Mild Pd-catalyzed aminocarbonylation of (hetero)aryl bromides with a palladacycle precatalyst

Redox-Neutral Decarboxylative Cross-Coupling of Oxamates with Aryl Bromides

Dual nickel-photoredox-enabled direct synthesis of amides through cross-coupling of cesium oxamates with aryl bromides has been developed. This methodology's key advantages are mild reaction conditions, utilizing organic dye as a photocatalyst, employing readily available starting chemicals as coupling partners, and late-stage carbamoylation of pharmaceutically relevant molecules. DFT studies suggested that the nickel catalytic cycle proceeds via a radical addition pathway prior to the oxidative insertion.

Recent advances in ligand-enabled palladium-catalyzed divergent synthesis

Developing efficient and straightforward strategies to rapidly construct structurally distinct and diverse organic molecules is one of the most fundamental tasks in organic synthesis, drug discovery and materials science. In recent years, divergent synthesis of organic functional molecules from the same starting materials has attracted significant attention and has been recognized as an efficient and powerful strategy. To achieve this objective, the proper adjustment of reaction conditions, such as catalysts, solvents, ligands, etc., is required. In this review, we summarized the recent efforts in chemo-, regio- and stereodivergent reactions involving acyclic and cyclic systems catalyzed by palladium complexes. Meanwhile, the reaction types, including carbonylative reactions, coupling reactions and cycloaddition reactions, as well as the probable mechanism have also been highlighted in detail.

Decarboxylative C-H silylation of N-heteroarenes with silanecarboxylic acids

Established decarboxylative Minisci reactions are limited to aliphatic carboxylic acids, as their analogs, silanecarboxylic acids, have been rarely investigated. Herein, we present a new decarboxylative Minisci-type reaction of N-heteroarenes with silanecarboxylic acids under photo- or silver-mediated conditions. This C-H silylation strategy provides efficient access to diverse N-heteroarylsilanes in moderate to excellent yields with high regioselectivity, among which Ag-catalysed decarboxylation of silanecarboxylic acids furnishes an unprecedented method for silyl radical generation.

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.

Palladium-Catalyzed Carbonylative Hiyama-Denmark Reaction toward the Synthesis of Aryl Carbonyl-Containing Oxindoles

A palladium-catalyzed domino Heck cyclization/carbonylative Hiyama-Denmark cross-coupling reaction between alkene-tethered aryl iodides and silylcarboxylic acids is presented. This reaction proceeds well without toxic carbon monoxide (CO) gas and has good functional group tolerance, providing an alternative access to carbonyl-containing oxindoles. In this transformation, silylcarboxylic acids play a dual role as a CO source and a nucleophile.

Phosphine-Free Aminocarbonylation Using Pd/DBU Catalyst: Carbonylative Coupling of Aryl Iodides and Amines

An improved carbonylation method allowing amide bond formation between aryl iodides and aromatic amines is presented. In contrast to usual methods based on Pd catalysis, this method does not require a phosphine ligand. The catalyst system simply employs bis(dibenzylideneacetone)palladium (0.5 mol %) and DBU (10 mol %). The method was applied to the synthesis of various aromatic amides from aryl iodides and amines, and was scaled to gram order synthesis under as low as 1 atm of carbon monoxide.

Palladium-Catalyzed Aminocarbonylation of Isoquinolines Utilizing Chloroform-COware Chemistry

The carbonyl group forms an integral part of several drug molecules and materials; hence, synthesis of carbonylated compounds remains an intriguing area of research for synthetic and medicinal chemists. Handling toxic CO gas has several limitations; thus, using safe and effective techniques for in or ex situ generation of carbon monoxide from nontoxic and cheap precursors is highly desirable. Among several precursors that have been explored for the generation of CO gas, chloroform can prove to be a promising CO surrogate due to its cost-effectiveness and ready availability. However, the one-pot chloroform-based carbonylation reaction requires strong basic conditions for hydrolysis of chloroform that may affect functional group tolerability of substrates and scale-up reactions. These limitations can be overcome by a two-chamber reactor (COware) that can be utilized for ex situ CO generation through hydrolysis of chloroform in one chamber and facilitating safe carbonylation reactions in another chamber under mild conditions. The versatility of this "Chloroform-COware" technique is explored through palladium-catalyzed aminocarbonylation of medicinally relevant heterocyclic cores, viz., isoquinoline and quinoline.

