Nickel-catalyzed Suzuki-Miyaura cross-couplings of aldehydes

Dehomologative C-C Borylation of Aldehydes and Alcohols via a Rh-Catalyzed Dehydroformylation-Borylation Relay

The dehomologative conversion of linear or α-methyl aldehydes to vinyl boronates is achieved via a one-pot sequence of rhodium-catalyzed transfer dehydroformylation and transfer borylation of the resulting alkenes. Similarly, allylic or aliphatic alcohols are converted to vinyl boronates through a sequence involving, respectively, rhodium-catalyzed isomerization or transfer dehydrogenation to aldehyde intermediates, followed by dehydroformylation-borylation. The vinyl boronates can be further hydrogenated to alkyl boronates using the same rhodium precatalyst, enabling all five catalytic steps with a single catalyst system.

The impact of earth-abundant metals as a replacement for Pd in cross coupling reactions

Substitution of one metal catalyst for another is not as straightforward as simply justifying this change based on the availability and/or cost of the metals. Methodologies to properly assess options for reaction design, including multiple factors like a metal's availability, cost, or environmental indicators have not advanced at the pace needed, leaving decisions to be made along these lines more challenging. Isolated indicators can lead to conclusions being made in too hasty a fashion. Therefore, an extensive life cycle-like assessment was performed documenting that the commonly held view that methods using earth-abundant metals (and in this case study, Ni) are inherently green replacements for methods using palladium in cross-coupling reactions, and Suzuki-Miyaura couplings, in particular, is an incomplete analysis of the entire picture. This notion can be misleading, and unfortunately derives mainly from the standpoint of price, and to some degree, relative natural abundance associated with the impact of mining of each metal. A more accurate picture emerges when several additional reaction parameters involved in the compared couplings are considered. The analysis points to the major impact that use of organic solvents has in these couplings, while the metals themselves actually play subordinate roles in terms of CO2-release into the environment and hence, the overall carbon footprint (i.e., climate change). The conclusion is that a far more detailed analysis is required than that typically being utilized.

Design and discovery of anthranilamide derivatives as a potential treatment for neurodegenerative disorders via targeting cholinesterases and monoamine oxidases

Neurodegenerative diseases with progressive cellular loss of the central nervous system and elusive disease etiology provide a continuous impetus to explore drug discovery programmes aiming at identifying robust and effective inhibitors of cholinesterase and monoamine oxidase enzymes. We herein present a concise library of anthranilamide derivatives involving a palladium-catalyzed Suzuki-Miyaura cross-coupling reaction to install the diverse structural diversity required for the desired biological action. Using Ellman's method, cholinesterase inhibitory activity was performed against AChE and BuChE enzymes. In vitro assay results demonstrated that anthranilamides are potent inhibitors with remarkable potency. Compound 6k emerged as the lead candidate and dual inhibitor of both enzymes with IC50 values of 0.12 ± 0.01 and 0.49 ± 0.02 μM against AChE and BuChE, respectively. Several other compounds were found as highly potent and selective inhibitors. Anthranilamide derivatives were also tested against monoamine oxidase (A and B) enzymes using fluorometric method. In vitro data revealed compound 6h as the most potent inhibitor against MAO-A, showing an IC50 value of 0.44 ± 0.02 μM, whereas, compound 6k emerged as the top inhibitor of MAO-B with an IC50 value of 0.06 ± 0.01 μM. All the lead inhibitors were analyzed for the identification of their mechanism of action using Michaelis-Menten kinetics experiments. Compound 6k and 6h depicted a competitive mode of action against AChE and MAO-A, whereas, a non-competitive and mixed-type of inhibition was observed against BuChE and MAO-B by compounds 6k. Molecular docking analysis revealed remarkable binding affinities of the potent inhibitors with specific residues inside the active site of receptors. Furthermore, molecular dynamics simulations were performed to explore the ability of potent compounds to form energetically stable complexes with the target protein. Finally, in silico ADME calculations also demonstrated that the potent compounds exhibit promising pharmacokinetic profile, satisfying the essential criteria for drug-likeness. Altogether, the findings reported in the current work clearly suggest that the identified anthranilamide derivatives have the potential to serve as effective drug candidates for future investigations.

