Catalytic Method Research Articles

Rh-catalyzed asymmetric cyclopropanation of benzofurans with trifluoromethyl N-triftosylhydrazones

An asymmetric dearomative cyclopropanation of benzofuran has been accomplished by a novel catalytic method that relies on using trifluoromethyl N-triftosylhydrazones as carbene sources in the presence of a chiral rhodium catalyst. This reaction produces chiral trifluoromethyl-tethered 2,3-disubstituted benzofuran cyclopropane, which carries versatile pharmacophores 2,3-dihydrobenzofuran and trifluoromethyl-substituted quaternary carbon centers. Notably, this process offers distinct advantages over other existing approaches due to being step-economic and eliminating green-gas N2 as a harmless coproduct. DFT calculations explain the reason behind the high enantioselectivity during this cyclopropanation reaction.

Chromatography-free synthesis of carbamates from CO2 catalyzed by a green and recyclable biobased ionic liquid/Cu2O system

Carbamates and related derivatives are crucial skeletons for pesticide design and pharmaceutical chemistry. Recently, a synthetic route for the production of carbamates has drawn great attention, which assembles the economical, renewable and non-toxic CO2 with propargyl alcohols and amines. This route is 100% atom-economical and free of traditional carbon sources (CO, phosgene, etc.), thus attracting scientists to develop numerous catalytic methods for its effective applications. However, the carbamates produced in these methods generally contained residual catalysts, solvents or byproducts. Consequently, column chromatography purification is inevitably required for all the reports up to now. This limitation has fundamentally hindered the practical application of this route. Herein, a chromatography-free method was proposed for the first time. With the catalysis of a green and economical Cu2O/biobased ionic liquid system, the carbamates could be obtained in good to excellent yields and purity. Additionally, the catalytic metal loading reached the lowest level reported by far under 1 bar of CO2. Furthermore, this catalytic system could be recycled and reused for at least 5 times.

Electrosynthetic Carboxylation of Biomass-Derived Compounds in Ionic Liquids

Chemical production from renewable biomass and CO2 is a sustainable alternative to the current fossil based chemical industry as it will enable significant reduction of greenhouse gas emissions. CO2 is a desirable chemical building block as it is abundant and steadily becoming more available as carbon capture technologies are maturing. However, activation and valorization of CO2 remains a challenge due to its thermodynamic stability and kinetic inertness. CO2 activation has been demonstrated with thermal, (photo)catalytic and electrochemical methods, and especially the electrochemical approach allows for mild reaction conditions and high efficiency. In this context, the synthesis of carboxylic acids by electrosynthetic carboxylation represents an interesting strategy for valorization of biomass-derived alcohols and CO2.In electrosynthesis, a supporting electrolyte salt is needed in the reaction medium to ensure high conductivity. A major drawback of using such a supporting electrolyte salt is increased waste generation. However, by replacing supporting electrolyte salts with recyclable ionic liquids the waste generation can in theory be avoided. In addition, ionic liquids can provide a highly conducting reaction medium with a sufficiently large electrochemical window allowing CO2 activation to take place. Furthermore, room temperature ionic liquids are especially suitable for electrosynthetic carboxylation reactions due to their high CO2 absorption capacity.In this work, we present preliminary results, including cyclic voltammetry and reaction optimization studies, for electrosynthetic C-O activation and carboxylation of biomass-derived compounds with room temperature ionic liquids as electrolytes.

Single‐Atom Manganese‐Catalyzed Oxygen Evolution Drives the Electrochemical Oxidation of Silane to Silanol

AbstractThe oxygen evolution reaction (OER), characterized by a four‐electron transfer kinetic process, represents a significant bottleneck in improving the efficiency of hydrogen production from water electrolysis. Consequently, extensive research efforts have been directed towards identifying single‐atom electrocatalysts with exceptional OER performance. Despite the comprehensive understanding of the OER mechanism, its application to other valuable synthetic reactions has been limited. Herein, we leverage the MOOH intermediate, a key species in the Mn−N−C single‐atom catalyst (Mn‐SA@NC), which can be cyclically delivered in the OER. We exploit this intermediate’ s capability to facilitate electrophilic transfer with silane, enabling efficient silane oxidation under electrochemical conditions. The SAC electrocatalytic system exhibits remarkable performance with catalyst loadings as low as 600 ppm and an exceptional turnover number of 9132. Furthermore, the catalytic method demonstrates stability under a 10 mmol flow chemistry setup. By serving as an OER electrocatalyst, the Mn‐SA@NC drives the entire reaction, establishing a practical Mn SAC‐catalyzed organic electrosynthesis system. This synthesis approach not only presents a promising avenue for the utilization of electrocatalytic OER but also highlights the potential of SACs as an attractive platform for organic electrosynthesis investigations.

