Recent advances in fixation of CO2 into organic carbamates through multicomponent reaction strategies

The Versatile and Strategic O-Carbamate Directed Metalation Group in the Synthesis of Aromatic Molecules: An Update

The aryl O-carbamate (ArOAm) group is among the strongest of the directed metalation groups (DMGs) in directed ortho metalation (DoM) chemistry, especially in the form Ar-OCONEt2. Since the last comprehensive review of metalation chemistry involving ArOAms (published more than 30 years ago), the field has expanded significantly. For example, it now encompasses new substrates, solvent systems, and metalating agents, while conditions have been developed enabling metalation of ArOAm to be conducted in a green and sustainable manner. The ArOAm group has also proven to be effective in the anionic ortho-Fries (AoF) rearrangement, Directed remote metalation (DreM), iterative DoM sequences, and DoM-halogen dance (HalD) synthetic strategies and has been transformed into a diverse range of functionalities and coupled with various groups through a range of cross-coupling (CC) strategies. Of ultimate value, the ArOAm group has demonstrated utility in the synthesis of a diverse range of bioactive and polycyclic aromatic compounds for various applications.

Macrocyclization of carbon dioxide with 3-triflyloxybenzynes and tetrahydrofuran: straightforward access to 14-membered macrolactones

A novel [2+2+5+5] macrocyclization of carbon dioxide with 3-triflyloxybenzynes and tetrahydrofuran has been disclosed for the first time under transition metal-free conditions. The reaction provides a facile method for the synthesis of a rare type of 14-membered macrocyclic lactone, which is potentially useful but difficult to access by existing methods.

Silver-Catalyzed Coupling of Ethynylbenziodoxolones with CO2 and Amines to Afford O-β-Oxoalkyl Carbamates

A novel three-component coupling reaction of ethynylbenziodoxolones (EBXs) with CO2 and amines has been achieved via silver catalysis, thereby providing an efficient method for the construction of a range of structurally diverse and valuable O-β-oxoalkyl carbamates. The transformation proceeds under mild reaction conditions and exhibits a wide substrate scope and good functional group compatibility. In addition, this strategy could be extended to the synthesis of α-acyloxyketones using carboxylic acids as the nucleophiles to react with EBXs.

Nanostructured electrocatalysts for organic synthetic transformations

Organic chemists have made and are still making enormous efforts toward the development of novel green catalytic synthesis. The necessity arises from the imperative of safeguarding human health and the environment, while ensuring efficient and sustainable chemical production. Within this context, electrocatalysis provides a framework for the design of new organic reactions under mild conditions. Undoubtedly, nanostructured materials are under the spotlight as the most popular and in most cases efficient platforms for advanced organic electrosynthesis. This Minireview focuses on the recent developments in the use of nanostructured electrocatalysts, highlighting the correlation between their chemical structures and resulting catalytic abilities, and pointing to future perspectives for their application in cutting-edge areas.

How To Get Isocyanate?

Isocyanate, a pivotal chemical intermediate to synthesize polyurethane with widespread applications in household appliances, automobiles, and construction, is predominantly produced via the phosgene process, which currently holds a paramount status in industrial isocyanate production. Nonetheless, concerns arise from the toxicity of phosgene and the corrosiveness of hydrogen chloride, posing safety hazards. The synthesis of isocyanate using nonphosgene methods represents a promising avenue for future development. This article primarily focuses on the nonphosgene approach, which involves the formation of carbamate through the reaction of nitro-amino compounds with carbon monoxide, dimethyl carbonate, and urea, among other reagents, subsequently leading to the thermal decomposition of carbamate to get isocyanate. This paper emphasizes the progress in catalyst development during the carbamate decomposition process. Single-component metal catalysts, particularly zinc, exhibit advantages such as high activity, cost-effectiveness, and compatibility with a wide range of substrates. Composite catalysts enhance isocyanate yield by introducing a second component to adjust the active metal composition. The central research direction aims to optimize catalyst adaptation to reaction conditions, including temperature, pressure, time, and solvent, to achieve high raw material conversion and product yield.

