Search Results (194)

The rational design of metal-free catalysts capable of efficiently converting CO₂ under atmospheric pressure remains a significant challenge in sustainable chemistry. Herein, we report a series of clamp-shaped dihydrogen-bonded iodide catalysts (CDBI catalysts) featuring a preorganized bifunctional framework that integrates dual hydrogen-bond donors and an intrinsic iodide nucleophile within a single molecular scaffold. Systematic structural variation revealed that catalytic activity is highly sensitive to electronic modulation, steric accessibility, and precise spatial arrangement between the hydrogen-bonding units and the iodide center. The optimal catalyst enabled solvent-free cycloaddition of CO₂ with epoxides at 1 atm CO₂, affording up to 99% conversion and >99% selectivity at 80 °C within 12 h. Substrate scope studies demonstrated efficient transformation of a wide range of terminal epoxides, while sterically demanding substrates exhibited reduced reactivity consistent with a confined activation mode. Mechanistic investigations support a cooperative pathway in which dual hydrogen-bond activation and proximal halide nucleophilicity operate synergistically within a preorganized clamp-shaped pocket. Comparative analysis with representative catalytic systems highlights the ability of this metal-free design to achieve high efficiency under atmospheric CO₂ without cocatalysts or solvents. These findings demonstrate that structural preorganization represents an effective strategy for promoting sustainable CO₂ utilization under operationally simple conditions. Full article

Recent advancements in heterogeneous catalysis have increased the interest in the synthesis of metal-free polymer-based catalysts. This work presents a novel approach for the solvent- and additive-free synthesis of a nitrogen-rich catalyst. Our unique procedure yields a non-porous organic polymer (NPOP) with a wide range of functional groups on the surface, attributed to the incomplete polymerization inherent to our solvent-free method. Detailed analysis revealed significant differences between NPOP and its Covalent Organic Framework counterpart. Remarkably, the absence of a high surface area did not hinder the efficiency of NPOP as a catalyst for the CO₂ cycloaddition. The performance of NPOP exceeded that of its COF counterpart, with a conversion rate of 99% for NPOP and 35% for the COF. An observation attributed to the abundance of nitrogen functional groups on the surface of NPOP. A combination of characterizations and density functional theory (DFT) calculations was employed to thoroughly understand the working mechanism of NPOP. The imines and secondary amines on the surface function as the active sites for the ring-opening of epichlorohydrin. This study supports existing theories that N atoms can serve as nucleophiles by donating their free electron pairs. Furthermore, the distinctive synthesis procedure reported here can serve as inspiration for further design of polymer-based catalysts. Full article

Ferrocenium-catalyzed transformations provide a practical and sustainable approach to propargylic substitution reactions. Herein, we investigate the ring-opening of cyclopropyl-substituted propargylic alcohols with alcohol nucleophiles, catalyzed by ferrocenium tetrafluoroborate ([FeCp₂][BF₄]) to afford synthetically valuable enyne ethers. Mechanistic studies using GC and NMR spectroscopy reveal that the reaction proceeds via initial formation of a ring-closed propargylic ether intermediate, which subsequently undergoes ring opening to the enyne ether. Experimental evidence supports a carbocationic pathway in which the ferrocenium cation promotes ionization to a stabilized cyclopropyl ether intermediate, followed by intramolecular, ferrocenium-assisted cyclopropyl ring opening to the enyne product. Reaction rates and product distributions are strongly influenced by temperature and solvent polarity, with polar solvents and elevated temperatures favoring ring opening. At room temperature, the ring-closed substitution product predominates, whereas efficient formation of enynes occurs at 65 °C. The reaction progresses faster in a polar solvent, indicating an ionic mechanism. Studies employing substrates containing substituted cyclopropyl rings demonstrated pronounced regioselectivity during nucleophilic ring opening with alcohols, with preferential cleavage of the bond between the two substituted carbon atoms. This selectivity is consistent with partial positive-charge stabilization in the transition state. The corresponding enyne ether products were isolated in 98–31% isolated yields, in most cases as a single regio- and E/Z stereoisomer (5 h at 45 °C, 5 mol% [FeCp₂][BF₄] catalyst load, six equivalents alcohol nucleophile). The ferrocenium-catalyzed cyclopropyl ring opening establishes a convenient method for accessing enyne motifs, which are important structural units in organic synthesis and medicinal chemistry. Full article

