Mild Conditions Research Articles

Synthesis, Characterization, and Optimization of Novel Furan-ring Fused Chalcones via Radical Cyclization of α,β-Unsaturated Ketones and Cyclic Ketone

Abstract: Novel Furan-ring Fused Chalcones (FFC) were synthesized using a radical cyclization reaction of α,β-unsaturated ketones with cyclic ketone as the model reaction to attain this goal. In this study, traditional and microwave-assisted methods for the efficient and cost-effective synthesis of furan-ring fused chalcones in mild reaction conditions are compared and optimized. The goal is to develop a reliable and adaptable synthetic technique that may be used to produce these useful chalcone derivatives quickly and effectively. The optimal experimental conditions for these reactions were carefully determined using two independent methodologies: conventional (Method A) and microwave (Method B). The results indicated that the proposed method B could be used effectively in the future to synthesize novel furans with short reaction times and acceptable yields (87-94 %), and products were purified by column chromatography and preparative thin layer chromatography (PTLC). All new compounds were characterized by 1H-NMR, 13C-NMR, LC-MS, and elemental analyses.

Chemically recyclable rosin-based polymers

The pursuit of next-generation sustainable polymers with chemical recyclability and resource renewability has become a priority in materials science. Rosin, a widely available renewable natural biomass, holds promise in this regard. In this study, dehydroabietic acid was incorporated into a cyclooctene monomer structure as pendant groups. This tailored monomer with low ring strain possesses the ability to efficiently undergo ring-opening metathesis polymerization (ROMP), resulting in the synthesis of rosin-based unsaturated polymers with a fully hydrocarbon backbone. The molecular weight of these polymers, ranging from 50 kDa to 160 kDa, can be easily modulated by varying the monomer-to-catalyst feeding ratio. Remarkably, these amorphous polymers exhibit exceptional thermostability, with a decomposition temperature exceeding 400 °C. This type of polymer exhibits excellent acid and alkali resistance within a pH range of 3 to 11. Upon exposure to Grubbs II catalyst under mild conditions, these polymers undergo depolymerization back to the native monomer in a highly efficient manner, achieving a remarkable recovery ratio of approximately 95 %. It is evident that this innovative approach is not only relevant for the development of rosin-based polymers but also holds promise for informing the design of other renewable polymers with superior thermostability and enhanced chemical recyclability.

A Review on the Recent Progress of Layered Double Hydroxides (LDHs)-based Catalysts for Heterocyclic Synthesis

Abstract: Over the past decade, heterocyclic compounds and their derivatives have emerged as promising substances with potential pharmacological applications due to their interesting biological properties. The significance of heterocyclic compounds in drug discovery and development is evident from the fact that a majority of drugs in the pharmaceutical market incorporate heterocyclic compounds as active substances or ingredients. Various synthetic methods and advancements have been devised to prepare these heterocyclic compounds using diverse catalysts under mild conditions. Layered double hydroxides (LDHs)-based materials have gained considerable attention across different fields, and their usability can be significantly enhanced via the selection of metal cations, their molar ratios, surface complexation, and intercalation modifications. The synthesis and application of LDH-based materials as catalysts have garnered increasing interest due to their exceptional properties. Moreover, LDH-based materials have found extensive use as heterogeneous catalysts in the synthesis of numerous heterocyclic compounds. This review presents the latest developments in the catalytic application of LDH-based materials as solid heterogeneous catalysts in the synthesis of heterocyclic compounds, covering literature published from 2018 to 2023.

Plasma-catalytic CO2 methanation over Ni supported on MCM-41 catalysts: Effect of metal dispersion and process optimization

Catalytic carbon dioxide (CO2) conversion technologies can be important components in carbon capture, storage and utilization for CO2 mitigation and possible future economic activity and have gained significant attention globally in past decades. Electrified non-thermal plasma (NTP) catalysis enables CO2 hydrogenation into value-added chemicals under mild conditions. If the hybrid process is coupled with renewable energy and green hydrogen, it can be the promising solution to address the energy and carbon emission challenges. To enhance the energy efficiency of NTP-catalytic systems, bespoke catalyst design and process optimization are necessary. Here, using Ni catalysts supported on mesoporous MCM-41 and NTP-catalytic CO2 methanation as the model systems, the effects of Ni metal dispersion, argon (Ar) addition and residence time on the NTP catalysis were also studied. The findings show that (i) increased metal dispersion alone did not lead to significant enhancement in the performance of NTP catalysis (e.g., CH4 production rate: 31.4 × 10−5 mol/(s·gNi) for 42.6 % Ni dispersion vs. 26.8 × 10−5 mol/(s·gNi) for 25.1 % dispersion), (ii) Ar addition to the system led to the decreased methane production rate (e.g., CH4 selectivity decreased by ∼19 % due to the increase in Ar addition to the system from 5 to 50 mL/min), and (iii) optimization of the residence time could improve the performance of NTP-catalytic CO2 methanation (i.e., an extension of the residence time to 0.69 s resulted in the higher CO2 conversion of 72.7 % and CH4 selectivity of 95.9 % at 9.6 kV than that at 0.49 s and 11 kV).

