Upgrading carbon dioxide by incorporation into heterocycles

Highly efficient conversion of CO2 to cyclic carbonates with a binary catalyst system in a microreactor: intensification of “electrophile–nucleophile” synergistic effect

An intensification of the “electrophile–nucleophile” synergistic effect was achieved in a microreactor for the coupling reaction of CO₂ and epoxides mediated by the binary Al complex/ternary ammonium salt catalyst system. The microreactor technology is proven to be a powerful tool for the preparation of cyclic carbonates with an improved reaction rate and a wide substrate scope.

An intensification of the “electrophile–nucleophile” synergistic effect was achieved in a microreactor for the coupling reaction of CO₂ and epoxides mediated by the binary Al complex/ternary ammonium salt catalyst system.

Calix[4]pyrroles as macrocyclic organocatalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide

meso-Octamethylcalix[4]pyrrole worked as an organocatalyst for the conversion of epoxides and CO₂ into cyclic carbonates under solvent-free conditions.

Reactions of secondary propargylamines with heteroallenes for the synthesis of diverse heterocycles

This focused review aims to summarize recent developments in the processes involving additions of secondary propargylamines to various heteroallenes and subsequent transition metal-catalyzed or electrophile-mediated cyclizations.

Ce(iii)-Containing tungstotellurate(vi) with a sandwich structure: an efficient Lewis acid–base catalyst for the condensation cyclization of 1,3-diketones with hydrazines/hydrazides or diamines

A new Ce³⁺ modified Dawson-like polyoxometalate cluster was synthesized, which showed good Lewis acid and Lewis base activities in the condensation reaction.

Oxy-Difluoroalkylation of Allylamines with CO2 via Visible-Light Photoredox Catalysis

A selective oxy-difluoroalkylation of allylamines with carbon dioxide (CO₂) via visible-light photoredox catalysis is reported. These multicomponent reactions are efficient and environmentally friendly to generate a series of important 2-oxazolidinones with functionalized difluoroalkyl groups. The good functional group tolerance, broad substrate scope, easy scalability, mild reaction conditions, and facile functionalization of products provide great potential for application in organic synthesis and pharmaceutical chemistry.

Synthesis meets theory: Past, present and future of rational chemistry

Chemical synthesis has its roots in the empirical approach of alchemy. Nonetheless, the birth of the scientific method, the technical and technological advances (exploiting revolutionary discoveries in physics) and the improved management and sharing of growing databases greatly contributed to the evolution of chemistry from an esoteric ground into a mature scientific discipline during these last 400 years. Furthermore, thanks to the evolution of computational resources, platforms and media in the last 40 years, theoretical chemistry has added to the puzzle the final missing tile in the process of “rationalizing” chemistry. The use of mathematical models of chemical properties, behaviors and reactivities is nowadays ubiquitous in literature. Theoretical chemistry has been successful in the difficult task of complementing and explaining synthetic results and providing rigorous insights when these are otherwise unattainable by experiment. The first part of this review walks the reader through a concise historical overview on the evolution of the “model” in chemistry. Salient milestones have been highlighted and briefly discussed. The second part focuses more on the general description of recent state-of-the-art computational techniques currently used worldwide by chemists to produce synergistic models between theory and experiment. Each section is complemented by key-examples taken from the literature that illustrate the application of the technique discussed therein.

An Efficient and Versatile Lanthanum Heteroscorpionate Catalyst for Carbon Dioxide Fixation into Cyclic Carbonates

A new lanthanum heteroscorpionate complex has shown exceptional catalytic activity for the synthesis of cyclic carbonates from epoxides and carbon dioxide. This catalyst system also promotes the reaction of bio-based epoxides to give an important class of bis(cyclic carbonates) that can be further used for the production of bio-derived non-isocyanate polyurethanes. The catalytic process requires low catalyst loading and mild reaction conditions for the synthesis of a wide range of cyclic carbonates.

