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

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.

Photocatalytic Synthesis of Difluorinated Glycoamino Acids and Neoglycopeptides via Hydrodifluoroacetamidation of Vinyl-C-glycosides

A photocatalytic approach for the synthesis of difluorinated glycoamino acids and neoglycopeptides from bromodifluoroacetamides and sugar-derived olefins is presented. This method stands out because of its simplicity, atomic economy, and mild reaction conditions, allowing compatibility with both natural and unnatural amino acids and peptides. Additionally, it demonstrates efficacy across a variety of carbohydrates, including furanoses, pyranoses, pentose, hexoses, and disaccharides, accommodating an extensive range of protecting groups, even in their deprotected forms.

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.

Synthesis of 4-(Bromodifluoromethylseleno) Isocoumarins via Selenolation/Lactonization of 2-Alkynylbenzoates Enabled by a Multi-Component Reagents System

p-CF3BnSeCF2Br was developed as a bromodifluoromethylselenonating reagent, which was utilized by combining with mCPBA and Tf2O for the synthesis of 4-(bromodifluoromethylseleno) isocoumarins via the selenolation/lactonization of 2-alkynylbenzoates. The transformation was postulated to proceed via a multicomponent reagents system-enabled sequence involving the oxidation of p-CF3BnSeCF2Br by mCPBA into its selenium sulfoxide, activation of the generated sulfoxide by Tf2O into the electrophilic p-CF3BnSeOCF2Br salt, and selenolation/lactonization of 2-alkynylbenzoates by the reactive electrophilic species into 4-(bromodifluoromethylseleno) isocoumarins.

Nickel-Catalyzed Cyclization/Carbonylation Reaction of N-Allylbromoacetamides with Arylboronic Acids toward 2-Pyrrolidinones

A straightforward and efficient nickel-catalyzed cyclization/carbonylation transformation of N-allylbromoacetamides toward the synthesis of 2-pyrrolidinone derivatives has been developed with arylboronic acids as the reaction partner. This transformation proceeds through a sequential single-electron-transfer pathway via 5-exo-trig cyclization and carbonyl insertion steps, furnishing a variety of 2-pyrrolidinone derivatives in good yields. Various useful functional groups were well tolerated. Moreover, formic acid is applied as the CO source here with nickel as the catalyst, which provides a good supplement for carbonylation chemistry and heterocycle synthesis.

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.

Palladium-Catalyzed Four-Component Radical Cascade Carbonylation Access to 2,3-Disubstituted Benzofuran Derivatives

Multicomponent radical tandem reactions have emerged as a crucial technique for synthesizing complex molecules in organic chemistry. In this study, we report a palladium-catalyzed four-component difluoroalkylative carbonylation of enynes and ethyl difluoroiodoacetate. This transformation proceeds through a multistep sequential reaction that introduces reactive difluoro and carbonyl groups while constructing the benzofuran skeleton. Moreover, a variety of valuable 2,3-disubstituted benzofuran derivatives were obtained in respectable yields with excellent functional group compatibility.

Nickel-Catalyzed Narasaka-Heck Cyclization Carbonylation of Unsaturated Oxime Esters with Arylboronic Acids

The Narasaka-Heck reaction is one of the most straightforward methods for constructing pyrroline derivatives. Herein, we report a novel nickel-catalyzed three-component carbonylation reaction, which cleverly realizes the continuous construction of C(sp3)-N bonds and C(sp3)-C(sp2) bonds and effectively promotes the synthesis of acyl-substituted pyrroline derivatives. Furthermore, this strategy not only expands the conversion pathway of γ,δ-unsaturated oxime esters but also provides a new method for the synthesis of nitrogen-containing heterocyclic compounds.

Ball-Milling-Enabled Nickel-Catalyzed Reductive 1,4-Alkylarylation of 1,3-Enynes under an Air Atmosphere

A ball-mill-enabled nickel-catalyzed 1,4-alkylarylation of 1,3-enynes with organic bromides has been developed, offering a versatile method for assembling tetrasubstituted allenes. This approach, the first of ball-milling-based remote radical coupling, overcomes the limitations of traditional solution-phase methods, such as the need for air- and moisture-sensitive reagents, the use of bulk solvents, and prolonged reaction times. Given the outstanding performance of ball-milling-based radical reduction coupling reactions, we anticipate further advancements in sustainable and efficient synthetic methodologies.