Bacteria pose significant threats to human health, industrial production, and daily life, with widespread microbial contamination remaining a critical challenge for global public health. Conventional porous materials often suffer from insufficient antibacterial efficacy, necessitating the development of advanced antimicrobial systems. Herein, we report a synthetic strategy for fabricating chloride-regenerable porous tubular polymers (HCP-DMH-Cl) via a combination of Friedel–Crafts alkylation and nucleophilic substitution reactions. HCP was initially prepared through a crosslinking reaction via Friedel–Crafts alkylation using FeCl₃ as the catalyst and benzyl alcohol as the monomer. SEM characterization was performed to validate the tubular architectural morphology of HCP. The polymeric N-halamine precursor, HCP-DMH, was subsequently obtained through stepwise bromomethylation and nucleophilic substitution modifications. Upon chlorination, HCP-DMH-Cl exhibited good antibacterial efficacy against both E. coli and S. aureus, coupled with favorable regenerability of its oxidative chlorine content. This approach paves the way for designing next-generation porous media with tailored antibacterial functionality and sustainable chlorine-release capabilities. Full article

The synthesis of nitrogen-containing heterocycles remains a subject of significant interest due to their applications in medicinal chemistry and materials science. This paper describes the preparation of imidazo[1,2-a]pyridine using a catalytic system consisting of the deep eutectic solvent (DES) choline chloride (ChCl)–tartaric acid (1:2) and I₂ by reaction between 2-aminopyridines and chalcones (1,3-diphenylprop-2-en-1-ones). The proposed mechanism suggests the activation of the chalcone carbonyl by the DES, enhancing the polarization of the conjugated system which suffers electrophilic addition by I₂ to the C=C bond. The resulting intermediate undergoes a nucleophilic attack by 2-aminopyridine followed by cyclization and iodine-promoted oxidation and aromatization to yield the corresponding imidazo[1,2-a]pyridine products. The role of the DES is crucial, as it facilitates carbonyl activation through hydrogen bond interactions, stabilizes reactive intermediates, and promotes protonation–deprotonation steps, thereby eliminating the need for metal catalysts or toxic organic solvents. Theoretical calculations at the PM6 level of theory suggest that the DES acts as a catalyst in this reaction, due to the nature of its components enabling the development of more sustainable synthetic strategies. Full article

Aliphatic polyesters, widely used in biomedicine due to their biocompatibility and biodegradability, are typically synthesized via the ring-opening polymerization (ROP) of cyclic esters. Although traditional metal catalysts are highly active, their biological toxicity limits their applications. Organocatalysts, particularly natural organic molecules, offer safer alternatives. We explored the ROP mechanisms of cyclic esters (L-Lactide (L-LA), ε-caprolactone (ε-CL), and δ-valerolactone (δ-VL)) catalyzed by phosphonium carboxybetaines (PCBs, (PhR)₃P⁺(CH₂)₂COO⁻, R = H(PCB), F(PCB-F) and OMe(PCB-OMe)) through density functional theory (DFT) computations. The DFT results revealed that the ROP of cyclic esters follows a bifunctional–cooperative activation mechanism, wherein the phosphonium moiety (Ph₃P⁺(CH₂)₂) activates the monomer via an extensive hydrogen-bonding interaction network, and the carboxylate (COO⁻) serves as a proton acceptor to enhance the nucleophilicity of the initiator phenylpropanol (PPA). In contrast, unsubstituted PCB exhibited the lowest energy barrier, being consistent with the highest catalytic activity among PCB derivatives observed experimentally. Moreover, a series of novel PCB derivatives (Ph₃P⁺(CH₂)_nCOO⁻, n = 3–6 (PCB1-PCB4)) were designed by regulating the carbon spacer length, and their catalytic performances were computationally tested. The designed catalyst PCB2 (Ph₃P⁺(CH₂)₄COO⁻) exhibited higher activity for the ROP of L-LA, attributed to providing sufficient flexibility to minimize deformation while improving proton-accepting capability. Similarly, PCB2 also demonstrated superior catalytic activity for δ-VL and the more challenging ε-CL monomer. This work not only clarifies the intrinsic catalytic nature of these zwitterionic organocatalysts, but also provides an effective strategy for the rational design of high-performance, metal-free catalysts for the synthesis of sustainable polyesters. Full article

While electrophilic substitution is used to attack positions 1(3) and possibly 2 of azulenes, nucleophilic substitution is often used to obtain azulenes with substituents at positions 6 or 4(8). The electrical charge at positions 2, 5, or 7 makes them unsuitable for electrophilic or nucleophilic substitution. Azulenes bearing substituents at these positions have been synthesized mainly by the building of the azulene skeleton or especially resorting to reactions catalyzed by metallic compounds. In this context, the proposed mini review will focus on some of the cases in which compounds with substituents in these positions are obtained by substitution without the intervention of a catalyst and are therefore advantageous from both an ecological and economic point of view. Full article