Betaine Catalysis for Hierarchical Reduction of CO2 with Amines and Hydrosilane To Form Formamides, Aminals, and Methylamines

An efficient, sustainable organocatalyst, glycine betaine, was developed for the reductive functionalization of CO₂ with amines and diphenylsilane. Methylamines and formamides were obtained in high yield by tuning the CO₂ pressure and reaction temperature. Based on identification of the key intermediate, that is, the aminal, an alternative mechanism for methylation involving the C⁰ silyl acetal and aminal is proposed. Furthermore, reducing the CO₂ amount afforded aminals with high yield and selectivity. Therefore, betaine catalysis affords products with a diversified energy content that is, formamides, aminals and methylamines, by hierarchical two-, four- and six-electron reduction, respectively, of CO₂ coupled with C-N bond formation.

Synthesis of Ureas from CO2

Ureas are an important class of bioactive organic compounds in organic chemistry and exist widely in natural products, agricultural pesticides, uron herbicides, pharmaceuticals. Even though urea itself has been synthesized from CO₂ and ammonia for a long time, the selective and efficient synthesis of substituted ureas is still challenging due to the difficulty of dehydration processes. Efficient and economic fixation of CO₂ is of great importance in solving the problems of resource shortages, environmental issues, global warming, etc. During recent decades, chemists have developed different catalytic systems to synthesize ureas from CO₂ and amines. Herein, we focus on catalytic synthesis of ureas using CO₂ and amines.

A Simple Zinc Catalyst for Carbamate Synthesis Directly from CO2

Several zinc salts were employed as catalysts for the synthesis of carbamates directly from aromatic amines, CO₂ , and silicate esters. Zn(OAc)₂ offered the best performance among the salts tested. The addition of an N-donor ligand such as 1,10-phenanthroline increased the yield. The best catalytic performance of Zn(OAc)₂ can be explained by carboxylate-assisted proton activation. The interaction between the substrate and the catalyst can be observed by chemical shifts in ¹ H and ¹⁵ N NMR spectra. Isocyanate was a key intermediate, which was generated from amine and CO₂ . Silicate ester was finally converted to siloxane, which was determined by ²⁹ Si NMR. The commercially available catalyst system could be reused. The yield of isolated carbamate could reach up to 96 % with various substrates, and the catalytic reaction was amine-selective in the presence of other functional groups.

Photochemical Carboxylation of Activated C(sp3 )-H Bonds with CO2

From ugly duckling to beautiful C1: Although CO₂ may represent an ideal C1 source, it is challenging to use it as a raw material and direct carboxylation with CO₂ has mainly been confined to highly reactive species. However, recent significant breakthroughs have been made in photochemical carboxylation of challenging, un-acidic, C(sp³ )-H bonds, including benzylic, allylic and amine C-H bonds.

Recyclable Single-Component Rare-Earth Metal Catalysts for Cycloaddition of CO2 and Epoxides at Atmospheric Pressure

Ionic rare-earth metal complexes 1-4 bearing an imidazolium cation were synthesized, which, as single-component catalysts, showed good activity in catalyzing cyclic carbonate synthesis from epoxides and CO₂. In the presence of 0.2 mol % catalyst, monosubstituted epoxides bearing different functional groups were converted into cyclic carbonates in 60-97% yields under atmospheric pressure. In addition, bulky/internal epoxides with low reactivity yielded cyclic carbonates in 40-95% yields. More importantly, the readily available samarium complex 2 was reused for six successive cycles without any significant loss in its catalytic activity. This is the first recyclable rare-earth metal-based catalyst in cyclic carbonate synthesis.

Aluminum-Mediated Formation of Cyclic Carbonates: Benchmarking Catalytic Performance Metrics

We report a comparative study on the activity of a series of fifteen binary catalysts derived from various reported aluminum-based complexes. A benchmarking of their initial rates in the coupling of various terminal and internal epoxides in the presence of three different nucleophilic additives was carried out, providing for the first time a useful comparison of activity metrics in the area of cyclic organic carbonate formation. These investigations provide a useful framework for how to realistically valorize relative reactivities and which features are important when considering the ideal operational window of each binary catalyst system.