TENSOR QUANTILE REGRESSION WITH LOW-RANK TENSOR TRAIN ESTIMATION.

Neuroimaging studies often involve predicting a scalar outcome from an array of images collectively called tensor. The use of magnetic resonance imaging (MRI) provides a unique opportunity to investigate the structures of the brain. To learn the association between MRI images and human intelligence, we formulate a scalar-on-image quantile regression framework. However, the high dimensionality of the tensor makes estimating the coefficients for all elements computationally challenging. To address this, we propose a low-rank coefficient array estimation algorithm based on tensor train (TT) decomposition which we demonstrate can effectively reduce the dimensionality of the coefficient tensor to a feasible level while ensuring adequacy to the data. Our method is more stable and efficient compared to the commonly used, Canonic Polyadic rank approximation-based method. We also propose a generalized Lasso penalty on the coefficient tensor to take advantage of the spatial structure of the tensor, further reduce the dimensionality of the coefficient tensor, and improve the interpretability of the model. The consistency and asymptotic normality of the TT estimator are established under some mild conditions on the covariates and random errors in quantile regression models. The rate of convergence is obtained with regularization under the total variation penalty. Extensive numerical studies, including both synthetic and real MRI imaging data, are conducted to examine the empirical performance of the proposed method and its competitors.

Recent Progress on Synthesis of Functionalized 1,5-Disubstituted Triazoles.

Immediately after the invention of 'Click Chemistry' in 2002, the regioselective 1,2,3- triazole scaffolds resulted from respective organic azides and terminal alkynes under Cu(I) catalysis have been well recognized as the functional heterocyclic core at the centre of modern organic chemistry, medicinal chemistry, and material sciences. This CuAAC reaction has several notable features including excellent regioselectivity, high-to-excellent yields, easy to execute, short reaction time, modular in nature, mild condition, readily available starting materials, etc. Moreover, the resulting regioselective triazoles can serve as amide bond isosteres, a privileged functional group in drug discovery and development. More than hundreds of reviews had been devoted to the 'Click Chemistry' in special reference to 1,4-disubstituted triazoles, while only little efforts were made for an opposite regioisomer i.e., 1,5-disubstituted triazole. Herein, we have presented various classical approaches for an expeditious synthesis of a wide range of biologically relevant 1,5- disubstituted 1,2,3-triazole analogues. The syntheses of such a class of diversly functionalized triazoles have emerged as a crucial investigation in the domain of chemistry and biology. This tutorial review covers the literature assessment on the development of various synthetic protocols for the functionalized 1,5-disubstituted triazoles reported during the last 12 years.

Synthesis of Methyl N-phenylcarbamate Derivatives by Xphos Pd G2 Catalyzed Intermolecular Amidation Reaction

Abstract: The utilization of palladium catalysts in cross-coupling reactions has emerged as a highly promising method for the facile formation of aryl C-N bonds, operating under mild conditions. In this study, we present an efficient approach for the synthesis of methyl N-phenyl carbamate derivatives through the intermolecular amidation of aryl chlorides, catalyzed by Xphos Pd G2. The developed protocol has demonstrated remarkable efficacy, offering several advantages. Notably, the intermolecular amidation reaction exhibited good chemoselectivity, allowing for the precise targeting of desired C-N bond formations while maintaining the integrity of other functional groups. Additionally, this methodology showcases exceptional functional group compatibility, accommodating a diverse array of moieties, including sensitive groups that are traditionally challenging to handle. The Xphos Pd G2 catalyst has proven to be instrumental in orchestrating this transformation, exhibiting high catalytic activity and selectivity. Furthermore, this protocol stands out for its operational simplicity, making it a practical choice for synthetic chemists seeking a straightforward and reliable route to access methyl N-phenyl carbamate derivatives. Overall, this study not only expands the synthetic toolbox for C-N bond formations, but also underscores the significance of palladium-catalyzed methodologies in modern organic synthesis. The reported findings hold substantial promise for applications in medicinal chemistry and material science, where the facile construction of aryl C-N bonds is of paramount importance.