Replacement of Less-Preferred Dipolar Aprotic and Ethereal Solvents in Synthetic Organic Chemistry with More Sustainable Alternatives

Dipolar aprotic and ethereal solvents comprise just over 40% of all organic solvents utilized in synthetic organic, medicinal, and process chemistry. Unfortunately, many of the common "go-to" solvents are considered to be "less-preferable" for a number of environmental, health, and safety (EHS) reasons such as toxicity, mutagenicity, carcinogenicity, or for practical handling reasons such as flammability and volatility. Recent legislative changes have initiated the implementation of restrictions on the use of many of the commonly employed dipolar aprotic solvents such as dimethylformamide (DMF) and N-methyl-2-pyrrolidinone (NMP), and for ethers such as 1,4-dioxane. Thus, with growing legislative, EHS, and societal pressures, the need to identify and implement the use of alternative solvents that are greener, safer, and more sustainable has never been greater. Within this review, the ubiquitous nature of dipolar aprotic and ethereal solvents is discussed with respect to the physicochemical properties that have made them so appealing to synthetic chemists. An overview of the current legislative restrictions being imposed on the use of dipolar aprotic and ethereal solvents is discussed. A variety of alternative, safer, and more sustainable solvents that have garnered attention over the past decade are then examined, and case studies and examples where less-preferable solvents have been successfully replaced with a safer and more sustainable alternative are highlighted. Finally, a general overview and guidance for solvent selection and replacement are included in the Supporting Information of this review.

Highly Selective Synthesis of 6-Glyoxylamidoquinoline Derivatives via Palladium-Catalyzed Aminocarbonylation

The aminocarbonylation of 6-iodoquinoline has been investigated in the presence of large series of amine nucleophiles, providing an efficient synthetic route for producing various quinoline-6-carboxamide and quinoline-6-glyoxylamide derivatives. It was shown, after detailed optimization study, that the formation of amides and ketoamides is strongly influenced by the reaction conditions. Performing the reactions at 40 bar of carbon monoxide pressure in the presence of Pd(OAc)₂/2 PPh₃, the corresponding 2-ketocarboxamides were formed as major products (up to 63%). When the monodentate triphenylphosphine was replaced by the bidentate XantPhos, the quinoline-6-carboxamide derivatives were synthesized almost exclusively under atmospheric conditions (up to 98%). The isolation and characterization of the new carbonylated products of various structures were also accomplished. Furthermore, the structure of three new mono- and double-carbonylated compounds were unambiguously established by using a single-crystal XRD study.

Cobalt catalysed aminocarbonylation of thiols in batch and flow for the preparation of amides

The synthesis of amides from thiols through a cobalt-catalyzed aminocarbonylation is shown. After optimizing all the reaction parameters, the methodology makes possible the obtention of amides with variable yields, while competing reactions such as the formation of disulfides and ureas can be limited. The process works well with aromatic thiols with electron donating groups (EDG) whereas other thiols give reaction with lower yields. The previous process has been transferred and optimized into flow equipment, thus allowing using less CO in a safer way, and permitting the scaling up of the synthesis. Two drugs, moclobemide and itopride were prepared with this methodology, albeit only in the second case with good results. A mechanistic pathway is proposed.

Pd-Catalyzed Alkene Diamination Reactions with O-Benzoylhydroxylamine Electrophiles: Evidence Supporting a Pd(II/IV) Catalytic Cycle, the Role of 2,4-Pentanedione Derivatives as Ligands, and Expanded Substrate Scope

This article describes continued studies on Pd-catalyzed alkene diamination reactions between N-allylguanidines or ureas and O-benzoylhydroxylamine derivatives, which serve as N-centered electrophiles. The transformations generate cyclic guanidines and ureas bearing dialkylaminomethyl groups in moderate to good yield. We describe new mechanistic experiments that have led to a revised mechanistic hypothesis that involves a key oxidative addition of the electrophile to a Pd^II complex, followed by reductive elimination from Pd^IV to form the alkyl carbon-nitrogen bond. In addition, we demonstrate that acac, not phosphine, serves as a key ligand for palladium. Moreover, simple acac derivatives bearing substituted aryl groups outperform acac in the catalytic reactions, and phosphines inhibit catalysis in many cases. These discoveries have led to a significant expansion in the scope of this chemistry, which now allows for the coupling of a variety of cyclic amines, acyclic secondary amines, and primary amines. In addition, we also demonstrate that these new conditions allow for the use of amide nucleophiles, in addition to guanidines and ureas.

