Cycloaddition of Aziridine with CO2/CS2 Catalyzed by Amidato Divalent Lanthanide Complexes

Fe(II)-Iminopyridine Catalyst for the Regioselective Synthesis of Oxazolidinones Using Carbon Dioxide

This study presents the application of a novel Fe-iminopyridine catalyst for the regioselective synthesis of oxazolidinones from carbon dioxide and aziridines. Our findings demonstrate that the Fe-iminopyridine catalyst containing imidazole functional group offers promising efficiency and facilitates a sustainable approach to green chemical synthesis at 50 °C and 10 bar CO2 pressure in a single-component Fe catalyst system. Various aziridines with carboxylic acid-derived substituents were transformed into 5-carbonyl substituted oxazolidinone products. The regioselective synthesis of oxazolidinones followed by the reduction enhances their utility for the pharmaceutically valuable compounds.

Chemical fixation of CO2/CS2 to access iodoallenyl oxazolidinones and allenyl thiazolidine-thiones

Constructing heterocyclic compounds by chemical fixation of CO2/CS2 as a C1 building block is a promising approach. An efficient and environmentally friendly synthetic approach has been developed using CO2/CS2 to prepare complicated allenyl heterocycles with high yields and diastereoselectivities in a metal-free manner under mild conditions. NIS promoted CO2 fixation and the cyclization reaction by exclusive 1,4-syn-addition of 1,3-enynes rather than 1,2-addition or 3,4-addition, while CS2 participated in unique 1,4-syn-hydrothiolation of 1,3-enynes to afford allenyl heterocycles with different reaction patterns.

Metal Hydrogen-Bonded Organic Frameworks as Open Lewis Acid Catalysts for Two Types of CO2 Transformations

Efficient and multiple CO2 utilization into high-value-added chemicals holds significant importance in carbon neutrality and industry production. However, most catalysis systems generally exhibit only one type of CO2 transformation with the efficiency to be improved. The restricted abundance of active catalytic sites or an inefficient utilization rate of these sites results in the constraint. Consequently, we designed and constructed two metal hydrogen-bonded organic frameworks (M-HOFs) {[M3(L3-)2(H2O)10]·2H2O}n (M = Co (1), Ni (2); L = 1-(4-carboxyphenyl)-1H-pyrazole-3,5-dicarboxylic acid) in this research. 1 and 2 are well-characterized, and both show excellent stability. The networks connected by multiple hydrogen bonds enhance the structural flexibility and create accessible Lewis acidic sites, promoting interactions between the substrates and catalytic centers. This enhancement facilitates efficient catalysis for two types of CO2 transformations, encompassing both cycloaddition reactions with epoxides and aziridines to afford cyclic carbonates and oxazolidinones. The catalytic activities (TON/TOF) are superior compared with those of most other catalysts. These heterogeneous catalysts still exhibited high performance after being reused several times. Mechanistic studies indicated intense interactions between the metal sites and substrates, demonstrating the reason for efficient catalysis. This marks the first instance on M-HOFs efficiently catalyzing two types of CO2 conversions, finding important significance for catalyst design and CO2 utilization.

Regioselective Addition of Sulfur and Amine Nucleophiles To Assemble S═C-S, S-N, and Umpolung C-N Bonds: Exploration of the -CBr3 Group as a Synthetic Equivalent of S═C-S

The regioselective addition of sulfur and amine nucleophiles to a -CBr3 unit and nitromethyl moiety in a molecule with the installation of a five-diverse bond structure to novel isothiazole-5(2H)-thione is demonstrated. Umpolung of the nitromethyl group leads to a novel scaffold with selective C-N bond formation. Consequently, differentiating reactive centers by sulfur and amine nucleophiles has been proposed to create unique S-N bonds in conjunction with the dithioate (S═C-S-) moiety. This protocol allows for exploration of the -CBr3 moiety as a synthetic equivalent of the dithioate (S═C-S-) unit during the reaction.

Synthesis of Oxazolidines and Dihydroxazines via Cyclization of α-Aminated Ketones

A new approach to oxazolidines and dihydroxazines was developed by regioselective cyclization of α-aminated ketones under transition metal-free conditions. Oxazolidine derivatives were generated in the presence of chloro benziodoxole and TFA, while dihydroxazines were formed without a hypervalent iodine reagent. The reaction was performed under room temperature and gave the products in good to excellent yields.