Visible Light-promoted Preparation of 2,3-Dihydrobenzofurans and Coumaranones

Abstract: 2,3-Dihydrobenzofuran and coumaranone are readily available in numerous naturally occurring compounds. They mostly exist in plenty of food plants and medicinal plants. Such compounds constitute a series of flavor components and bioactive molecules. Their preparation has been an attractive field of research. In the past few decades, great efforts have been made in the preparation of the 2,3-dihydrobenzofuran structure through both metal-catalyzed and organocatalyzed ways. Visible light-promoted reactions sprang up in the early 21st century and represent a green manner of transformations. Under the irradiation of visible light, radicals could be generated under milder conditions. Thus, visible lightpromoted reactions spread widely in the field of chemical synthesis. In recent years, visible light-promoted preparation of 2,3-dihydrobenzofuran and coumaranone has been developed by different groups, including both intramolecular and intermolecular reactions. The benign reaction conditions allow better functional group-tolerance and lead to diverse structures. Several reviews on the synthesis of 2,3- dihydrobenzofuran have been reported. However, visible light-promoted approaches to such structures have not been well reviewed. Our review will cover the literature that has been reported on the discovery of 2,3- dihydrobenzofuran in food and visible light-promoted preparation of 2,3-dihydrobenzofuran, attempting to summarize the existing methods and provide guidance to the chemists on the present challenges.

An Exceptional Valorization of CuO Nanoparticles in Ionic Liquids as an Efficient Medium for the Electrophilic Substitution of Indole Towards the Formation of Bis(indolyl)methanes

Aim: Ionic liquids are promising green solvents with simple but unique structure-related physical properties such as negligible vapour pressure, exceptional thermal conductivity, remarkable thermal stability and their suitability and inertness towards a broad range of catalytic applications. CuO NPs have been addressed as a cost-effective and a reagent of a choice that necessitates only mild reaction conditions to offer a high yield of the desired products with exceptional selectivity in a short duration of time. Therefore, in the present work, attempts have been made to explore the catalytic potentials of CuO NPs in an ionic liquid medium to synthesize biologically important bis(indolyl)methanes. Background: Catalytic explorations of metal oxide nanoparticles in ionic liquids offers a cooperative effect that has a significant impact on the kinetics as well as on the outcome of the reaction. Therefore, such catalytic systems in the present times have seized the scientific community's interest from the perspectives of sustainable development in synthetic organic chemistry. The combination of metal oxide nanoparticles with highly tunable ionic liquids is not only used to synthesize simple organic molecules but also explored in the synthesis of complex organic molecules of high commercial and biological relevance. Objectives: The current work offers a rapid and robust protocol for synthesizing bis(indolyl)methanes via electrophilic substitution reaction between indole and various aldehydes in the presence of a CuO nanoparticles-ionic liquid system. The discussion focuses on the high tolerance of different functionalities by the catalytic system leading to the synthesis of bis(indolyl)methanes. Methods: CuO NPs have been synthesized via the co-precipitation method using ionic liquid. The applicability of metal oxide nanoparticles-IL matrix was further investigated in synthesizing bis(indolyl)methanes. Results: The FT-IR absorption below 600 cm-1 and the XRD pattern showing all the peaks in the diffraction diagram revealed the formation of CuO NPs. FESEM images show the flake-shaped morphology of CuO NPs and are found to be separated from the agglomerated clusters Conclusion: Ionic liquid-CuO NPs matrix reveals good to exceptional catalytic properties, and their advancements as a catalytic system at room temperature open new avenues for synthetic organic chemists.

Complete valorization of lignocellulose with one-step acidified monophasic phenoxyethanol fractionation.

Effective fractionation of lignocelluosic biomass and subsequent valorization of all three major components under mild conditions were achieved. Pretreatment with acidified monophasic phenoxyethanol (EPH) efficiently removed 92.6% lignin and 80% xylan from poplar at 110 ℃ in 60 min, yielding high-value EPH-xyloside, EPH-modified lignin (EPHL), and a solid residue nearly purely composed of carbohydrates. After removing the grafted acetyl groups using 1% NaOH at 50 ℃, the highest enzymatic digestibility reached 92.3%. EPHL could be recovered in high yield and purity with an uncondensed structure, while xylose was converted to EPH-xyloside, a potential precursor in biomedical industries. Additionally, the acidified monophasic EPH solvent could effectively fractionate biomass from species other than hardwood, achieving over 70% delignification from recalcitrant pinewood under the same mild conditions, demonstrating the high potential of monophasic EPH pretreatment.