Ni-catalyzed enantioselective three-component reductive alkylacylation of alkenes: modular access to structurally complex α-amino ketones

Chiral alpha-amino ketones have found extensive applications as functional molecules. A nickel-catalyzed, enantioselective, and fully intermolecular three-component 1,2-alkylacylation of N-acyl enamides has been realized with tertiary alkyl bromides and carboxylic acid-derived electrophiles as the coupling reagents. This reductive coupling strategy is operationally simple, exhibiting broad substrate scope and excellent functional group tolerance using readily available starting materials and allowing rapid access to structurally complex α-amino ketone derivatives in high enantioselectivity. A suitable chiral biimidazoline ligand together with additional chelation of the amide carbonyl group in a Ni alkyl intermediate facilitates the enantioselective control by suppressing the background reaction, accounting for the excellent enantioselectivity. Mechanistic studies indicated intermediacy of radical species.

Nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes to access allenes and dienes

The radical-mediated difunctionalization of 1,3-enynes facilitates rapid access to structurally diverse allenes and dienes. Whereas, owing to the existence of multiple active sites in conjugated 1,3-enynes, regulating selectivity in difunctionalized addition via a single transition-metal-catalyzed radical tandem process remains elusive. Herein, we disclose an intriguing protocol of substrate-controlled nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes with the assistance of sulfonyl chlorides and arylboronic acids. This valuable synthetic utility respectively delivers a series of highly functionalized and synthetically challenging allenyl sulfones and dienyl sulfones from fine-tuned 1,3-enynes by one step, which provides a facile approach for complex sulfone-containing drug molecules synthesis.

Nickel-Catalyzed Four-Component Carbonylation of 1,3-Butadiene To Access β,γ-Unsaturated Ketones

A new strategy to obtain β,γ-unsaturated ketones via the cross-coupling of 1,3-butadiene, alkyl bromides, and arylboronic acids under 1 bar of CO with nickel as the catalyst has been developed. This newly developed four-component carbonylation procedure features advantages including using a cheap catalytic system, high step economy, mild reaction conditions, and excellent 1,4-regioselectivity, thereby providing a sustainable and alternative tool for β,γ-unsaturated ketones production compared to the present tactics. To elucidate the application potential of this method, olefin synthons are derived from the representative coupling product.

Regioselective synthesis of N-containing polycyclic compounds via radical annulation cyclization of 1,7-dienes with aldehydes

A convenient method for oxidant-promoted radical cascade acylation or decarbonylative alkylation of 1,7-dienes with aldehydes has been established. This method allows for the rapid construction of N-containing polycyclic skeletons in a highly regio- and stereoselective manner. This transformation provides a simple and efficient method for the preparation of a range of tetrahydro-6H-indeno[2,1-c]quinolinone derivatives by sequential formation of three new carbon-carbon bonds. Additionally, this radical cascade cyclization can selectively convert aldehydes into aroyl/primary aliphatic acyl radicals and secondary or tertiary alkyl radicals.

Iron-Catalyzed Aminoalkylative Carbonylative Cyclization of Alkenes toward α-Tetralones

Carbonylative multifunctionalization of alkenes is an efficient approach to introduce multiple functional groups into one molecule from easily available materials. Herein, we developed an iron-catalyzed radical relay carbonylative cyclization of alkenes with acetamides. Various α-tetralones can be constructed in moderate yields from readily available substrates with an earth-abundant iron salt as the catalyst.