Unveiling Pre-Transmetalation Intermediates in Base-Free Suzuki-Miyaura Cross-Couplings: A Computational Study

The pre-transmetalation intermediates are critically important in Suzuki-Miyaura cross-coupling (SMC) reactions and have become a hot spot of the current research. However, the pre-transmetalation intermediates under base-free conditions have not been clear. Herein, a comprehensive theoretical study is performed on the base-free Pd-catalyzed desulfonative SMC reaction. The fragile coordination feature and the acceleration role of the RuPhos chelate ligand are revealed. The hydrogen-bond complex between the Pd-F complex and aryl boronic acid is identified as an important pre-transmetalation intermediate, which increases the energy span to 32.5 kcal/mol. The controlling factor for the formation of the hydrogen-bond complexes is attributed to the electronegativities of halogen atoms in the metal halide complexes. What is more, other reported SMC reaction systems involving metal halide complexes and aryl boronic acids are reconsidered and suggest that the hydrogen-bond complexes widely exist as stable pre-transmetalation intermediates with influencing the catalytic activities. The earth-abundant Ni-catalyzed desulfonative SMC reaction is further designed and predicted to have a higher activity than the original Pd-catalyzed SMC reaction.

Pyrimidine-morpholine hybrids as potent druggable therapeutics for Alzheimer's disease: Synthesis, biochemical and in silico analyses

The identification of effective and druggable cholinesterase inhibitors to treat progressive neurodegenerative Alzheimer's disorder remains a continuous drug discovery hunt. In this perspective, the present study investigates the design and discovery of pyrimidine-morpholine hybrids (5a-l) as potent cholinesterase inhibitors. Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction was employed to introduce the structural diversity on the pyrimidine heterocyclic core. A range of commercially available boronic acids was successfully coupled showing a high functional group tolerance. In vitro cholinesterase inhibitory potential using Ellman's method revealed significantly strong potency. Compound 5h bearing a meta-tolyl substituent at 2-position of pyrimidine ring emerged as a lead candidate against AChE with an inhibitory potency of 0.43 ± 0.42 µM, ∼38-fold stronger value than neostigmine (IC50 = 16.3 ± 1.12 µM). Compound 5h also showed the lead inhibition against BuChE with an IC50 value of 2.5 ± 0.04 µM. The kinetics analysis of 5h revealed the non-competitive mode of inhibition against AChE whereas computational modelling results of potent leads depicted diverse contacts with the binding site amino acid residues. Molecular dynamics simulations revealed the stability of biomolecular system, while, ADME analysis demonstrated druglikeness behaviour of potent compounds. Overall, the investigated pyrimidine-morpholine scaffold presented a remarkable potential to be developed as efficacious anti-Alzheimer's drugs.

Carbon-Carbon Bond Cleavage for Late-Stage Functionalization

Late-stage functionalization (LSF) introduces functional group or structural modification at the final stage of the synthesis of natural products, drugs, and complex compounds. It is anticipated that late-stage functionalization would improve drug discovery's effectiveness and efficiency and hasten the creation of various chemical libraries. Consequently, late-stage functionalization of natural products is a productive technique to produce natural product derivatives, which significantly impacts chemical biology and drug development. Carbon-carbon bonds make up the fundamental framework of organic molecules. Compared with the carbon-carbon bond construction, the carbon-carbon bond activation can directly enable molecular editing (deletion, insertion, or modification of atoms or groups of atoms) and provide a more efficient and accurate synthetic strategy. However, the efficient and selective activation of unstrained carbon-carbon bonds is still one of the most challenging projects in organic synthesis. This review encompasses the strategies employed in recent years for carbon-carbon bond cleavage by explicitly focusing on their applicability in late-stage functionalization. This review expands the current discourse on carbon-carbon bond cleavage in late-stage functionalization reactions by providing a comprehensive overview of the selective cleavage of various types of carbon-carbon bonds. This includes C-C(sp), C-C(sp2), and C-C(sp3) single bonds; carbon-carbon double bonds; and carbon-carbon triple bonds, with a focus on catalysis by transition metals or organocatalysts. Additionally, specific topics, such as ring-opening processes involving carbon-carbon bond cleavage in three-, four-, five-, and six-membered rings, are discussed, and exemplar applications of these techniques are showcased in the context of complex bioactive molecules or drug discovery. This review aims to shed light on recent advancements in the field and propose potential avenues for future research in the realm of late-stage carbon-carbon bond functionalization.