Adding Diversity to Diiron Aminocarbyne Complexes with Amine Ligands

The reactions of the diiron aminocarbyne complexes [Fe2Cp2(NCMe)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, 1aNCMe; R = Cy, 1bNCMe), freshly prepared from the tricarbonyl precursors 1a–b, with primary amines containing an additional function (i.e., alcohol or ether) proceeded with the replacement of the labile acetonitrile ligand and formation of [Fe2Cp2(NH2CH2CH2OR’)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, R’ = H, 2a; R = Cy, R’ = H, 2b; R = Cy, R’ = Me, 2c) in 81–95% yields. The diiron-oxazolidinone conjugate [Fe2Cp2(NH2OX)(CO)(μ-CO){μ-CN(Me)2}]CF3SO3, 3, was prepared from 1a, 3-(2-aminoethyl)-5-phenyloxazolidin-2-one (NH2OX) and Me3NO, and finally isolated in 96% yield. In contrast, the one pot reactions of 1a-b with NHEt2 in the presence of Me3NO gave the unstable [Fe2Cp2(NHEt2)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, 4a; R = Cy, 4b) as unclean products. All diiron complexes were characterized by analytical and spectroscopic techniques; moreover, the behavior of 2a–c and 3 in aqueous media was ascertained.

Highly Efficient Conversion of Aziridines and CO2 Catalyzed by Microporous [Cu12] Nanocages

The conversion of CO₂ as a C1 source into value-added products is an attractive alternative in view of the green synthesis. Among the reported approaches, the cyclization reaction of aziridines with CO₂ is of great significance since the generated N-containing cyclic skeletons are extensively found in pharmaceutical chemistry and industrial production. However, a low turnover number (TON) and homogeneous catalysts are often involved in this catalytic system. Herein, one novel copper-organic framework {[Cu₂(L^4-)(H₂O)₂]·3DMF·2H₂O}_n (1) (H₄L = 2'-fluoro-[1,1':4',1″-Terphenyl]-3,3″,5,5″-tetracarboxylic acid) assembled by nanosized [Cu₁₂] cages was successfully synthesized and structurally characterized, which exhibits high CO₂/N₂ selectivity due to the strong interactions between CO₂ and open Cu(II) sites and ligands in the framework. Catalytic investigations suggest that 1 as a heterogeneous catalyst can effectively catalyze the cyclization of aziridines with CO₂, and the TON can reach a record value of 90.5. Importantly, 1 displays excellent chemical stability, which can be recycled at least five times. The combination explorations of nuclear magnetic resonance (NMR), ¹³C-isotope labeling experiments, and density functional theory (DFT) clearly uncover the mechanism of this aziridine/CO₂ coupling reaction system, in which 1 and tetrabutylammonium bromide (TBAB) can highly activate the substrate molecule, and the synergistic catalytic effect between them can greatly reduce the reaction energy barrier from 51.7 to 36.2 kcal/mol.

Novel MCM-41 Supported Dicationic Imidazolium Ionic Liquids Catalyzed Greener and Efficient Regioselective Synthesis of 2-Oxazolidinones from Aziridines and Carbon Dioxide

A type of MCM-41 supported dicationic imidazolium ionic liquid nanocatalyst has been synthesized and found to be competent for the synthesis of 2-oxazolidinones through the sustainable chemical conversion of CO2 with aziridines. It was shown that the highest efficiency was achieved in the cycloaddition of a series of aziridines and CO2 in the presence of a catalytic amount of the solid catalyst MCM-41@ILLaCl4 under mild conditions. Merits of this meticulously designed protocol are the use of a novel supported ionic liquid catalyst, the easy work-up process, good to excellent yields, a short reaction time, and purification without column chromatography. Overall, the present protocol of synthesizing 2-oxazolidinones under cocatalyst- and solvent-free conditions using MCM-41@ILLaCl4 is promising for industrial applications.

Aziridination Reactivity of a Manganese(II) Complex with a Bulky Chelating Bis(Alkoxide) Ligand