The synthesis, in particular the industrial production, of pharmaceuticals requires a broad arsenal of synthetic reactions capable of selectively forming specific structural motifs and assembling smaller building blocks into complex molecules. The Chan–Evans–Lam cross-coupling reaction, which forms a bond between a N-nucleophile and an aryl group from a boronic acid, catalysed by copper salts, is a typical example of this synthetic route. Considering the toxicity of copper and the stringent regulatory limits for its residues in final pharmaceutical products, a heterogeneous catalytic approach offers a viable alternative for this transformation. In this work, we present a simply and reproducibly synthesized catalyst based on copper nanoparticles supported on reduced graphene oxide (Cu-rGO), with high efficiency in a model Chan–Lam reaction involving benzimidazole and aniline derivatives with substituted boronic acids. Full article

Methylbutynol (MB) is a typical propargylic alcohol with both alkynyl and hydroxyl groups, featuring excellent modifiability and broad applications. Currently, it is produced through the reaction of alkaline metallic acetylides and acetone, requiring expensive raw material and harsh reaction conditions. Herein, a novel method was proposed by replacing the metallic acetylide with calcium carbide (CaC₂) as a low-cost industrial acetylide reagent. The effects of solvent, activator, and proton donor on the ball mill reaction, and the defoaming performance of the resultant MB and its oxidative coupling product (2,7-dimethyl-3,5-octadiyn-2,7-diol), were studied. Nucleophilic reactivity of CaC₂ with acetone can be regulated by the activating effect of the ball mill, an appropriate activator, and a proton donor. High yield of MB (~94%) was obtained under synergistic action of TBAF·3H₂O and acetylene, which represents a facile synthesis process of MB under mild conditions. MB exhibits good defoaming performance, and 2,7-dimethyl-3,5-octadiyn-2,7-diol is more promising, being an excellent non-ionic defoamer. The result is of great significance for exploring new chemical reactions of CaC₂ and its high-value utilizations. Full article

This paper demonstrates the successful synthesis of novel hybrid heterogeneous catalysts for the sustainable conversion of CO₂ into cyclic organic carbonates (COCs). The nanocat-alysts have been fabricated by encapsulating pre-formed ultra-small gold nanostructures into a nascent zinc-coordination polymer (ZnCP) framework formed from two organic building blocks, 2,4-naphthalenedicarboxylic acid (1,4-NDC) and 5-amino-1H-tetrazole (5-Atz), which serves as a nitrogen-rich ligand. Applying the fabricated catalysts in the synthesis of COCs yields high yields (up to 97%) and high selectivity (up to 100%), with exceptionally high turnover frequencies (TOFs) (up to 408 h⁻¹). The catalytic process can be carried out under mild conditions (80 °C, 1.5 MPa CO₂) and without the use of solvents. Nitrogen-rich ligand molecules in the structure of ZnCPs enhance catalytic performance thanks to additional nucleophilic centres, which are effective in the epoxides’ ring-opening process. The hybrid catalysts with encapsulated gold nanostructures, which modify the liquid–gas interface between epoxide and CO₂, give significantly higher yields and TOFs for less active epoxides. The designed hybrid nanocatalysts exhibit superior stability under the studied reaction conditions and can be reused without loss of activity. The developed coordination polymers are constructed from green components, and green chemistry principles are applied to prepare these catalytic materials. Full article

The efficient generation of structurally diverse rare ginsenosides from abundant precursors remains a significant challenge. In this study, a heterogeneous catalyst, 12-tungstosilicic acid supported on mesoporous silica (HSiW@mSiO₂), was developed for the transformation of ginsenoside Re in aqueous ethanol solution. The reaction was conducted under mild conditions, and the products were systematically analyzed using high-performance liquid chromatography coupled with multistage tandem mass spectrometry and high-resolution mass spectrometry. A total of 24 transformation products were identified, arising from deglycosylation, epimerization, dehydration, cyclization, and nucleophilic addition reactions. Structural elucidation revealed the formation of deglycosylated, hydrated and dehydrated derivatives, C-20 epimers, and novel ethoxylated protopanaxatriol-type ginsenosides resulting from solvent incorporation at the C-24(25) or C-20 position. Product distribution varied with reaction parameters, including solvent composition, reaction time, temperature, and catalyst dosage. The synthesized HSiW@mSiO₂ catalyst could be readily recovered by centrifugation and reused for five consecutive cycles, with complete conversion of ginsenoside Re maintained in the first two runs and a gradual decline in conversion to approximately 50% by the fifth cycle. This work demonstrates the efficacy of solid acid catalysts in enabling the structural diversification of ginsenosides through solvent-involved pathways. Full article