DFT Mechanistic Insights into the Ni(II)-Catalyzed Enantioselective Arylative Cyclization of Tethered Allene-Ketones

Density functional theory (DFT) has provided a detailed mechanistic picture for the redox neutral nickel(II)-catalyzed arylative cyclization reactions of a tethered allene-ketone with arylboronic acids. A mechanistic rationale for the high diastereo- and enantioselectivity achieved experimentally at high reaction temperature was uncovered through modeling the reaction with a chiral ligand and the predicted stereochemical outcome corroborates with experimental results. An unprecedented mechanism for the base-free organoboron transmetalation was revealed and the regioselectivity of migratory insertion of tethered allene-ketones as well as the stability of the possible allylnickel isomers (σ-allyl vs π-allyl) were clarified. The multifaceted nature of the reaction is revealed with certain elementary steps preferring cationic compared to the neutral state.

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.

Divergent Acyl and Decarbonylative Liebeskind-Srogl Cross-Coupling of Thioesters by Cu-Cofactor and Pd-NHC (NHC = N-Heterocyclic Carbene) Catalysis

Transition-metal-catalyzed cross-coupling reactions of thioesters by selective acyl C(O)-S cleavage have emerged as a powerful platform for the preparation of complex molecules. Herein, we report divergent Liebeskind-Srogl cross-coupling of thioesters by Pd-NHC (NHC = N-heterocyclic carbene) catalysis. The reaction provides straightforward access to functionalized ketones by highly selective C(acyl)-S cleavage under mild conditions. Most crucially, the conditions enable direct functionalization of a range of complex pharmaceuticals decorated with a palette of sensitive functional groups, providing attractive products for medicinal chemistry programs. Furthermore, decarbonylative Liebeskind-Srogl cross-coupling by C(acyl)-S/C(aryl)-C(O) cleavage is reported. Cu metal cofactor directs the reaction pathway to acyl or decarbonylative pathway. This reactivity is applicable to complex pharmaceuticals. The reaction represents the mildest decarbonylative Suzuki cross-coupling discovered to date. The Cu-directed divergent acyl and decarbonylative cross-coupling of thioesters opens up chemical space in complex molecule synthesis.

Protoboration of Alkynes and Miyaura Borylation Catalyzed by Low Loadings of Palladium

The versions of Miyaura borylation and protoboration of alkynes catalyzed by low loadings of palladium (400 mol ppm = 0.04 mol %) have been developed. These transformations have a broad substrate scope, good functional-group compatibility, and gram-scale synthetic ability.

Rhodium-Catalyzed Deuterated Tsuji-Wilkinson Decarbonylation of Aldehydes with Deuterium Oxide

The recent surge in the applications of deuterated drug candidates has rendered an urgent need for diverse deuterium labeling techniques. Herein, an efficient Rh-catalyzed deuterated Tsuji-Wilkinson decarbonylation of naturally available aldehydes with D₂O is developed. In this reaction, D₂O not only acts as a deuterated reagent and solvent but also promotes Rh-catalyzed decarbonylation. In addition, decarbonylative strategies for the synthesis of terminal monodeuterated alkenes from α,β-unsaturated aldehydes are within reach.