Cu-Catalyzed Asymmetric Dicarboxylation of 1,3-Dienes with CO2

Dicarboxylic acids and derivatives are important building blocks in organic synthesis, biochemistry, and the polymer industry. Although catalytic dicarboxylation with CO2 represents a straightforward and sustainable route to dicarboxylic acids, it is still highly challenging and limited to generation of achiral or racemic dicarboxylic acids. To date, catalytic asymmetric dicarboxylation with CO2 to give chiral dicarboxylic acids has not been reported. Herein, we report the first asymmetric dicarboxylation of 1,3-dienes with CO2 via Cu catalysis. This strategy provides an efficient and environmentally benign route to chiral dicarboxylic acids with high regio-, chemo-, and enantioselectivities. The copper self-relay catalysis, that is, Cu-catalyzed boracarboxylation of 1,3-dienes to give carboxylated allyl boronic ester intermediates and subsequent carboxylation of C-B bonds to give dicarboxylates, is key to the success of this dicarboxylation. Moreover, this protocol exhibits broad substrate scope, good functional group tolerance, easy product derivatizations, and facile synthesis of chiral liquid crystalline polyester and drug-like scaffolds.

Perfluoroalkyl-Decorated Noble-Metal-Free MOFs for the Highly Efficient One-Pot Four-Component Coupling between Aldehydes, Amines, Alkynes, and Flue Gas CO2

The non-noble-metal catalysed-multicomponent reactions between flue gas CO2 and cheap industrial raw stocks into high value-added fine chemicals is a promising manner for the ideal CO2 utilization route. To achieve this, the key fundamental challenge is the rational development of highly efficient and facile reaction pathway while establishing compatible catalytic system. Herein, through the stepwise solvent-assisted linker installation, post-synthetic fluorination and metalation, we report the construction of a series of perfluoroalkyl-decorated noble-metal-free metal-organic frameworks (MOFs) PCN-(BPY-CuI)-(TPDC-Fx ) [BPY=2,2'-bipyridine-5,5'-dicarboxylate, TPDC-NH2 =2'-amino-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid] that can catalyze the one-pot four-component reaction between alkyne, aldehyde, amine and flue gas CO2 for the preparation of 2-oxazolidinones. Such assembly endows the MOFs with superhydrophobic microenvironment, superior water resistance and highly stable catalytic site, leading to 21 times higher turnover numbers than that of homogeneous counterparts. Mechanism investigation implied that the substrates can be efficiently enriched by the MOF wall and then the adsorbed amine species act as an extrinsic binding site towards dilute CO2 through their strong preferential formation to carbamate acid. Moreover, density functional theory calculations suggest the tetrahedral geometry of Cu in MOF offers special resistance towards amine poisoning, thus maintaining its high efficiency during the catalytic process.

Continuous Synthesis of Carbamates from CO2 and Amines

We present a novel approach for the continuous preparation of carbamates. The simple yet fast synthetic route relies on directly utilizing carbon dioxide and, in contrast with the literature-known methods, only employs 1,8-diazabicyclo[5.4.0]undec-7-ene as an additive. The applicable amines' diversity offers considerable flexibility to the synthetic protocol. Additionally, the continuous method's applicability significantly decreases the reaction time typically required for CO2-based carbamate synthesis and allows for straightforward and precise gas introduction. The mild reaction conditions and omission of the need for column chromatography render the process less time-demanding and environmentally more benign, providing the desired compounds in yields of 45 to 92%. Moreover, the modified procedure can potentially be applied in the selective synthesis of oxazolidinones from aziridines.

C1 functionalization of imidazo heterocycles via carbon dioxide fixation

Utilizing CO2 as a one-carbon building block in the preparation of high-value chemical entities is a cornerstone of modern organic synthesis. Herein, we exemplify this strategy through a mild, one-pot methodology that gives rapid access to N-heteroaryl substituted 6-, 8- and 9-membered carbamates via CO2 fixation.