Treatment of Mn(N(SiMe₃)₂)₂(THF)₂ with bulky chelating bis(alkoxide) ligand [1,1′:4′,1′′-terphenyl]-2,2′′-diylbis(diphenylmethanol) (H₂[O-terphenyl-O]^Ph) formed a seesaw manganese(II) complex Mn[O-terphenyl-O]^Ph(THF)₂, characterized by structural, spectroscopic, magnetic, and analytical methods. The reactivity of Mn[O-terphenyl-O]^Ph(THF)₂ with various nitrene precursors was investigated. No reaction was observed between Mn[O-terphenyl-O]^Ph(THF)₂ and aryl azides. In contrast, the treatment of Mn[O-terphenyl-O]^Ph(THF)₂ with iminoiodinane PhINTs (Ts = p-toluenesulfonyl) was consistent with the formation of a metal-nitrene complex. In the presence of styrene, the reaction led to the formation of aziridine. Combining varying ratios of styrene and PhINTs in different solvents with 10 mol% of Mn[O-terphenyl-O]^Ph(THF)₂ at room temperature produced 2-phenylaziridine in up to a 79% yield. Exploration of the reactivity of Mn[O-terphenyl-O]^Ph(THF)₂ with various olefins revealed (1) moderate aziridination yields for p-substituted styrenes, irrespective of the electronic nature of the substituent; (2) moderate yield for 1,1′-disubstituted α-methylstyrene; (3) no aziridination for aliphatic α-olefins; (4) complex product mixtures for the β-substituted styrenes. DFT calculations suggest that iminoiodinane is oxidatively added upon binding to Mn, and the resulting formal imido intermediate has a high-spin Mn(III) center antiferromagnetically coupled to an imidyl radical. This imidyl radical reacts with styrene to form a sextet intermediate that readily reductively eliminates the formation of a sextet Mn(II) aziridine complex.

Activation of CS2 with the 2H-Phosphindole Complex to Construct P,S-Polycycles

The activation of CS₂ by the 2H-phosphindole complex with a low-coordinate phosphadiene moiety is reported. The successive hetero-Diels-Alder reaction between 2H-phosphindoles and CS₂ constructs two bridged rings and one spirocycle simultaneously, affording structurally complex P,S-polycyclic products. The two 2H-phosphindoles approach the C═S bond in a head-to-head disposition to minimize steric hindrance. This work reveals the unique reactivity of low-coordinate organophosphorus species and their potential applications in small molecule activation.

Metal-assisted synthesis of salen-based porous organic polymer for highly efficient fixation of CO2 into cyclic carbonates

A series of metal–salen-based porous organic polymers was synthesized using a simple metal-assisted synthetic method, among which Co-salen-POP exhibited highly efficient performance in the fixation of CO2 into cyclic carbonates.

Amine-catalyzed site- and stereo-selective coupling of epoxy amines and carbon dioxide to construct oxazolidinones

NEt3 catalyzed the cycloaddition of epoxy amine and CO2, which generated oxazolidinones. Reactions of chiral epoxy amine achieved 100% configuration inversion, enabling the synthesis of linezolid. DFT studies show that NEt3 acted as a nucleophile.

An uncommon multicentered ZnI-ZnI bond-based MOF for CO2 fixation with aziridines/epoxides

A novel cluster-based MOF with uncommon multicentered Zn^I-Zn^I bonds {[K_1.2Na_2.8Zn^I₈(HL)₁₂]·4H₂O}_n (HL = tetrazole monoanion) (1) was synthesized, which showed higher stability than the reported Zn^I-Zn^I bonded compounds. Moreover, 1 can effectively and circularly catalyze the cyclization of CO₂ and aziridines or epoxides with five substituent groups. Importantly, this is the first time that the catalytic properties of MOFs with multicentered metal-metal bonded clusters as the catalyst have been studied.

Tandem Alkylation/Michael Addition Reaction of Dithiocarbamic Acids with Alkyl γ-Bromocrotonates: Access to Functionalized 1,3-Thiazolidine-2-thiones

Thiazolidine-2-thiones were prepared via a novel multicomponent reaction of primary amines (amino acids), carbon disulfide, and γ-bromocrotonates. The reaction proceeds via a domino alkylation/intramolecular Michael addition to provide the corresponding thiazolidine-2-thiones in high to excellent yields. By using diamines in this protocol, bis(thiazolidine-2-thiones) derivatives were synthesized. The synthetic utility of the adducts was demonstrated by hydrolysis, amidation, and oxidation reactions.

A comprehensive survey upon diverse and prolific applications of chitosan-based catalytic systems in one-pot multi-component synthesis of heterocyclic rings

Heterocyclic compounds are among the most prestigious and valuable chemical molecules with diverse and magnificent applications in various sciences. Due to the remarkable and numerous properties of the heterocyclic frameworks, the development of efficient and convenient synthetic methods for the preparation of such outstanding compounds is of great importance. Undoubtedly, catalysis has a conspicuous role in modern chemical synthesis and green chemistry. Therefore, when designing a chemical reaction, choosing and or preparing powerful and environmentally benign simple catalysts or complicated catalytic systems for an acceleration of the chemical reaction is a pivotal part of work for synthetic chemists. Chitosan, as a biocompatible and biodegradable pseudo-natural polysaccharide is one of the excellent choices for the preparation of suitable catalytic systems due to its unique properties. In this review paper, every effort has been made to cover all research articles in the field of one-pot synthesis of heterocyclic frameworks in the presence of chitosan-based catalytic systems, which were published roughly by the first quarter of 2020. It is hoped that this review paper can be a little help to synthetic scientists, methodologists, and catalyst designers, both on the laboratory and industrial scales.