Carbocation/Polyol Systems as Efficient Organic Catalysts for the Preparation of Cyclic Carbonates

Carbocation/polyol systems are shown to be highly efficient catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide at 50 °C and 5 MPa CO₂ pressure. The best activity was shown by the combination of crystal violet and 1,1'-bi-2-naphthol (BINOL), which could be recycled five times with no loss of activity. The presence of specific interactions between the amino groups of the carbocation and the hydroxyl protons was confirmed by NMR experiments. The Job plots for the crystal violet iodide/BINOL and brilliant green iodide/BINOL systems showed that the catalytic systems consist of one molecule of the carbocation and one molecule of BINOL. Mechanistic studies using a deuterated epoxide indicate that there was some loss of epoxide stereochemistry during the reaction, but predominant retention of stereochemistry is observed. On this basis, a catalytic cycle is proposed.

In Situ Generated Zinc(II) Catalyst for Incorporation of CO2 into 2-Oxazolidinones with Propargylic Amines at Atmospheric Pressure

Incorporation of CO₂ into heterocyclic compounds (i.e., 2-oxazolidinones) under mild conditions, especially at atmospheric pressure still remains challenging. The mononuclear Zn^II complex ZnCl₂ (TBD)₂ , where TBD=1,5,7-triazabicyclo[4.4.0]dec-5-ene, in this study was demonstrated as a robust catalyst for the carboxylative cyclization of propargylic amines with CO₂ to exclusively afford various 2-oxazolidinones in excellent yields. Notably, the Zn^II catalytic species is readily generated in situ from ZnCl₂ and TBD without pre-preparation and further isolation. Such a CO₂ fixation protocol could proceed smoothly under atmospheric pressure at mild temperature in an atom economic and environmentally benign manner. ¹³ C NMR and control experiments were performed to explore the possible interaction between Zn^II and the carbon-carbon triple bond of propargylic amine. The dual catalytic role of the Zn catalyst to enhance O-nucleophilicity of the carbamate anion intermediate and activate the carbon-carbon triple bond is proposed based on mechanistic investigations.

Cyanuric Acid-Based Organocatalyst for Utilization of Carbon Dioxide at Atmospheric Pressure

A organocatalytic system based on economical and readily available cyanuric acid has been developed for the synthesis of 2-oxazolidinones and quinazoline-2,4(1H,3H)-diones from propargylamines and 2-aminobenzonitriles under atmospheric pressure carbon dioxide. Notably, a low concentration of carbon dioxide in air was directly converted into 2-oxazolidinone in excellent yields without an external base. Through mechanistic investigation by in situ FTIR spectroscopy, cyanuric acid was demonstrated to be an efficient catalyst for carbon dioxide fixation.

Computationally Designed 1,2,4-Triazolylidene-Derived N-Heterocyclic Olefins for CO2 Capture, Activation, and Storage

In this article, triazolylidene-derived N-heterocyclic olefins (trNHOs) are designed using computational quantum tools, and their potential to promote CO2 sequestration is tested and discussed in detail. The low barrier heights related to the trNHO-mediated process indicate that the tailored compounds are very promising for fast CO2 sequestration. The systematic analysis of the presence of distinct substitutes at different N positions of the trNHO ring allows us to rationalize their effect on the carboxylation process and reveal the best N-substituted trNHO systems for CO2 sequestration and improved trNHO carboxylates for faster CO2 capture/release.

Silver(I)-Promoted Cascade Reaction of Propargylic Alcohols, Carbon Dioxide, and Vicinal Diols: Thermodynamically Favorable Route to Cyclic Carbonates

A silver(I)-promoted cascade reaction was developed for the synthesis of cyclic carbonates from terminal propargylic alcohols, carbon dioxide, and vicinal diols. Compared with direct condensation of vicinal diols with CO₂, this protocol provides a thermodynamically favorable route to cyclic carbonates and α-hydroxyl ketones in excellent yields (up to 97%) without the additional dehydration step. Such a cascade procedure proceeds presumably through initial reaction of propargylic alcohol with CO₂ and subsequent nucleophilic attack of vicinal alcohol on in situ-formed α-alkylidene cyclic carbonate, resulting in successive generation of α-alkylidene cyclic carbonate, unsymmetrical β-oxoalkyl carbonate, cyclic carbonate, and α-hydroxyl ketone.