Nickel-Catalyzed Hydrofluorination in Unactivated Alkenes: Regio- and Enantioselective C-F Bond Formation

Catalytic formation of a regio- and enantioselective C-F bond chiral center from readily available alkenes is a crucial goal, yet it continues to pose significant challenges in organic synthesis. Here, we report the regioselective formation of C-F bonds facilitated by NiH catalysis and a coordination directing strategy that enables precise hydrofluorination of both terminal and internal alkenes. Notably, we have optimized this methodology to achieve high enantioselectivity in creating aliphatic C-F stereogenic centers especially with β,γ-alkenyl substrates, using a tailored chiral Bn-BOx ligand. Another pivotal finding in our research is the identification of the (+)-nonlinear effect under optimized conditions, allowing for high enantioselectivity even with moderately enantiomerically enriched chiral ligands. Given the significant role of fluorine in pharmaceuticals and synthetic materials, this research offers essential insights into the regioselective and enantioselective formation of C-F bond chiral centers, paving the way for the efficient production of valuable fluorinated compounds.

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.

Palladium-Catalyzed Carbonylative Multicomponent Fluoroalkylation of 1,3-Enynes: Concise Construction of Diverse Cyclic Compounds

Multicomponent reactions, particularly those entailing four or more reagents, have presented a longstanding challenge due to the inherent complexities associated with balancing reactivity, selectivity, and compatibility. In this study, we describe a palladium-catalyzed multi-component fluoroalkylative carbonylation of 1,3-enynes. A series of products featuring three active functional groups-allene, fluoroalkyl, and carboxyl, were efficiently and selectively integrated in a single chemical operation. Furthermore, more intricate fluoroalkyl-substituted pyrimidinones can be constructed by simply altering the 1,3-bisnucleophilic reagent. This approach also provides a valuable strategy for the late-stage modification of naturally occurring molecules and concise construction of diverse cyclic compounds.

Enantioselective Palladium-Catalyzed Domino Carbonylative Heck Esterification of o-Iodoalkenylbenzenes with Arylboronic Acids

The current investigation presents an innovative palladium-catalyzed asymmetric carbonylative Heck esterification method. This approach facilitates the efficient synthesis of various chiral γ-ketoacid esters by utilizing o-alkenyliodobenzenes and arylboronic acids as primary substrates. This reaction achieves the creation of three carbon-carbon bonds, two carbon-oxygen bonds, and the establishment of a quaternary carbon center within a single step. The α-chiral γ-ketoacid esters were obtained in yields ranging from good to high yields, displaying enantiomeric excesses (ee's) levels up to 92% under mild reaction conditions.

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.

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.

Directed Nickel-Catalyzed Selective Arylhydroxylation of Unactivated Alkenes under Air

An expeditious and novel nickel-catalyzed selective arylhydroxylation of unactivated alkenes with arylboronic acids was developed. This protocol is compatible with β,γ- and γ,δ-alkene amides, including traditionally challenging internal alkenes, to provide important β-arylethylalcohol scaffolds. The free hydroxyl group in the final product could be smoothly further transformed into other functional groups. Control experiments indicated that the oxygen atom of the hydroxyl group in the product is derived from the oxygen in the air.

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.

Recent advances in the synthesis of fluorinated amino acids and peptides

The site-selective modification of amino acids, peptides, and proteins has always been an intensive topic in organic synthesis, medicinal chemistry, and chemical biology due to the vital role of amino acids in life. Among the developed methods, the site-selective introduction of fluorine functionalities into amino acids and peptides has emerged as a useful approach to change their physicochemical and biological properties. With the increasing demand for life science, the direct fluorination/fluoroalkylation of proteins has also received increasing attention because of the unique properties of fluorine atom(s) that can change the protein structure, increase their lipophilicity, and enable fluorine functionality as a biological tracer or probe for chemical biology studies. In this feature article, we summarized the recent advances in the synthesis of fluorinated amino acids and peptides, wherein two strategies have been discussed. One is based on the fluorinated building blocks to prepare fluorinated amino acids and peptides with diversified structures, including the transformations of fluorinated imines and nickel-catalyzed dicarbofunctionalization of alkenes with bromodifluoroacetate and its derivatives; the other is direct fluorination/fluoroakylation of amino acids, peptides, and proteins, in which the selective transformations of the functional groups on serine, threonine, tyrosine, tryptophan, and cysteine lead to a wide range of fluorinated α-amino acids, peptides, and proteins, featuring synthetic convenience and late-stage modification of biomacromolecules. These two strategies complement each other, wherein transition-metal catalysis and new fluoroalkylating reagents provide powerful tools to selectively access fluorinated amino acids, peptides, and proteins, showing the prospect of medicinal chemistry and chemical biology.

