Divergent synthesis of carbamates and N-methyl carbamates from dimethyl carbonate and nitroarenes with Mo(CO)6 as a multiple promoter

Dialkyl carbonates are green and versatile reagents that can be used in alkylation and alkoxycarbonylation reactions. Herein, we disclosed a reductive methoxycarbonylation of aromatic nitro compounds with dimethyl carbonate for the construction of diverse carbamates and N-methyl carbamates. Using Mo(CO)6 as a multiple promoter, different nitroarenes were smoothly transformed into the corresponding carbamates in yields between 27 and 94% using DMC as both solvent and reagent. It is worth noting that the choice of different bases allowed the desired products to be controlled: K3PO4 favoured the formation of carbamates as the primary product, whereas DBU facilitated the formation of N-methyl carbamates as the main product.

Direct synthesis of phthalimides via palladium-catalysed double carbonylation of o-dihaloarenes with nitroarenes

The direct carbonylation of readily available nitro compounds is more attractive and straightforward than the use of traditional amines as nucleophiles. Herein, a practical palladium-catalysed double carbonylation of nitroarenes with o-dihaloarenes has been developed for the construction of various N-aryl phthalimides. Key to the success of this transformation is the use of Mo(CO)6, which acts as both a reducing agent and a solid carbonyl source. A wide range of nitroarenes and o-dihaloarenes as well as o-iodobenzoic acids reacted smoothly to give phthalimides in 27-94% yields.

Nickel Catalyzed Carbonylation/Carboxylation Sequence via Double CO2 Incorporation

A carbonylation-carboxylation synthetic sequence, via double CO2 fixation, is described. The productive merger of a Ni-catalyzed cross-electrophile coupling manifold, with the use of AlCl3, triggered a cascade reaction with the formation of three consecutive C-C bonds in a single operation. This strategy traces an unprecedented synthetic route to ketones under Lewis acid assisted carbon dioxide valorization. Computational insights revealed a unique double function of AlCl3, and labeling (13CO2) experiments validate the genuine incorporation of CO2 in both functional groups.

Regioselective hydroesterification of alkenes and alkenylphenols utilizing CO2 and hydrosilane

As an important and attractive C1 building block, the diversified exploitation of CO₂ in chemical transformations possesses significant research and application value. Herein, an effective palladium-catalyzed intermolecular hydroesterification of a wide range of alkenes with CO₂ and PMHS is described, successfully generating diverse esters with up to 98% yield and up to 100% linear-selectivity. In addition, the palladium-catalyzed intramolecular hydroesterification of alkenylphenols with CO₂ and PMHS is also developed to construct a variety of 3-substituted-benzofuran-2(3H)-ones with up to 89% yield under mild conditions. In both systems, CO₂ functions as an ideal CO source with the assistance of PMHS, thus smoothly participating in a series of alkoxycarbonylation processes.

In Situ-Generated CuI Catalytic System for Oxidative N-Formylation of N-Heterocycles and Acyclic Amines with Methanol

The development of a sustainable and simple catalytic system for N-formylation of N-heterocycles with methanol by direct coupling remains a challenge, owing to many competing side reactions, given the sensitivity of N-heterocycles to many catalytic oxidation or dehydrogenation systems. This work concerns the development of an in situ-generated Cu^I catalytic system for oxidative N-formylation of N-heterocycles with methanol that is based on the case study of a more typical 1,2,3,4-tetrahydroquinoline as substrate. Aside from N-heterocycles, some acyclic amines are also transformed into the corresponding N-formamides in moderate yields. Furthermore, a probable reaction mechanism and reaction pathway are proposed and extension of work based on some findings leads to a demonstration that the formed ⋅O₂ ^- and ⋅OOH radicals in the catalytic system is related to the formation of undesired tar-like products.

PNP-type ligands enabled copper-catalyzed N-formylation of amines with CO2 in the presence of silanes

The sustainable catalytic transformation of carbon dioxide into valuable fine chemicals with high efficiency is a global challenge as although CO₂ is an abundant, nontoxic, and sustainable carbon feedstock it is also the most important factor behind the Greenhouse Effect. We describe herein a PNP-type ligand-enabled copper-catalyzed N-formylation of amines utilizing CO₂ as the building block in the presence of hydrosilane as the reductant. Our current protocol featured newly synthesized PNP-type ligands with broad substrate scope under mild reaction conditions.