Single-Atom Manganese-Catalyzed Oxygen Evolution Drives the Electrochemical Oxidation of Silane to Silanol.

The oxygen evolution reaction (OER), characterized by a four-electron transfer kinetic process, represents a significant bottleneck in improving the efficiency of hydrogen production from water electrolysis. Consequently, extensive research efforts have been directed towards identifying single-atom electrocatalysts with exceptional OER performance. Despite the comprehensive understanding of the OER mechanism, its application to other valuable synthetic reactions has been limited. Herein, we leverage the MOOH intermediate, a key species in the Mn-N-C single-atom catalyst (Mn-SA@NC), which can be cyclically delivered in the OER. We exploit this intermediate' s capability to facilitate electrophilic transfer with silane, enabling efficient silane oxidation under electrochemical conditions. The SAC electrocatalytic system exhibits remarkable performance with catalyst loadings as low as 600 ppm and an exceptional turnover number of 9132. Furthermore, the catalytic method demonstrates stability under a 10 mmol flow chemistry setup. By serving as an OER electrocatalyst, the Mn-SA@NC drives the entire reaction, establishing a practical Mn SAC-catalyzed organic electrosynthesis system. This synthesis approach not only presents a promising avenue for the utilization of electrocatalytic OER but also highlights the potential of SACs as an attractive platform for organic electrosynthesis investigations.

Catalytic Enantioselective Synthesis of Axially Chiral Imidazoles by Cation-Directed Desymmetrization.

Axially chiral five-membered heterobiaryls synthesized by enantioselective catalysis typically feature large ortho-substituents or a heteroatom in the chiral axis to maintain a stable configuration. Herein we report a cation-directed catalytic enantioselective desymmetrization method that enables rapid access to axially chiral imidazoles with the basic nitrogen at the ortho position and efficiently integrates π-stacking moieties to ensure a stable axial configuration for further applications. The process is operationally simple, is highly enantioselective, and can be performed on the gram scale. The majority of the products are obtained in >90% ee, but interestingly even those with only moderate ee can readily be enriched to near optical purity by selective racemate crystallization. Together with a mild phosphine oxide reduction method, axially chiral imidazoles such as StackPhos and its derivatives are readily prepared in high yield and excellent enantioselectivity on the gram scale. The method also enables the preparation of new chiral non-phosphine-bearing imidazoles.

Silver Nitrate Catalyzed Sulfonylation of O-Propargyl Alkynes

AbstractThe development of new catalytic methods based on lower-cost metals under environmentally friendly conditions is still a challenge. Herein, we report an efficient strategy for the synthesis of vinyl sulfones from O-propargyl alkynes and sodium salts of sulfinic acids using silver nitrate, an inexpensive and readily available catalyst, under air atmosphere using aqueous conditions. The products were obtained in good to moderate yields, and the mechanism of the reaction was also investigated.

Direct Synthesis of Phosphoryltriacetates from White Phosphorus via Visible Light Catalysis.

Organophosphorus compounds (OPCs) are widely used in many fields. However, traditional synthetic routes in the industry usually involve multistep and hazardous procedures. Therefore, it's of great significance to construct such compounds in an environmentally-friendly and facile way. Herein, a photoredox catalytic method has been developed to construct novel phosphoryltriacetates. Using fac-Ir(ppy)3 (ppy=2-phenylpyridine) as the photocatalyst and blue LEDs (456 nm) as the light source, white phosphorus can react with α-bromo esters smoothly to generate phosphoryltriacetates in moderate to good yields. This one-step approach features mild reaction conditions and simple operational process without chlorination.