Diethylammonium iodide as catalyst for the metal-free synthesis of 5-aryl-2-oxazolidinones from aziridines and carbon dioxide

The catalytic potential of ammonium halide salts was explored in the coupling reaction of a model aziridine with carbon dioxide, highlighting the superior activity of [NH2Et2]I. Then, working at room temperature, atmospheric CO2 pressure and in the absence of solvent, the [NH2Et2]I-catalyzed synthesis of a series of 5-aryl-2-oxazolidinones was accomplished in good to high yields and excellent selectivity, from 2-aryl-aziridines with N-methyl or N-ethyl groups. NMR studies and DFT calculations outlined the pivotal role of both the diethylammonium cation and the iodide anion. The proposed method represents a convenient choice for obtaining a limited number of valuable molecules for which more complex and more expensive catalytic systems have been reported even in recent years.

Non-precious metal carbamates as catalysts for the aziridine/CO2 coupling reaction under mild conditions

The catalytic potential of a large series of easily available metal carbamates (based on thirteen different non-precious metal elements) was explored for the first time in the coupling reaction between 2-aryl-aziridines and carbon dioxide, working under solventless and ambient conditions and using tetraalkylammonium halides as co-catalysts. The straightforward synthesis of novel [NbCl3(O2CNEt2)2], NbCl, and [NbBr3(O2CNEt2)2], NbBr, is reported. The niobium complex NbCl, in combination with NBu4I, emerged as the best catalyst of the overall series to convert aziridines with small N-alkyl substituents into the corresponding 5-aryl-oxazolidin-2-ones.

Asymmetric epoxidation of α,β-unsaturated ketones catalyzed by rare-earth metal amides RE[N(SiMe3)2]3 with chiral TADDOL ligands

The first application of rare-earth metal catalyst combined with TADDOLs in the asymmetric epoxidation of α,β-unsaturated ketones is disclosed.

Aziridine used as a vinylidene unit in palladium-catalyzed [2 + 2 + 1] domino annulation

A series of chromone fused methylenecyclopentanes are efficiently constructed in moderate to good yields by Pd-catalyzed [2 + 2 + 1] annulation, in which aziridine is used as a vinylidene unit by cleavage of two C–N bonds for the first time.

Carbon dioxide based methodologies for the synthesis of fine chemicals

Rapid environmental changes triggered by the increase in the concentration of heat-absorbing gases such as CO2 in the atmosphere have become a major cause of concern. One of the ways to counter this growing threat will be to efficiently convert atmospheric CO2 into value-added products via the development of efficient transition-metal-catalyzed processes. Conversion of CO2 into bulk products such as CH3OH and methane as well as its incorporation into commercial polyurethane synthesis has been achieved and reviewed extensively. However, the efficient transformation of CO2 into fine chemicals and value-added chemicals has many fold advantages. Recent years have seen a rapid rise in the number of metal-mediated protocols to achieve this goal of converting CO2 into fine chemicals. These are essential developments given the requirement of several commodities and fine chemicals in various industrial processes and the utilization of atmospheric CO2 will help provide a sustainable solution to the current environmental problems. Accordingly, we present here a comprehensive compilation of catalytic processes, involving CO2 as the C1 source for reacting with substrates such as alkanes, alkenes, alkynes, amines, acid chlorides, alcohols, allyl boronates, alkenyl triflates, and many others to provide easy access to a wide variety of useful molecules. Such a technology would certainly prove to be beneficial in solving the problems associated with the environmental accumulation of CO2.