Palladium-Catalyzed Carbonylations: Application in Complex Natural Product Total Synthesis and Recent Developments

Carbon monoxide is a cheap and abundant C1 building block that can be readily incorporated into organic molecules to rapidly build structural complexity. In this Perspective, we outline several recent (since 2015) examples of palladium-catalyzed carbonylations in streamlining complex natural product total synthesis and highlight the strategic importance of these carbonylation reactions in the corresponding synthesis. The selected examples include spinosyn A, callyspongiolide, perseanol, schizozygane alkaloids, cephanolides, and bisdehydroneostemoninine and related stemona alkaloids. We also provide our perspective about the recent advancements and future developments of palladium-catalyzed carbonylations.

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.

Difluoroalkylative carbonylation of alkenes to access carbonyl difluoro-containing heterocycles: convenient synthesis of gemigliptin

Fluorinated heterocycles play a vital role in pharmaceutical and agrochemical industries. Hence, rapid and efficient construction of fluorinated heterocycles remains highly demanded. Herein, a difluoroalkylative carbonylative cyclization of unactivated alkenes and ethylene gas enabled by palladium catalysis has been developed for the first time toward the synthesis of α-carbonyl difluoro-modified glutarimides. This procedure can also be applied to the synthesis of GeMigliptin which is a medicine approved for the treatment of type 2 diabetes mellitus.

Ligand-free nickel catalyzed perfluoroalkylation of arenes and heteroarenes

We describe a "ligand-free" Ni-catalyzed perfluoroalkylation of heteroarenes to produce a diverse array of trfiluoromethyl, pentafluoroethyl and heptafluoropropyl adducts. Catalysis proceeds at room temperature via a radical pathway. The catalytic protocol is distinguished by its simplicity, and its wide scope demonstrates the potential in the late-stage functionalization of drug analogues and peptides.

Non-Noble Metal-Catalyzed Carbonylative Multi-Component Reactions

Carbonylative multi-component reactions (CMCR), having four or more kinds of starting materials, provide an efficient strategy for the preparation of polyfunctional carbonylated compounds. Diverse CMCR utilizing non-noble transition-metal catalysts have been developed. This review summarized and discussed the recent advances in non-noble metal-catalyzed carbonylative multi-component reactions.

Palladium-Catalyzed Perfluoroalkylative Carbonylation of 2-Allylaryl Trifluoromethanesulfonates: Base-Controlled Selective Access to β-Perfluoroalkyl Amides

A palladium-catalyzed perfluoroalkylative carbonylation of 2-allylaryl trifluoromethanesulfonates has been developed. A range of 2-allyl trifluoromethanesulfonates, perfluoroalkyl halides, and amines were applied in this tandem procedure to provide the corresponding β-perfluoroalkyl amides with good functional group tolerance and high chemoselectivity. The final products were controlled by the base applied.

Palladium-catalyzed difluoroalkylative carbonylation of styrenes toward difluoropentanedioates

The introduction of fluorine atoms into organic molecules is an attractive but challenging topic. In this work, an interesting palladium-catalyzed difluoroalkylative carbonylation of aryl olefins has been developed. A wide range of aryl olefins were transformed into the corresponding difluoropentanedioate compounds with good functional-group tolerance and excellent regioselectivity. Inexpensive ethyl bromodifluoroacetate acts both as a difluoroalkyl precursor and a nucleophile here. Additionally, a scale-up reaction was also performed successfully, and further transformations of the obtained product were shown as well.