Lindgrenite as an efficient heterogeneous catalyst to obtain biodiesel

Lindgrenite, Cu3MoO42OH2, presents considerable potential to be used as a catalyst for obtaining biodiesel from soybean oil and methanol. Lindgrenite samples were obtained using conventional coprecipitation and ultrasound-assisted coprecipitation methods. Several catalytic tests were performed to reach the optimal conditions (methanol/oil molar ratio: 45/1, catalyst mass: 1%, reaction time: 4 h, reaction temperature: 180 °C) for obtaining biodiesel, with a 96% yield in the first catalytic cycle and 85% yield in its tenth catalytic cycle. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) of the biodiesel obtained by catalytic method revealed negligible amount of leached metal ions (less than 1 ppm of Cu2+ and less than 3 ppm of Mo6+) with the catalyst obtained by ultrasound-assisted coprecipitation method. The similarity between the FTIR spectra of industrial biodiesel and that obtained in this work confirms the effectiveness of using lindgrenite as an efficient catalyst for the transesterification reaction. Biodiesel synthesis was also confirmed by Nuclear Magnetic Resonance (1H and 13C NMR). The results obtained from Gas Chromatography-Mass Spectrometry (GC-MS) indicate methyl linoleate is the main component of the biodiesel, corresponding to approximately 50.50%. In addition to being easily obtained, lindgrenite is thermally stable and efficient under the applied conditions. The 96% yield after the fifth catalytic cycle is above the catalytic performance commonly observed in the literature. These characteristics indicate that lindgrenite has enormous potential to be used as a new heterogeneous catalyst to obtain biodiesel.

Copper on charcoal: TEMPO free Cu0 nanoparticles catalyzed aerobic oxidation of alcohols

A highly efficient and Tempo-free catalytic aerobic alcohol oxidation method has been developed using charcoal-supported Cu0 nanoparticles（Cu-A） in conjunction with pyridine. Various alcohols, bearing different functional groups, can be readily oxidized to their corresponding ketones and aldehydes under mild conditions.

Dual-Catalysed Intermolecular Reductive Coupling of Dienes and Ketones.

We report a mild, catalytic method for the intermolecular reductive coupling of feedstock dienes and styrenes with ketones. Our conditions allow concomitant formation of a cobalt hydride species and single-electron reduction of ketones. Subsequent selective hydrogen-atom transfer from the cobalt hydride generates an allylic radical which can selectively couple with the persistent radical-anion of the ketone. This radical-radical coupling negates unfavourable steric interactions of ionic pathways and avoids the unstable alkoxy radical of previous radical olefin-carbonyl couplings, which were limited, as a result, to aldehydes. Applications of this novel and straightforward approach include the efficient synthesis of drug molecules, key intermediates in drug synthesis and site-selective late-stage functionalisation.

Dual‐katalysierte intermolekulare reduktive Kopplung von Dienen und Ketonen**

AbstractWir berichten über eine milde, katalytische Methode für die intermolekulare reduktive Kopplung von Dienen und Styrolen mit Ketonen. Unsere Bedingungen ermöglichen die gleichzeitige Bildung einer Cobalthydrid‐Spezies und die Ein‐Elektronen‐Reduktion von Ketonen. Der anschließende selektive Wasserstoff‐Atom‐Transfer vom Cobalthydrid erzeugt ein allylisches Radikal, das sich selektiv mit dem persistenten Radikal‐Anion des Ketons verbinden kann. Diese Radikal‐Radikal‐Kopplung hebt die ungünstigen sterischen Wechselwirkungen der Ionenwege auf und vermeidet das instabile Alkoxy‐Radikal früherer radikalischer Olefin‐Carbonyl‐Kopplungen, die infolgedessen auf Aldehyde beschränkt waren. Zu den Anwendungen dieser neuen Methode gehören die effiziente Synthese von Arzneimittelmolekülen, wichtige Zwischenprodukte in der Arzneimittelsynthese und die ortselektive Late‐Stage‐Funktionalisierung.