This study evaluates the feasibility of achieving chemoselective aldol reactions over competing Henry reactions and employs competition experiments to establish proof of concept. A typical reaction involved using in-water reaction conditions where a concentrated organic layer containing an aldol nucleophile (1.5 equiv), a Henry nucleophile (1.5 equiv), an aldehyde electrophile (1.0 equiv), and a proline-based amino acid catalyst (2.5 mol%) constituted one phase, while the second phase was water (15 equiv). Highly enantioenriched aldol products were formed in practical yields, and a variety of Henry nucleophiles (nitroalkanes, allylic nitro compounds, and ethyl nitroacetate) were tolerated. This systematic examination of nitro compounds (pK_a 5.5–10.0) established a pK_a of ≈7.0 as the critical threshold at which nitronate formation results in Henry product formation under catalysis with 1. Reactions alternatively performed in MeOH/H₂O (3:2 equiv) solvent combinations, at times, provided improved chemoselectivity or product dr over the use of water (15 equiv) alone but required longer reaction times to produce similar yields. Reactions constrained by solubility were investigated using mechanochemical methods, but these conditions failed to deliver practical yields of either competition product. In summary, defining this category of aldol chemoselectivity may provide new tactical opportunities for the synthesis of complex molecular targets. Full article

Our previously discovered marine natural products, peniterphenyls A and E, exhibit superior anti-herpes simplex virus 1/2 (HSV 1/2) activity, probably via interference with virus adsorption and membrane fusion to host cells. Their clear mechanism mode still remains unresolved due to its limited availability from nature. This study establishes their first site-selective chemical total syntheses, affording peniterphenyls A and E in overall yields of 4.5% (over thirteen steps) and 2.3% (over twelve steps), respectively. A nucleophilic aromatic substitution (S_NAr) between compounds 4 and 5, and a direct C(sp²)–H/C(sp²)–H oxidative coupling using the Pd(TFA)₂/AgOAc catalyst system with a pivaloyl directing group conveniently furnishes the dibenzofuran core with good efficiency. Steric hindrance and substituent directing effects of arene govern the high site-selectivity of the Pd-catalyzed C(sp²)–H activation during furan formation. Featuring readily available materials and straightforward operations, this synthetic route provides convenient access to these bioactive natural products for further study. Full article

Density functional theory (DFT) calculations at the M06-2X-D3/6-311++G(2df,2pd) level elucidate the mechanism and selectivity origins in the NHC-catalyzed divergent synthesis of spirocyclopentane oxindoles from isatin-derived enals and N-sulfonyl ketimines. The Michael addition constitutes the regio- and stereoselectivity-determining step, where Parr function analysis demonstrates that nucleophile/electrophile electrophilicity governs regioselectivity, while distortion/interaction and non-covalent interaction analyses reveal stereoselectivity is controlled by distortion and weak interactions. K₃PO₄ facilitates Breslow intermediate formation and proton transfer toward the β-lactam-fused spirocyclopentane oxindole, whereas N,N-diisopropylethylamine (DIPEA) promotes these processes for the spirocyclopentane oxindole bearing an enaminone moiety. Catalyst roles are also further delineated. Full article

Polysiloxanes are unique polymers used in medicine and materials science and are ideal for various modifications. Classic functionalization methods involve a covalent approach, but finer tuning of the properties of the final polymers can also be achieved through sub-sequent noncovalent modifications. This study introduces a fundamentally new approach to polysiloxane functionalization by incorporating cooperative noncovalent interaction centers: selenium-based chalcogen bonding donors and polyfluoroaromatic π-hole acceptors into a single polymer platform. We developed an efficient nucleophilic substitution strategy using poly((3-chloropropyl)methylsiloxane) as a platform for introducing Se-containing groups with polyfluoroaromatic substituents. Three synthetic approaches were evaluated; only direct modification of Cl-PMS-2 proved successful, avoiding catalyst poisoning and crosslinking issues. The optimized methodology utilizes mild conditions and achieved high substitution degrees (74–98%) with isolated yields of 60–79%. Comprehensive characterization using ¹H, ¹³C, ¹⁹F, ⁷⁷Se, and ²⁹Si NMR, TGA, and contact angle measurements revealed significantly enhanced properties. Modified polysiloxanes demonstrated improved thermal stability (up to 37 °C higher decomposition temperatures, 50–60 °C shifts in DTG maxima) and increased hydrophobicity (water contact angles from 69° to 102°). These systems potentially enable chalcogen bonding and arene–perfluoroarene interactions, providing foundations for materials with applications in biomedicine, electronics, and protective coatings. This dual-functionality approach opens pathways toward adaptive materials whose properties can be tuned through supramolecular modification while maintaining the inherent advantages of polysiloxane platforms—flexibility, biocompatibility, and chemical inertness. Full article