Bypassing the Inertness of Aziridine/CO2 Systems to Access 5-Aryl-2-Oxazolidinones: Catalyst-Free Synthesis Under Ambient Conditions

The development of sustainable synthetic routes to access valuable oxazolidinones via CO₂ fixation is an active research area, and the aziridine/carbon dioxide coupling has aroused a considerable interest. This reaction features a high activation barrier and thus requires a catalytic system, and may present some other critical issues. Here, the straightforward gram-scale synthesis of a series of 5-aryl-2-oxazolidinones was developed at ambient temperature and atmospheric CO₂ pressure, in the absence of any catalyst/co-catalyst. The key to this innovative procedure consists in the direct transfer of the pre-formed amine/CO₂ adduct (carbamate) to common aziridine precursors (dimethylsulfonium salts), replacing the classical sequential addition of amine (intermediate isolation of aziridine) and then CO₂ . The reaction mechanism was investigated by NMR spectroscopy and DFT calculations applied to model cases.

Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth Metal Complexes Containing Trost Ligands

Four chiral dinuclear rare-earth metal complexes [REL¹]₂ (RE = Y(1), Eu(2), Nd(3), La (4)) stabilized by Trost proligand H₃L¹ (H₃L¹ = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol) were first prepared, and all were characterized by X-ray diffraction. Complex 4 was employed as the catalyst for enantioselective hydroboration reaction of substituted ketones, and the corresponding secondary alcohols with excellent yields and high ee values were obtained using reductant HBpin. The same result was also achieved using the combination of lanthanium amides La[N(SiMe₃)₂]₃ with Trost proligand H₃L¹ in a 1:1 molar ratio. The experimental findings and DFT calculation revealed the possible mechanism of the enantioselective hydroboration reaction and defined the origin of the enantioselectivity in the current system.

Bifunctional phase-transfer catalysts for synthesis of 2-oxazolidinones from isocyanates and epoxides

A series of bifunctional phase-transfer catalysts (PTCs) were synthesized to catalyze the [3 + 2] coupling reaction of isocyanates and epoxides to afford 2-oxazolidinones in good to high yields (up to 92% yield) using PhCl as a solvent at 100 °C within 12 h. These bifunctional PTCs were easily prepared from commercially available tertiary-primary diamines and isocyanates (or isothiocyanates, mono-squaramides, respectively) in two simple steps with good modularity and demonstrated high efficiency (2.5 mol% catalyst-loading). The synergistic interaction of the quaternary ammonium salt center and hydrogen-bond donor group in the catalyst with the substrate is crucial to this atom-economic reaction.

A designed and potentially decadentate ligand for use in lanthanide(iii) catalysed biomass transformations: targeting diastereoselective trans-4,5-diaminocyclopentenone derivatives

The catalysis of furfural to diastereoselective trans-4,5-diaminocyclopentenone building blocks for natural product synthesis for a wide range of amines was achieved under mild aerobic conditions.

Photoswitchable Cu(ii)/Cu(i) catalyses assisted by enzyme-like non-covalent interactions in Cu(ii)–melamine coordination polymers for installing CO2/CS2 and CF3 groups in heterocycles

This study describes photoswitchable Cu(ii)/Cu(i) catalyses and enzyme-like interactions in Cu–TDPAT for installing CO₂/CS₂ and CF₃ groups in heterocycles.

Lanthanide clusters as highly efficient catalysts regarding carbon dioxide activation

Lanthanide clusters display a wide substrate scope and high catalytic activity for the insertion of CO₂ into epoxides to form cyclic carbonates.

Synthesis of Oxazolidinones by using Carbon Dioxide as a C1 Building Block and an Aluminium-Based Catalyst

Oxazolidinone synthesis through the coupling of carbon dioxide and aziridines was catalysed by an aluminium(salphen) complex at 50-100 °C and 1-10 bar pressure under solvent-free conditions. The process was applicable to a variety of substituted aziridines, giving products with high regioselectivity. It involved the use of a sustainable and reusable aluminium-based catalyst, used carbon dioxide as a C₁ source and provided access to pharmaceutically important oxazolidinones as illustrated by a total synthesis of toloxatone. This protocol was scalable, and the catalyst could be recovered and reused. A catalytic cycle was proposed based on stereochemical, kinetic and Hammett studies.

Recent Advances in the Chemical Fixation of Carbon Dioxide: A Green Route to Carbonylated Heterocycle Synthesis

Carbon dioxide produced by human activities is one of the main contributions responsible for the greenhouse effect, which is modifying the Earth’s climate. Therefore, post-combustion CO2 capture and its conversion into high value-added chemicals are integral parts of today’s green industry. On the other hand, carbon dioxide is a ubiquitous, cheap, abundant, non-toxic, non-flammable and renewable C1 source. Among CO2 usages, this review aims to summarize and discuss the advances in the reaction of CO2, in the synthesis of cyclic carbonates, carbamates, and ureas appeared in the literature since 2017.

Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers

Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.