ANALYSIS OF WASTE GAS CLEANING METHODS FROM SULFUR DIOXIDE

It is shown that sulfur dioxide is one of the most common components of harmful emissions into the atmosphere.
 It is presented that a large amount of SO2 is emitted into the atmosphere in the production of sulfuric acid, during the combustion of fuel in thermal power plants, in modern production of surfactants.
 Sulfur dioxide has been shown to be responsible for the formation of acid rain, which is one of the most common forms of pollution worldwide.
 The transport of sulfur compounds over long distances leads to the deposition of sulfur dioxide in soils and waterways.
 It is known that all known methods of waste gas purification are divided into three main groups: ammonia methods, SO2 neutralization methods, catalytic methods.
 In the general case, absorption methods are divided into open and circulating cleaning schemes.
 It is shown that ammonia-acid methods are economical, but require the cost of a scarce product – ammonia.
 The ammonia-sulfuric acid method consists in the treatment of ammonium bisulfite with sulfuric acid.
 When using the ammonia-phosphorus-acid method, phosphorus methods and sulfuric acid are formed.
 The soda method is based on the absorption of sulfur dioxide by a suspension of CaO.
 The lime method is based on the absorption of sulfur dioxide by a suspension of CaO.
 It is shown that when using a sodium hydroxide solution as an absorbent, both open-loop and circulating cleaning schemes are used.
 Open circuits are characterized by simple hardware design, as well as low energy for cleaning.
 It has been shown that catalytic methods for cleaning exhaust gases do not require the use of an absorbent. However, it is necessary to use an expensive catalyst. More often, this method is used at the first stage of cleaning, and at the second – the above methods of cleaning.
 A table with comparative technical and economic indicators is given.
 It is shown that for the production of surfactants it is better to use open-loop purification schemes.
 It is suggested that sodium hydroxide solution can be chosen as the absorbent. With the content of small amounts of sodium sulfite in a solution of sodium hydroxide, it can be used as a neutralizing agent in the neutralization of sulfation products.

ANALYSIS OF WASTE GASES CLEANING METHODS FROM SULFUR DIOXIDE

It is shown that sulfur dioxide is one of the most common components of harmful emissions into the atmosphere. It is stated that a large amount of SO2 is emitted into the atmosphere in the production of sulfuric acid, during fuel combustion in thermal power plants, and in modern production of surface-active substances.
 It has been shown that sulfur dioxide is responsible for the formation of acid rain, which is one of the most common forms of pollution around the world.
 It is stated that all known methods of waste gas purification are divided into three main groups: ammonia methods, SO2 neutralization methods, catalytic methods.
 In general, absorption methods are divided into open and circulation cleaning schemes.
 It is shown that ammonia-acid methods are economical, but require consumption of a scarce product - ammonia.
 The ammonia-sulfuric-acid method consists in treating ammonium bisulfite with sulfuric acid.
 When using the ammonia-phosphoric-acid cleaning method, phosphoric fertilizers and SO2 are formed, which can be further processed into sulfuric acid.
 The sodium method is based on the absorption of sulfur dioxide by a CaO suspension.
 It is indicated that when using a solution of sodium hydroxide as an absorbent, both open and circulating cleaning schemes are used.
 It is shown that catalytic methods of waste gas purification do not require the use of an absorbent. However, it is necessary to use an expensive catalyst. Most often, this method is used at the first stage of cleaning, and at the second - the cleaning methods listed above.
 The table with comparative technical and economic indicators is presented, the choice of one or another cleaning method depends on specific production conditions.
 It is shown that for the production of surface-active substances it is better to use open cleaning schemes, which are distinguished by the simplicity of the equipment design, as well as the low consumption of energy for cleaning.
 It is stated that sodium hydroxide solution can be chosen as an absorbent. If the sodium hydroxide solution contains small amounts of sodium sulfite, it can be used as a neutralizing agent in the neutralization of sulfation products.

Asymmetric Photoaerobic Lactonization and Aza-Wacker Cyclization of Alkenes Enabled by Ternary Selenium-Sulfur Multicatalysis.

An adaptable, sulfur-accelerated photoaerobic selenium-π-acid ternary catalyst system for the enantioselective allylic redox functionalization of simple, nondirecting alkenes is reported. In contrast to related photoredox catalytic methods, which largely depend on olefinic substrates with heteroatomic directing groups to unfold high degrees of stereoinduction, the current protocol relies on chiral, spirocyclic selenium-π-acids that covalently bind to the alkene moiety. The performance of this ternary catalytic method is demonstrated in the asymmetric, photoaerobic lactonization and cycloamination of enoic acids and unsaturated sulfonamides, respectively, leading to an averaged enantiomeric ratio (er) of 92:8. Notably, this protocol provides for the first time an asymmetric, catalytic entryway to pharmaceutically relevant 3-pyrroline motifs, which was used as a platform to access a 3,4-dihydroxyproline derivative in only seven steps with a 92:8 er.