A practical concept for catalytic carbonylations using carbon dioxide

The rise of CO₂ in atmosphere is considered as the major reason for global warming. Therefore, CO₂ utilization has attracted more and more attention. Among those, using CO₂ as C1-feedstock for the chemical industry provides a solution. Here we show a two-step cascade process to perform catalytic carbonylations of olefins, alkynes, and aryl halides utilizing CO₂ and H₂. For the first step, a novel heterogeneous copper 10Cu@SiO₂-PHM catalyst exhibits high selectivity (≥98%) and decent conversion (27%) in generating CO from reducing CO₂ with H₂. The generated CO is directly utilized without further purification in industrially important carbonylation reactions: hydroformylation, alkoxycarbonylation, and aminocarbonylation. Notably, various aldehydes, (unsaturated) esters and amides are obtained in high yields and chemo-/regio-selectivities at low temperature under ambient pressure. Our approach is of interest for continuous syntheses in drug discovery and organic synthesis to produce building blocks on reasonable scale utilizing CO₂.

Copper-Catalyzed Substrate-Controlled Carbonylative Synthesis of α-Keto Amides and Amides from Alkyl Halides

Controllable production of α-keto amides and amides from the same substrates is an attractive goal in the field of transition-metal-catalyzed (double-)carbonylation. Herein, a novel copper-catalyzed highly selective double carbonylation of alkyl bromides has been developed. Moderate to good yields of α-keto amides were obtained as the only products. In the case of alkyl iodides, double- and mono-carbonylation can be achieved controllably under different conditions.

Photocatalytic synthesis of tetra-substituted furans promoted by carbon dioxide

A CO2-promoted transition metal-free photocatalytic synthesis of tetra-substituted furan derivatives from 1,3-diketones as the only starting material.

Electrochemical Approaches to Carbonylative Coupling Reactions

The carbonylation reaction is an effective way to introduce CO or other carbonyl groups into organic compounds, and widely used in the preparation of aldehydes, ketones, amides, and esters. The replacement of conventional reaction approaches by greener electrochemical methods is appealing with great synthetic potential as well as inherent safety, owing to the avoidance of external oxidants or reductants and a more facile control in product selectivity. In this minireview, we give a summary of the recent development of carbonylation reactions via the electrochemical approach.

Alkali-modified heterogeneous Pd-catalyzed synthesis of acids, amides and esters from aryl halides using formic acid as the CO precursor

To establish an environmentally friendly green chemical process, we minimized and resolved a significant proportion of waste and hazards associated with conventional organic acids and molecular gases, such as carbon monoxide (CO). Herein, we report a facile and milder reaction procedure, using low temperatures/pressures and shorter reaction time for the carboxyl- and carbonylation of diverse arrays of aryl halides over a newly developed cationic Lewis-acid promoted Pd/Co₃O₄ catalyst. Furthermore, the reaction proceeded in the absence of acid co-catalysts, and anhydrides for CO release. Catalyst reusability was achieved via scalable, safer, and practical reactions that provided moderate to high yields, paving the way for developing a novel environmentally benign method for synthesizing carboxylic acids, amides, and esters.

To establish an environmentally friendly green chemical process, we minimized and resolved a significant proportion of waste and hazards associated with conventional organic acids and molecular gases, such as carbon monoxide (CO).

Enantioselective CO2 Fixation Via a Heck-Coupling/Carboxylation Cascade Catalyzed by Nickel

A novel asymmetric nickel-based procedure has been developed in which CO₂ fixation is achieved as a second step of a truncated Heck coupling. For this, a new chiral ligand has been prepared and shown to achieve enantiomeric excesses up to 99 %. The overall process efficiently furnishes chiral 2,3-dihydrobenzofuran-3-ylacetic acids, an important class of bioactive products, from easy to prepare starting materials. A combined experimental and computational effort revealed the key steps of the catalytic cycle and suggested the unexpected participation of Ni(I) species in the coupling event.

Efficient Palladium-Catalyzed Carbonylation of 1,3-Dienes: Selective Synthesis of Adipates and Other Aliphatic Diesters

The dicarbonylation of 1,3‐butadiene to adipic acid derivatives offers the potential for a more cost‐efficient and environmentally benign industrial process. However, the complex reaction network of regioisomeric carbonylation and isomerization pathways, make a selective and direct transformation particularly difficult. Here, we report surprising solvent effects on this palladium‐catalysed process in the presence of 1,2‐bis‐di‐tert‐butylphosphin‐oxylene (dtbpx) ligands, which allow adipate diester formation from 1,3‐butadiene, carbon monoxide, and methanol with 97 % selectivity and 100 % atom‐economy under scalable conditions. Under optimal conditions a variety of di‐ and triesters from 1,2‐ and 1,3‐dienes can be obtained in good to excellent yields.