Endomorphism Algebras of Support τ-Tilting Modules

Let [Formula: see text] be a finite dimensional [Formula: see text]-algebra and [Formula: see text] be a support [Formula: see text]-tilting right [Formula: see text]-module. In this note, we give lower and upper bounds for the global dimension of the endomorphism algebra [Formula: see text] under some mild conditions. Finally, we give some examples to illustrate that both the upper and lower bounds can be reached.

Hybrid Palladium-Catalyzed Intramolecular Carboamination of Conjugated Dienes: Synthesis of Functionalized Pyrrolidines via Selective Trifluoromethylarene Defluorination.

The incorporation of difluoromethylene groups into aza-heterocycles represents a compelling yet underexplored avenue in contemporary chemical research. In this study, we unveil a hybrid palladium-catalyzed intramolecular gem-difluoroalkylamination of conjugated dienes, providing a versatile approach to the synthesis of diverse functionalized pyrrolidines. Noteworthy features include mild reaction conditions and a remarkable tolerance toward various functional groups. Additionally, the use of alkyl iodides as electrophiles facilitates the generation of the corresponding alkylamination products. Control experiments support a proposed hybrid palladium-catalyzed radical-polar crossover pathway, offering insights into the underlying chemical processes governing this transformation.

Visible-Light-Induced Acylative Pyridylation of Styrenes.

A visible-light-induced photocatalyst-free acylative pyridylation of styrenes with 4-acyl-1,4-dihydropyridines (DHPs) and 4-cyanopyridines has been described, featuring mild reaction conditions, a broad substrate scope, and good functional group tolerance. The reaction could also be performed under sunlight irradiation albeit with a slightly lower conversion. 4-Acyl-1,4-DHPs serve a dual role, acting as both a photoreductant to reduce the cyanopyridine to its radical anion intermediate and a radical precursor to produce the acyl radical. The mechanism was especially elucidated through the Hammett analysis, with the quadratic linear regression analysis by using radical dual parameters, σmb and σjj·. The findings from Hammett analysis further demonstrate that the rate-limiting step of the process is the single electron transfer between 4-acyl-1,4-DHPs and 4-cyanopyridines.

Hypervalent Iodine Amino Acid Building Blocks for Bioorthogonal Peptide Macrocyclization.

Ethynylbenziodoxol(on)es (EB(X)xs) reagents have emerged as useful reagents for peptide/protein modification due to their versatile reactivity and high selectivity. Herein, we report the successful introduction of ethynylbenziodoxoles (EBxs) on different amino acid building blocks (Lys/Orn/Dap), and show their compatibility with both solid phase peptide synthesis (SPPS) and solution phase peptide synthesis (SPS). The selective incorporation of the EBx core into peptide sequences enable efficient macrocyclizations under mild conditions for the synthesis of topologically unique cyclic and bicyclic peptides.

Toward Designing Reactive Metal Clusters for Dinitrogen Activation: A Guideline Based on N2 Initial Adsorption.

Gas-phase metal clusters are ideal models to explore transition-metal-mediated N2 activation mechanism. However, the effective design and search of reactive clusters in N2 activation are currently hindered by the lack of clear guidelines. Inspired by the Sabatier principle, we discovered in this work that N2 initial adsorption energy (ΔEads) is an important parameter to control the N2 activation reactivity of metal clusters in the gas phase. This mechanistic insight obtained from high-level calculations rationalizes the N2 activation reactivity of many previously reported metal clusters when combined with the known factor determining the N≡N cleavage process. Furthermore, based on this guideline of ΔEads, we successfully designed several new reactive clusters for cleaving N≡N triple bond under mild conditions, including FeV2S2-, TaV2C2-, and TaV2C3-, the high N2 activation reactivity of which has been fully corroborated in our gas phase experiments employing mass spectrometry with collision-induced dissociation. The importance of ΔEads revealed in this work not only reshapes our understanding of N2 activation reactions in the gas phase but also could have implication for other N2 activation processes in the condensed phase. The more general establishment of this new perspective on N2 activation reactivity warrants future experimental and computational studies.