CF3SO2Na-Mediated Five-Component Carbonylation of Triarylboroxines with TMSCF3 and THF/LiOH/NaI to Give Aroyloxyalkyl Iodides

Herein, we developed an efficient and transition-metal-free multicomponent coupling reaction for the synthesis of aroyloxyl alkyl iodides. In the reaction among 2,4,6-triarylboroxines, THF, TMSCF₃, LiOH, and NaI, five-component reactions could be precisely controlled by modulating CF₃SO₂Na, supplying one type of aroyloxyl alkyl iodides in moderate to high yields. The reaction exhibits good functional group tolerance and a wide substrate scope and can be easily transformed into other useful compounds. The mechanism is proposed on the basis of the control experiments.

Nickel-catalyzed Thioester Transfer Reaction with sp2-Hybridized Electrophiles

We report a thioacylation transfer reaction based on nickel-catalyzed C-C bond cleavage of thioesters with sp²-hybridized electrophiles. Aryl bromides, iodides, and alkenyl triflates can participate in thioester transfer reaction of aryl thioesters, affording a wide range of structurally diverse new thioesters in yields of up to 98% under mild reaction conditions. With this protocol, it is possible to construct alkenyl thioesters from the corresponding ketones through the generation of alkenyl triflates.

Nickel-Catalyzed Three-Component Alkylacylation of Alkenes Enabled by a Photoactive Electron Donor-Acceptor Complex

An electron donor-acceptor complex-enabled, nickel-catalyzed three-component net-reductive 1,2-alkylacylation of alkenes is developed. This conjunctive reductive acyl cross-coupling process obviates the use of an exogenous photocatalyst and a stoichiometric metal-based reductant, affording various synthetically useful 1,3-dicarbonyl compounds in good yields with a broad substrate scope and excellent functional group tolerance. Both alkyl and acyl electrophiles are derived from the highly abundant and readily accessible carboxylic acids, making the catalytic 1,2-dicarbofunctionalization more synthetically general and sustainable.

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.

Synthesis, structure, and electrochemical properties of [LNi(Rf)(C4F8)]- and [LNi(Rf)3]- complexes

The new anionic nickelate complexes [(MeCN)Ni(C₄F₈)(CF₃)]^-, [(MeCN)Ni(C₄F₈)(C₂F₅)]^-, [(IMes)Ni(C₄F₈)(CF₃)]^-, [(IMes)Ni(CF₃)₃]^- (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), and [(F-NHC)Ni(R_f)₃]^- (F-NHC = 1,3-bis(2,4-F₂Ph), 2,4,6-F₃Ph- or 3,4,5-F₃Ph)imidazol-2-ylidene; (R_f = CF₃ or C₂F₅) were synthesized and structurally characterized. The electrochemical properties of all new compounds were revealed by cyclic voltammetry studies and compared to the known CF₃ analogue [(MeCN)Ni(CF₃)₃]^-. The IMes-coordinated complexes exhibited initial oxidation events that were well-separated from a second oxidation process in the cyclic voltammograms. The complexes containing F-substituted NHC ligands [(F-NHC)Ni(CF₃)₃]^- are structurally quite similar to the IMes derivative and reveal also two separated oxidation waves in their cyclic voltammograms. The absolute potentials as well as the separation between the two waves vary with the substitution pattern, suggesting that the NHC ligand environment (NHC = N-heterocyclic carbene) is an interesting platform for the development of new redox-triggered reactions that release trifluoromethyl and perfluoroalkyl radicals upon oxidation.

Difluoroalkylation of Tertiary Amides and Lactams by an Iridium-Catalyzed Reductive Reformatsky Reaction

An iridium-catalyzed, reductive alkylation of abundant tertiary lactams and amides using 1-2 mol % of Vaska's complex (IrCl(CO)(PPh3)2), tetramethyldisiloxane (TMDS), and difluoro-Reformatsky reagents (BrZnCF2R) for the general synthesis of medicinally relevant α-difluoroalkylated tertiary amines is described. A broad scope (46 examples), including N-aryl- and N-heteroaryl-substituted lactams, demonstrated an excellent functional group tolerance. Furthermore, late-stage drug functionalizations, a gram-scale synthesis, and common downstream transformations proved the potential synthetic relevance of this new methodology.