Recyclable Oxofluorovanadate-Catalyzed Formylation of Amines by Reductive Functionalization of CO2 with Hydrosilanes

An efficient method has been developed for the reductive amination of CO₂ by using readily available and recyclable oxofluorovanadates as catalysts. Various amines are transformed into the desired N-formylated products in moderate to excellent yields at room temperature in the presence of phenylsilane. Mechanistic studies based on in situ infrared spectroscopy suggest a reaction pathway initiated through F-Si interactions. The activated phenylsilane allows for CO₂ insertion to produce phenylsilyl formate, which undergoes attack by the amine to generate the target product.

Pd-Catalyzed C(sp2 )-H Alkoxycarbonylation of Phenethyl- and Benzylamines with Chloroformates as CO Surrogates

The site-selective functionalization of C-H bonds within a complex molecule remains a challenging task of capital synthetic importance. Herein, an unprecedented Pd-catalyzed C(sp² )-H alkoxycarbonylation of phenylalanine derivatives and other amines featuring picolinamide as the directing group (DG) is reported. This oxidative coupling is distinguished by its scalability, operational simplicity, and avoids the use of toxic carbon monoxide as the C₁ source. Remarkably, the easy cleavage of the DG enables the efficient assembly of isoindolinone compounds. Density Functional Theory calculations support a Pd^II /Pd^IV catalytic cycle.

Palladium-catalyzed directing group assisted and regioselectivity reversed cyclocarbonylation of arylallenes with 2-iodoanilines

A palladium-catalyzed regioselective cyclocarbonylation of N-(2-pyridyl)sulfonyl (N-SO₂Py)-2-iodoanilines with allenes was developed. The regioselectivity of arylallenes was reversed. Control experiments and DFT calculations were performed to understand the reaction details.

Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

A variety of chromone fused cyclopentanones are efficiently generated in good to high yields via palladium-catalyzed [2 + 2 + 1] annulation, in which cyclopropenone was utilized for the first time as the sole CO surrogate in the carbonylation process.

Direct N-formylation of nitroarenes with CO2

Herein we describe a straightforward N-formylation of nitroarenes with CO₂ to access N-aryl formamides exclusively in the presence of iron and hydrosilane as additives. This protocol showcases a good tolerance of a wide range of nitroarenes and nitroheteroarenes.

CO2 = CO + [O]: recent advances in carbonylation of C–H bonds with CO2

Carbon dioxide (CO₂) is an ideal one-carbon source owing to its nontoxicity, abundance, availability, and recyclability.

Palladium-catalyzed carbonylations of highly substituted olefins using CO-surrogates

CO surrogate chemistry: General protocols for alkoxycarbonylations of highly substituted olefins with paraformaldehyde and methyl formate are reported, allowing the performance of carbonylation reactions in all labs and for all kinds of substrates.

Photocarboxylation of Benzylic C-H Bonds

The carboxylation of sp³-hybridized C–H bonds with CO₂ is a challenging transformation. Herein, we report a visible-light-mediated carboxylation of benzylic C–H bonds with CO₂ into 2-arylpropionic acids under metal-free conditions. Photo-oxidized triisopropylsilanethiol was used as the hydrogen atom transfer catalyst to afford a benzylic radical that accepts an electron from the reduced form of 2,3,4,6-tetra(9H-carbazol-9-yl)-5-(1-phenylethyl)benzonitrile generated in situ. The resulting benzylic carbanion reacts with CO₂ to generate the corresponding carboxylic acid after protonation. The reaction proceeded without the addition of any sacrificial electron donor, electron acceptor or stoichiometric additives. Moderate to good yields of the desired products were obtained in a broad substrate scope. Several drugs were successfully synthesized using the novel strategy.

Integrative Photoreduction of CO2 with Subsequent Carbonylation: Photocatalysis for Reductive Functionalization of CO2

Efficient conversion of CO₂ into fuels and chemicals with solar energy would be promising, but also faces great challenge. In this context, we describe the photoreductive functionalization of CO₂ to construct new C-C, C-N, and C-O bonds through the respective Pd-catalyzed Suzuki carbonylation, aminocarbonylation, and alkoxycarbonylation of aryl iodides with CO in situ generated through the photoreduction of CO₂ . This protocol opens up an alternative avenue for CO₂ utilization by harnessing solar energy.

Lactamization of sp2 C–H bonds with CO2 under transition-metal-free and redox-neutral conditions: a computational mechanistic study

Bases play the primary role in Stages (I) and (III). CO₂ serves as an atomic oxidant [O] acceptor in Stage (II).