Site-Selective Cross-Coupling of Polyhalogenated Arenes and Heteroarenes with Identical Halogen Groups

Methods to functionalize arenes and heteroarenes in a site-selective manner are highly sought after for rapidly constructing value-added molecules of medicinal, agrochemical, and materials interest. One effective approach is the site-selective cross-coupling of polyhalogenated arenes bearing multiple, but identical, halogen groups. Such cross-coupling reactions have proven to be incredibly effective for site-selective functionalization. However, they also present formidable challenges due to the inherent similarities in the reactivities of the halogen substituents. In this Review, we discuss strategies for site-selective cross-couplings of polyhalogenated arenes and heteroarenes bearing identical halogens, beginning first with an overview of the reaction types that are more traditional in nature, such as electronically, sterically, and directing-group-controlled processes. Following these examples is a description of emerging strategies, which includes ligand- and additive/solvent-controlled reactions as well as photochemically initiated processes.

Advances in Visible-Light-Mediated Carbonylative Reactions via Carbon Monoxide (CO) Incorporation

The abundant and inexpensive carbon monoxide (CO) is widely exploited as a C1 source for the synthesis of both fine and bulk chemicals. In this context, photochemical carbonylation reactions have emerged as a powerful tool for the sustainable synthesis of carbonyl-containing compounds (esters, amides, ketones, etc.). This review aims at giving a general overview on visible light-promoted carbonylation reactions in the presence of metal (Palladium, Iridium, Cobalt, Ruthenium, Copper) and organocatalysts as well, highlighting the main features of the presented protocols and providing useful insights on the reaction mechanisms.

Metallaphotoredox catalysis with organic dyes

Here…comes the fun…Combination of metals and organic photocatalysts allows the practical invention of new methodologies!

Solvent Effects on the Selectivity of Palladium-Catalyzed Suzuki-Miyaura Couplings

The use of polar solvents MeCN or dimethylformamide (DMF) was previously shown to induce a selectivity switch in the Pd/P ^t Bu₃-catalyzed Suzuki-Miyaura coupling of chloroaryl triflates. This phenomenon was attributed to the ability of polar solvents to stabilize anionic transition states for oxidative addition. However, we demonstrate that selectivity in this reaction does not trend with solvent dielectic constant. Unlike MeCN and DMF, water, alcohols, and several polar aprotic solvents such as MeNO₂, acetone, and propylene carbonate provide the same selectivity as nonpolar solvents. These results indicate that the role of solvent on the selectivity of Suzuki-Miyaura couplings may be more complex than previously envisioned. Furthermore, this observation has the potential for synthetic value as it greatly broadens the scope of solvents that can be used for chloride-selective cross coupling of chloroaryl triflates.

Cobalt-catalyzed aminocarbonylation of (hetero)aryl halides promoted by visible light

The catalytic aminocarbonylation of (hetero)aryl halides is widely applied in the synthesis of amides but relies heavily on the use of precious metal catalysis. Herein, we report an aminocarbonylation of (hetero)aryl halides using a simple cobalt catalyst under visible light irradiation. The reaction extends to the use of (hetero)aryl chlorides and is successful with a broad range of amine nucleophiles. Mechanistic investigations are consistent with a reaction proceeding via intermolecular charge transfer involving a donor–acceptor complex of the substrate and cobaltate catalyst.

An aminocarbonylation of (hetero)aryl halides using a simple cobalt catalyst under visible light irradiation is presented.

Access to Aryl and Heteroaryl Trifluoromethyl Ketones from Aryl Bromides and Fluorosulfates with Stoichiometric CO

We report a sequential one-pot preparation of aromatic trifluoromethyl ketones starting from readily accessible aryl bromides and fluorosulfates, the latter easily prepared from the corresponding phenols. The methodology utilizes low pressure carbon monoxide generated ex situ from COgen to generate Weinreb amides as reactive intermediates that undergo monotrifluoromethylation affording the corresponding aromatic trifluoromethyl ketones (TFMKs) in good yields. The stoichiometric use of CO enables the possibility for accessing ¹³C-isotopically labeled TFMK by switching to the use of ¹³COgen.