Catalyst control over pentavalent stereocentres

A monumental diversity of catalytic methods imparts the ability to select one of two configurations of tetravalent stereocentres. Conversely, catalyst control over pentavalent stereocentres, where a fifth moiety bound to the central atom encodes an expanded stereochemical space, remained a challenge to be accomplished. Herein, we report the feasibility of the catalytic tractability of pentavalent stereocentres. A bifunctional iminophosphorane thiourea catalyst enables enantio- and diastereocontrol over pentavalent phosphoranes to differentiate configurationally stable enantiomers and ensembles of diastereomers which emerge together from a single stereocentre. The desired dioxophosphorane stereoisomers are obtained with excellent yield and selectivity (up to 99% yield, 96:4 e.r. and 99:1 d.r.), while stereodivergent catalysis reroutes the reaction for selective access to each of the viable stereoisomeric states of pentavalent phosphoranes. Considering the diversity of high-valent main group species, it is expected that catalyst control over pentavalent stereocentres significantly increases the synthetically addressable stereochemical space.

Ruthenium-Catalyzed Self-Coupling of Secondary Alcohols.

A simple catalytic method for self-coupling of secondary alcohols leading to the synthesis of β-branched ketones under mild conditions is reported. Well-defined ruthenium pincer complex catalyzed the reactions. Optimization studies revealed that sodium tert-butoxide is an appropriate base for this transformation. Functionalized aryl methanols, heteroaryl methanols, and linear and branched aliphatic secondary alcohols underwent facile catalytic self-coupling reactions. Mechanistic studies revealed that both catalyst and base are crucial to achieve dehydrogenation of secondary alcohols to ketones, their subsequent controlled aldol condensation, and further hydrogenation of α,β-unsaturated intermediates, leading to the selective formation of β-branched ketone products. Notably, the noninnocent PNP ligand which displays amine-amide metal-ligand cooperation operative in a catalyst played a key role in facilitating this catalytic self-coupling of secondary alcohols. Liberated molecular hydrogen and water are the only byproducts.

Nickel/photoredox dual catalyzed arylalkylation of nonactivated alkenes

Alkene dicarbofunctionalization is an efficient strategy and operation-economic fashion for introducing complexity in molecules. A nickel/photoredox dual catalyzed arylalkylation of nonactivated alkenes for the simultaneous construction of one C(sp3)−C(sp3) bond and one C(sp3)−C(sp2) bond has been developed. The mild catalytic method provided valuable indanethylamine derivatives with wide substrate scope and good functional group compatibility. An enantioselective dicarbofunctionalization was also achieved with pyridine-oxazoline as a ligand. The efficiency of metallaphotoredox dicarbofunctionalization was demonstrated for the concise synthesis of pharmaceutically active compounds.

Autoxidation Catalysis for Carbon-Carbon Bond Cleavage in Lignin.

Selective lignin depolymerization is a key step in lignin valorization to value-added products, and there are multiple catalytic methods to cleave labile aryl-ether bonds in lignin. However, the overall aromatic monomer yield is inherently limited by refractory carbon-carbon linkages, which are abundant in lignin and remain intact during most selective lignin deconstruction processes. In this work, we demonstrate that a Co/Mn/Br-based catalytic autoxidation method promotes carbon-carbon bond cleavage in acetylated lignin oligomers produced from reductive catalytic fractionation. The oxidation products include acetyl vanillic acid and acetyl vanillin, which are ideal substrates for bioconversion. Using an engineered strain of Pseudomonas putida, we demonstrate the conversion of these aromatic monomers to cis,cis-muconic acid. Overall, this study demonstrates that autoxidation enables higher yields of bioavailable aromatic monomers, exceeding the limits set by ether-bond cleavage alone.

Peroxygenase-Catalysed Sulfoxidations in Non-Aqueous Media.

Chiral sulfoxides are valuable building blocks in asymmetric synthesis. However, the biocatalytic synthesis of chiral sulfoxides is still challenged by low product titres. Herein, we report the use of peroxygenase as a catalyst for asymmetric sulfoxidation under non-aqueous conditions. Upon covalent immobilisation, the peroxygenase showed stability and activity under neat reaction conditions. A large variety of sulfides was converted into chiral sulfoxides in very high product concentration with moderate to satisfactory optical purity (e. g. 626 mM of (R)-methyl phenyl sulfoxide in approx. 89 % ee in 48 h). Further polishing of the ee value via cascading methionine reductase A (MsrA) gave>99 % ee of the sulfoxide. The robustness of the enzymes and high product titer is superior to the state-of-the-art methodologies. Gram-scale synthesis has been demonstrated. Overall, we demonstrated a practical and facile catalytic method to synthesize chiral sulfoxides.