging the sterically bulky aromatic isocyanides as the imine source. This method allows the facile access of alkyl-, (hetero)aryl-, and alkynylzinc reagents to afford various α-substituted phenylacetone products under mild acidic hydrolysis, which are ubiquitous motifs in many pharmaceuticals and biologically active compounds. The diastereoselective reduction of imine can be accomplished to provide the expedient conversion of secondary benzylic halide into α-substituted phenethylamine derivatives with high atom economy.

Controlled Release of Reactive Gases: A Tale of Taming Carbon Monoxide

This Personal Account describes the development of air-stable and solid precursors for on-demand release of carbon monoxide. In combination with the development of a two-chamber reactor, COware®, CO liberation can be achieved under safe working conditions, as well as allowing transition metal-mediated carbonylations with stoichiometric carbon monoxide. Particularly appealing is the adaptability of this chemical technology for the preparation of carbon isotope labeled bioactive compounds.

Nickel-Catalyzed Formal Aminocarbonylation of Secondary Benzyl Chlorides with Isocyanides

Phenylacetamides represent versatile feedstocks in synthetic chemistry, widely existing in drug molecules and natural products. Herein, we disclose a nickel-catalyzed formal aminocarbonylation of secondary benzyl chlorides with isocyanides yielding α-substituted phenylacetamide with steric hindrance, which is synthetically challenging via palladium-catalyzed aminocarbonylation. The reaction features wide functional group tolerance under mild conditions, highlighted by the tolerance of various aromatic halide (-Cl, -Br, -I) and heteroaromatic rings (pyridine and pyrazine).

Nickel-Catalyzed Formal Aminocarbonylation of Unactivated Alkyl Iodides with Isocyanides

Herein, we disclose a Ni-catalyzed formal aminocarbonylation of primary and secondary unactivated aliphatic iodides with isocyanides to afford alkyl amide, which proceeds via the selective monomigratory insertion of isocyanides with alkyl iodides, subsequent β-hydride elimination, and hydrolysis process. The reaction features wide functional group tolerance under mild conditions. Additionally, the selective, one-pot hydrolysis of reaction mixture under acid conditions allows for expedient synthesis of the corresponding alkyl carboxylic acid.

Direct Access to Isotopically Labeled Aliphatic Ketones Mediated by Nickel(I) Activation

An extensive range of functionalized aliphatic ketones with good functional-group tolerance has been prepared by a Ni^I -promoted coupling of either primary or secondary alkyl iodides with NN₂ pincer Ni^II -acyl complexes. The latter were easily accessed from the corresponding Ni^II -alkyl complexes with stoichiometric CO. This Ni-mediated carbonylative coupling is adaptable to late-stage carbon isotope labeling, as illustrated by the preparation of isotopically labelled pharmaceuticals. Preliminary investigations suggest the intermediacy of carbon-centered radicals.