Direct access to carbamates via acylation of arylamines with dialkyl azodicarboxylates under metal-free conditions

A novel C-N coupling of various arylamines with dialkyl azodicarboxylates under metal-free conditions for the rapid assembly of carbamates has been achieved. This established protocol features mild reaction conditions, simple operation, broad substrate scope, moderate to excellent yields and good tolerance of functional groups. Moreover, the potential synthetic utility of products was exemplified by a series of intriguing chemical operations.

Dual Nickel Photocatalysis for O-Aryl Carbamate Synthesis from Carbon Dioxide

We report the use of dual nickel photocatalysis in the synthesis of O-aryl carbamates from aryl iodides or bromides, amines, and carbon dioxide. The reaction proceeded in visible light, at ambient carbon dioxide pressure, and without stoichiometric activating reagents. Mechanistic analysis is consistent with a Ni(I-III) cycle, where the active species is generated by the photocatalyst. The rate-limiting steps were the photocatalyst-mediated reduction of Ni(II) to Ni(I) and subsequent oxidative addition of the aryl halide. The physical properties of the photocatalyst were critical for promoting formation of O-aryl carbamates over various byproducts. Nine new phthalonitrile photocatalysts were synthesized, which exhibited properties that were vital to achieve high selectivity and activity.

Photoredox-catalyzed coupling of aryl sulfonium salts with CO2 and amines to access O-aryl carbamates

An efficient photoredox-catalyzed three-component coupling reaction of aryl sulfonium salts, carbon dioxide and amines has been developed for the first time. This reaction provides a new strategy for the synthesis of a range of valuable O-aryl carbamates from readily available arenes via a site-selective thianthrenation/carbamoyloxylation two-step process. Mild conditions, broad substrate scope and good functional group tolerance are the features of the transformation. The synthetic utility of the method was demonstrated by the late-stage modification of bioactive molecules and pharmaceuticals.

Palladium-Catalyzed Reductive Formylation of Aryl Iodides with CO2 under Mild Conditions

A palladium-catalyzed reductive formylation of aryl iodides with carbon dioxide as the carbonyl source under mild reaction conditions was realized by using a combination of Pd(PCy₃)₂Cl₂ and di-2-pyridyl ketone as the catalyst and phenylsilane as the reductive reagent, leading to a variety of aromatic aldehydes in moderate to excellent yields. The protocol features wide substrate scope, good functional group tolerance, and simple operation.

Palladium-Catalyzed Carbonylation of Aryl Bromides with Carbon Dioxide To Access Aryl Carboxylic Acids under Mild Conditions

A palladium-catalyzed direct carbonylation of aryl bromides with carbon dioxide as the carbonyl source has been developed by using Pd(dba)₂/DPEPhos as the catalyst under mild reaction conditions, providing an efficient route to a variety of aryl carboxylic acids in moderate to high yields. The methods have many advantages such as the use of a simple palladium catalyst system, wide substrate scope, good functional group tolerance, high yields, and easy scalability.

Electroreductive Ring-Opening Carboxylation of Cycloketone Oxime Esters with Carbon Dioxide

Electroreductive ring-opening carboxylation of cycloketone oxime esters with atmospheric carbon dioxide is reported. This reaction proceeded under simple constant current conditions in an undivided cell using glassy carbon as the cathode and magnesium as the sacrificial anode, providing substituted γ- and δ-cyanocarboxylic acids in moderate to good yields. Electrochemically generated cyanoalkyl radicals and cyanoalkyl anion are proposed as the key intermediates.

Direct and Selective Electrocarboxylation of Styrene Oxides with CO2 for Accessing β-Hydroxy Acids

Highly selective and direct electroreductive ring-opening carboxylation of epoxides with CO2 in an undivided cell is reported. This reaction shows broad substrate scopes within styrene oxides under mild conditions, providing practical and scalable access to important synthetic intermediate β-hydroxy acids. Mechanistic studies show that CO2 functions not only as a carboxylative reagent in this reaction but also as a promoter to enable efficient and chemoselective transformation of epoxides under additive-free electrochemical conditions. Cathodically generated α-radical and α-carbanion intermediates lead to the regioselective formation of α-carboxylation products.