Amide Synthesis by Nickel/Photoredox-Catalyzed Direct Carbamoylation of (Hetero)Aryl Bromides

Herein, we report a one‐electron strategy for catalytic amide synthesis that enables the direct carbamoylation of (hetero)aryl bromides. This radical cross‐coupling approach, which is based on the combination of nickel and photoredox catalysis, proceeds at ambient temperature and uses readily available dihydropyridines as precursors of carbamoyl radicals. The method's mild reaction conditions make it tolerant of sensitive‐functional‐group‐containing substrates and allow the installation of an amide scaffold within biologically relevant heterocycles. In addition, we installed amide functionalities bearing electron‐poor and sterically hindered amine moieties, which would be difficult to prepare with classical dehydrative condensation methods.

COtab: Expedient and Safe Setup for Pd-Catalyzed Carbonylation Chemistry

Bench-stable tablets (COtabs) have been developed for the rapid and safe production of carbon monoxide. The tablets can be made in less than 5 min without the use of a glovebox and only require a stock solution of an amine base to liberate a specific quantity of CO in a two-chamber system. The COtabs were tested in five different carbonylation reactions and provided similar yields compared to literature procedures. Finally, a gram-scale reaction was conducted, as well as ¹³C-isotope labeling of the anticancer drug, olaparib.

Hydroxyl-functionalized triazolylidene-based PEPPSI complexes: metallacycle formation effect on the Suzuki coupling reaction

We report the preparation and full characterization of a series of hydroxyl functionalized 1,2,3-triazolylidene-based PEPPSI complexes 2a-c and their catalytic application in the Suzuki cross coupling reaction of aryl chlorides/amides with boronic acids. Under basic reaction conditions, complexes 2a-c show a notable increase in their catalytic efficiency compared with two ether-wingtip functionalized PEPPSI analogues (3 and 4) and a commercially available NHC-Pd complex (5). The catalytic results suggest that deprotonation of the hydroxyl group in complexes 2a-c plays an important role in the overall process. Deprotonation of the alcohol moiety of complexes 2a-b with sodium tert-butoxide allows for the isolation of metallacycles 6a-b, which are proposed as the active species of cross coupling reactions.

Aminophosphine Palladium Pincer-Catalyzed Carbonylative Sonogashira and Suzuki-Miyaura Cross-Coupling with High Catalytic Turnovers

This work documents the first palladium pincer complex-catalyzed carbonylative Sonogashira (CS) and carbonylative Suzuki-Miyaura (CSM) cross-coupling. Compared to previous protocols, which employ hazardous and toxic solvents, the aminophosphine pincer complex {[C₆H₃-2,6-(NHP{piperidinyl}₂)₂]Pd(Cl)} (III) catalyzes both the cross-coupling reactions in propylene carbonate, an eco-friendly and sustainable polar aprotic solvent. Advantageously, employing III allows the CS cross-coupling to be carried out at a palladium loading of 10^-4 mol % and the CSM cross-coupling to be carried out at 10^-6 mol %, thus resulting in catalytic turnovers of 10⁵ and 10⁷, respectively. Relative comparison of the pincer complex with conventional palladium precursors Pd(OAc)₂ and PdCl₂(PPh₃)₂ shows the efficiency and robustness of the pincer complex in effecting higher catalytic activity at low palladium loadings.

Formates plus triazabicyclodecene (TBD): an efficient platform for non-gaseous carbonylation and unexpected hydrogenation

A highly efficient palladium-catalyzed TBD–formate system for carbonylation/hydrogenation was reported.

One-pot regioselective synthesis of substituted pyrazoles and isoxazoles in PEG-400/water medium by Cu-free nano-Pd catalyzed sequential acyl Sonogashira coupling–intramolecular cyclization

Catalyst efficacy of in situ generated Pd-nanoparticles in the regioselective one-pot synthesis of substituted pyrazoles and isoxazoles via sequential coupling-cyclization methodology in environmentally benign medium is described.

Enantiodivergent Pd-catalyzed C-C bond formation enabled through ligand parameterization

Despite the enormous potential for the use of stereospecific cross-coupling reactions to rationally manipulate the three-dimensional structure of organic molecules, the factors that control the transfer of stereochemistry in these reactions remain poorly understood. Here we report a mechanistic and synthetic investigation into the use of enantioenriched alkylboron nucleophiles in stereospecific Pd-catalyzed Suzuki cross-coupling reactions. By developing a suite of molecular descriptors of phosphine ligands, we could apply predictive statistical models to select or design distinct ligands that respectively promoted stereoinvertive and stereoretentive cross-coupling reactions. Stereodefined branched structures were thereby accessed through the predictable manipulation of absolute stereochemistry, and a general model for the mechanism of alkylboron transmetallation was proposed.