Facile Synthesis of 2-Methylnicotinonitrile through Degenerate Ring Transformation of Pyridinium Salts

Nucleophilic recyclization of pyridinium salts involving a CCN interchange ring transformation for the synthesis of 2-methylnicotinonitrile derivatives was herein developed. 3-Aminocrotononitrile (3-ACN) produced in situ from CH₃CN acted as a C-nucleophile, as well as the source of CH₃ and CN groups, which was supported by isotope-labeling and control experiments.

Decarbonylative Pd-Catalyzed Suzuki Cross-Coupling for the Synthesis of Structurally Diverse Heterobiaryls

Heteroaromatic biaryls are core scaffolds found in a plethora of pharmaceuticals; however, their direct synthesis by the Suzuki cross-coupling is limited to heteroaromatic halide starting materials. Here, we report a direct synthesis of diverse nitrogen-containing heteroaromatic biaryls by Pd-catalyzed decarbonylative Suzuki cross-coupling of widely available heterocyclic carboxylic acids with arylboronic acids. The practical and modular nature of this cross-coupling enabled the straightforward preparation of >45 heterobiaryl products using pyridines, pyrimidines, pyrazines, and quinolines in excellent yields. We anticipate that the modular nature of this protocol will find broad application in medicinal chemistry and drug discovery research.

Selective Activation of Unstrained C(O)-C Bond in Ketone Suzuki-Miyaura Coupling Reaction Enabled by Hydride-Transfer Strategy

A Rh(I)-catalyzed ketone Suzuki-Miyaura coupling reaction of benzylacetone with arylboronic acid is developed. Selective C(O)-C bond activation, which employs aminopyridine as a temporary directing group and ethyl vinyl ketone as a hydride acceptor, occurs on the alkyl chain containing a β-position hydrogen. A series of acetophenone products were obtained in yields up to 75%.

DFT study on the ruthenium-catalyzed decarbonylative annulation of an alkyne with a six-membered hydroxychromone via C–H/C–C activation

Both steady-state approximation and the modified energy span model have been employed to determine the TOF-determining transition state and TOF-determining intermediate for the title catalytic reaction.

Visible-light-induced transition metal and photosensitizer free decarbonylative addition of amino-arylaldehydes to ketones

The decarbonylative-coupling reaction is generally promoted by transition metals (via organometallic complexes) or peroxides (via radical intermediates), often at high temperatures to facilitate the CO release. Herein, a visible-light-induced, transition metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes at room temperature is reported. Tertiary/secondary alcohols were obtained in moderate to excellent yields promoted by using CsF under mild conditions. The detailed mechanistic investigation showed that the reaction proceeded through photoexcitation–decarbonylation of the aldehyde to generate an aromatic anion, followed by its addition to ketones/aldehydes. The reaction mechanism was verified by the density functional theory (DFT) calculations.

A visible-light-induced, transition-metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes via anion intermediates at room temperature is developed.

Transition metal-catalyzed arylation of unstrained C-C single bonds

Carbon-carbon bond activation is one of the most challenging and important research areas in organic chemistry. Selective C-C bond activation of unstrained substrates is difficult to achieve owing to its inert nature and competitive side reactions, but the ubiquitous presence of C-C bonds in organic molecules makes this transformation attractive and of vital importance. Moreover, transition metal-catalyzed arylation of unstrained C-C single bonds can realize the cleavage of old C-C bonds and introduce important aryl groups into the carbon chain to construct new C-C bonds at the same time, providing a powerful and straightforward method to reconstruct the skeleton of the molecules. In recent years, considerable progress has been made in the area of direct arylation of C-C bonds, and β-C elimination or oxidative addition strategies play key roles in these transformations. This review summarizes recent achievements of transition metal-catalyzed arylation of unstrained C-C bonds, demonstrated by various kinds of substrates including alcohol, nitrile and carbonyl compounds, and each example is detailed by its corresponding mechanism, catalytic system and scope of the substrate.

Mechanistic Aspects of the Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction

The story of C-C bond formation includes several reactions, and surely Suzuki-Miyaura is among the most outstanding ones. Herein, a brief historical overview of insights regarding the reaction mechanism is provided. In particular, the formation of the catalytically active species is probably the main concern, thus the preactivation is in competition with, or even assumes the role of the rate determining step (rds) of the overall reaction. Computational chemistry is key in identifying the rds and thus leading to milder conditions on an experimental level by means of predictive catalysis.