Electrochemical Synthesis of Phosphorylated Indoles and Trp-Containing Oligopeptides.

Cp2Fe-mediated electrochemical synthesis of phosphorylated indoles and Trp-containing oligopeptides has been developed, which eliminates the need for external oxidants and yields the desired products in moderate to excellent yields under mild conditions. Importantly, the synthetic applicability was further demonstrated through its easy scalability and the anticancer activity of the product. Remarkably, it presents the first electrochemical protocol to access the phosphorylation of indoles and Trp-containing oligopeptides.

Copper-Catalyzed Chemoselective Nitro Reduction

AbstractThe reduction of nitro compounds into the highly valuable anilines is reported using a Cu catalyst and B2Pin2. The reactions proceed under very mild conditions and showcase excellent functional group tolerance. This method is applied to a large panel of nitro derivatives, including biorelevant molecules and important synthetic intermediates, toward the synthesis of active pharmaceutical ingredients (APIs). This novel reaction manifold intends to provide a complementary approach to the existing portfolio of nitro-reduction methods.

Synthesis of sustainable chemicals and fuels from biomass derivatives using homogeneous ruthenium catalysts

This work describes the synthesis and evaluation as catalysts of two ruthenium(II) complexes, RuC1 and RuC2, containing NPN ligands=(N-(phenyl(pyridin-2-ylamino)phosphino)pyridin-2-amine and 2-((phenyl(pyridin-2-ylmethyl)phosphino)methyl)pyridine, respectively) for furfural and hydroxymethylfurfural hydrogenation. The catalysts displayed exceptional activity under mild conditions (180 °C, 40 bar H2) achieving over 98 % conversion and 98–99 % selectivity towards furfuryl alcohol (from furfural) and bis(hydroxymethyl)furan (from hydroxymethylfurfural) within 30 min, using a substrate-catalyst ratio of 3000:1. Remarkably, the catalysts maintained their efficacy even at a tenfold higher substrate loading (10,000:1), albeit with extended reaction times (3 and 4 h for furfural and hydroxymethylfurfural, respectively). Turnover frequencies (TOFs) were impressive, reaching 3920 h−1 and 3200 h−1 for furfural hydrogenation with the catalyst RuC1 and RuC2, respectively. Similarly, TOFs for hydroxymethylfurfural hydrogenation were 2450 h−1 and 2475 h−1 for RuC1 and RuC2, respectively. Notably, the catalysts exhibited excellent stability under reaction conditions. These findings demonstrate the promising potential of RuC1 and RuC2 for efficient hydrogenation of biomass-derived furans, offering a sustainable approach for the production of valuable bio-based chemicals.

Tetrahydropyran synthesis mediated by catalytic triflic acid and hexafluoroisopropanol

AbstractA Brønsted acid-catalyzed regioselective intramolecular hydroalkoxylation is described. This reaction proceeds via a carbocation intermediate and enables the preparation of 1,1,1’-trisubstituted tetrahydropyran derivatives under mild conditions using catalytic triflic acid (TfOH) and hexafluoroisopropanol (HFIP) as a mediator. Graphical abstract

Conformal Low‐Temperature Molecular Layer Deposited Coatings as Interface Modifications to Support Ceramic Protective Films on Macroscopic Flexible Devices

Flexible devices often need a protective coating when operating in harmful environments, ranging from mild ambient conditions to a biologically active environment of the human body. The flexibility poses a problem for traditional encapsulation solutions, as those make the device bulky and limit functionality by applying an external casing. Alternatively, fully conformal encapsulation of a device of arbitrary shape can be realized with thin‐film encapsulation (TFE) without altering device dimensions. Yet, TFE is susceptible to fail under mechanical stresses, especially when a hard ceramic coating is applied on a polymer. Reliability of TFE can be enhanced by altering the elasticity of the hard and brittle thin films, by adding softer layers in between sample and barrier. Herein, molecular layer deposited (MLD) metal‐linked trioxysilylheptanoate (M‐TOSH) films are studied for coating of large devices to conformally and uniformly tune the interface between polymer and atomic‐layer‐deposited protective film. The results show that M‐TOSH process scales to large chambers; parameter optimization leads to superior film quality and lowers elastic modulus. Conformality, tested with home‐built macroscopic test device, finds the process suitable for 3D parts. Final testing reveals that ten cycles of MLD interlayer double the crack‐onset‐strain from 0.26% to 0.51%.