Metal-catalysed C-Het (F, O, S, N) and C-C bond arylation

The formation of C-aryl bonds has been the focus of intensive research over the last decades for the construction of complex molecules from simple, readily available feedstocks. Traditionally, these strategies involve the coupling of organohalides (I, Br, Cl) with organometallic reagents (Mg, Zn, B, Si, Sn,…) such as Kumada-Corriu, Negishi, Suzuki-Miyaura, Hiyama and Sonogashira cross-couplings. More recently, alternative methods have provided access to these products by reactions with less reactive C-Het (F, O, S, N) and C-C bonds. Compared to traditional methods, the direct cleavage and arylation of these chemical bonds, the essential link in accessible feedstocks, has become increasingly important from the viewpoint of step-economy and functional-group compatibility. This comprehensive review aims to outline the development and advances of this topic, which was organized into (1) C-F bond arylation, (2) C-O bond arylation, (3) C-S bond arylation, (4) C-N bond arylation, and (5) C-C bond arylation. Substantial attention has been paid to the strategies and mechanistic investigations. We hope that this review can trigger chemists to discover more efficient methodologies to access arylation products by cleavage of these C-Het and C-C bonds.

Decarbonylative Sonogashira Cross-Coupling of Carboxylic Acids

Decarbonylative Sonogashira cross-coupling of carboxylic acids by palladium catalysis is presented. The carboxylic acid is activated in situ by the formation of a mixed anhydride and further decarbonylates using the Pd(OAc)₂/Xantphos system to provide an aryl-Pd intermediate, which is intercepted by alkynes to access the traditional Pd(0)/(II) cycle using carboxylic acids as ubiquitous and orthogonal electrophilic cross-coupling partners. The methodology efficiently constructs new C(sp²)-C(sp) bonds and can be applied to the derivatization of pharmaceuticals. Mechanistic studies give support to decarbonylation preceding transmetalation in this process.

Suzuki–Miyaura cross coupling reaction: recent advancements in catalysis and organic synthesis

Suzuki–Miyaura cross coupling reaction (SMCR) – A milestone in the synthesis of C–C coupled compounds.

Ni/Pd-catalyzed Suzuki-Miyaura cross-coupling of alcohols and aldehydes and C-N cross-coupling of nitro and amines via domino redox reactions: base-free, hydride acceptor-free

Domino oxidation-Suzuki-Miyaura cross-coupling of benzyl alcohols with phenylboronic acid and domino reduction-C-N cross-coupling of the nitro compounds with aryl halides were carried out using a strong Ni/Pd bimetallic redox catalyst. The catalyst bearing a copolymer with two Ni/Pd coordinated metals in porphyrin (derived from demetalated chlorophyll b) and salen-type ligands, and pyridine moiety as a base functionality all immobilized on magnetite NPs was synthesised and characterized. The domino oxidation cross-coupling reaction was accomplished under molecular O2 in the absence of any hydride acceptor or/and base. Also, the domino reduction C-N cross-coupling reaction was performed in the presence of NaBH4 without the need for any base and co-reductant. This multifunctional catalyst gave moderate to good yields for both coupling reactions with high chemoselectivity. A wide investigation was conducted to determine its mechanism and chemoselectivity.

Synthesis of Biaryls via Decarbonylative Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling of Aryl Anhydrides

Transition metal-catalyzed cross-couplings have been widely employed in the synthesis of many important molecules in synthetic chemistry for the construction of diverse C-C bonds. Conventional cross-coupling reactions require active electrophilic coupling partners, such as organohalides or sulfonates, which are not environmentally friendly enough. Herein, we disclose the first nickel-catalyzed Suzuki-Miyaura cross-coupling of aryl anhydrides and arylboronic acids for the synthesis of biaryls in a decarbonylation manner. The reaction tolerates a wide range of electron-withdrawing, electron-neutral, and electron-donating substituents in this process.

Ligand Steric Effects of α-Diimine Nickel(II) and Palladium(II) Complexes in the Suzuki-Miyaura Cross-Coupling Reaction

Nickel catalysts represent a low cost and environmentally friendly alternative to palladium-based catalytic systems for Suzuki-Miyaura cross-coupling (SMC) reactions. However, nickel catalysts have suffered from poor air, moisture, and thermal stabilities, especially at high catalyst loading, requiring controlled reaction conditions. In this report, we examine a family of mono- and dinuclear Ni(II) and Pd(II) complexes with a diverse and versatile α-diimine ligand environment for SMC reactions. To evaluate the ligand steric effects, including the bite angle in the reaction outcomes, the structural variation of the complexes was achieved by incorporating iminopyridine- and acenaphthene-based ligands. Moreover, the impact of substrate bulkiness was investigated by reacting various aryl bromides with phenylboronic acid, 2-naphthylboronic acid, and 9-phenanthracenylboronic acid. Yields were the best with the dinuclear complex, being nearly quantitative (93-99%), followed by the mononuclear complexes, giving yields of 78-98%. Consequently, α-diimine-based ligands have the potential to deliver Ni-based systems as sustainable catalysts in SMC.

Decarbonylative Suzuki-Miyaura Cross-Coupling of Aroyl Chlorides

Herein, we report a catalyst system for Pd-catalyzed decarbonylative Suzuki-Miyaura cross-coupling of aroyl chlorides with boronic acids to furnish biaryls. This strategy is suitable for a broad range of common aroyl chlorides and boronic acids. The synthetic utility is highlighted in the direct late-stage functionalization of pharmaceuticals and natural products capitalizing on the presence of carboxylic acid moiety. Extensive mechanistic and DFT studies provide key insight into the reaction mechanism and high decarbonylative cross-coupling selectivity.

Nickel-Catalyzed Asymmetric Addition of Aromatic Halides to Ketones: Highly Enantioselective Synthesis of Chiral 2,3-Dihydrobenzofurans Containing a Tertiary Alcohol

A highly enantioselective and straightforward synthetic procedure to chiral 3-hydroxy-2,3-dihydrobenzofurans has been developed by nickel/bisoxazoline-catalyzed intramolecular asymmetric addition of aryl halides to unactivated ketones, giving 2,3-dihydrobenzofurans with a chiral tertiary alcohol at the C-3 position in good yields and excellent enantioselectivities (up to 92% yield and 98% ee). The gram-scale reaction also proceeded smoothly without a loss of yield and enantioselectivity.

Reductive coupling of imines with redox-active esters by visible light photoredox organocatalysis

The direct alkylation of imines with redox-active esters by visible light photoorganocatalysis provides a direct way for accessing α-branched secondary amines which are found in numerous bioactive molecules.

Aldehydes as Alkylating Agents for Ketones

Common and non-toxic aldehydes are proposed as reagents for alkylation of ketones instead of carcinogenic alkyl halides. The developed reductive alkylation reaction proceeds in the presence of the commercially available ruthenium catalyst [(cymene)RuCl₂ ]₂ (as low as 250 ppm) and carbon monoxide as the reducing agent. The reaction works well for a broad substrate scope, including aromatic and aliphatic aldehydes and ketones. It can be carried out without a solvent and often gives nearly quantitative yields of the products. This straightforward and cost-effective method is promising not only for laboratory application but also for industry, which produces carbon monoxide as a large-scale waste product.

Nickel-Catalyzed Selective Reduction of Carboxylic Acids to Aldehydes

The direct reduction of carboxylic acids to aldehydes is a fundamental transformation in organic synthesis. The combination of an air-stable Ni precatalyst, dimethyl dicarbonate as an activator, and silane reductant effects this reduction for a wide variety of substrates, including pharmaceutically relevant structures, in good yields and with no overreduction to alcohols. Moreover, this methodology is scalable, allows access to deuterated aldehydes, and is also compatible with one-pot utilization of the aldehyde products.