Furan Ring Opening Research Articles

Azide‐Induced Furan Ring Opening for the Synthesis of Functionalized Indoles

We explored the reactivity of various furans towards 2‐azidobenzaldehydes, heterocyclic azidoaldehydes, or substituted 2‐azidobenzyl alcohols to form 2‐(2‐azidobenzyl)furan derivatives, unveiling the remarkable compatibility of the azide group with conditions typical of Friedel‐Crafts reactions. Moreover, we demonstrated that compounds of this type can be successfully synthesized by diazotization/azidation sequence from 2‐(2‐aminobenzyl)furans bearing electron‐donating substituents, while effectively circumventing undesired side reactions. Additionally, we presented a synthetic methodology for the preparation of 2‐(2‐acylvinyl)indoles, that involves thermal generation of nitrenes to initiate furan ring opening. Remarkably, our approach entails a nonconjugated configuration of the azidoaryl group and the furan ring, setting it apart from classical indole syntheses. The broad applicability and high efficiency of our method, which utilizes readily available starting materials, underscore its versatility as a synthetic tool of significant promise.

Enhancing the ketonization efficiency of biomass through selective conversion of furanic compounds

Catalytic ketonization of biomass is an effective approach for the deoxygenation of bio-oil and the enrichment of high-purity ketone products. However, the bio-oil contains a large amount of furanic components with oxygenated side groups (e.g., furfural, furfuralcohol, etc.), which severely hinders the efficiency of the ketonization reaction. In response to this challenge, this study employed Pd-based catalysts for selective conversion of furfural into "keto-friendly" components, thereby mitigating their inhibitory effects. Initially, three morphologies of CeO2 (the main catalyst for ketonization) were selected to investigate their influence on furfural conversion. It was found that the products were mainly furfural (exceeding 86 %), with only up to approximately 13 % of "keto-friendly" products (mainly furans) detected, indicating that pure CeO2 exhibits a weak catalytic effect on the effective conversion of furfural. Compared with pure CeO2, the yield of "keto-friendly" products increased significantly when 1 wt% Pd was loaded, demonstrating the excellent catalytic performance of Pd in the effective conversion of furfural. Co-doping of Pd and Zr (5 wt%) on CeO2 further increased the "keto-friendly" products to 66 %, suggesting a synergistic effect of Pd and Zr. Mechanism analysis revealed that Pd promotes the formation of furans and benzenes by enhancing the decarbonylation of furfural and subsequent furan ring opening reactions, while the competing carbonyl hydrogenation pathway is weakened. The findings of this study will be beneficial for enhancing the biomass ketonization conversion, thereby providing valuable references for the high-value utilization of biomass.

One-Pot Stereoselective Synthesis of the Naphthofurano-Iminosugars via a [3 + 2] Cycloaddition Reaction.

This study presents the synthesis of novel naphthofurano-iminosugars (4) using 2,3-O-isopropylidene D-ribose tosylate (1a), anilines (2), and 1,4-benzoquinone (3a) as starting materials through key iminium ion/enamine intermediates via [3 + 2] cyclization reactions at room temperature. The reaction has unique regioselectivity and stereoselectivity with moderate to excellent yields. The adaptability of this method has been demonstrated using various substituted anilines, on which both electron-donating and electron-withdrawing groups were well employed in the reactions. Notably, the treatment of the fused multicyclic iminosugar 4 with TFA efficiently leads to an interesting unexpected pyridinium salt (8), possible via four sequential steps: deprotection of the 2,3-O-isopropylidene group, furan ring opening, dehydration condensation of the OH groups, and elimination of water.

Hydrogen spillover accelerates catalytic hydrolysis ring opening of furans to polyols and alkanes

Hydrogen spillover accelerates catalytic hydrolysis ring opening of furans to polyols and alkanes

Characterization of metabolic features and potential anti-osteoporosis mechanism of pinoresinol diglucoside using metabolite profiling and network pharmacology.

Eucommia cortex is the core herb in traditional Chinese medicine preparations for the treatment of osteoporosis. Pinoresinol diglucoside (PDG), the quality control marker and the key pharmacodynamic component in Eucommia cortex, has attracted global attention because of its definite effects on osteoporosis. However, the in vivo metabolic characteristics of PDG and its anti-osteoporotic mechanism are still unclear, restricting its development and application. Ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry was used to analyze the metabolic characteristics of PDG in rats, and its anti-osteoporosis targets and mechanism were predicted using network pharmacology. A total of 51 metabolites were identified or tentatively characterized in rats after oral administration of PDG (10 mg/kg/day), including 9 in plasma, 28 in urine, 13 in feces, 10 in liver, 4 in heart, 3 in spleen, 11 in kidneys, and 5 in lungs. Furan-ring opening, dimethoxylation, glucuronidation, and sulfation were the main metabolic characteristics of PDG in vivo. The potential mechanism of PDG against osteoporosis was predicted using network pharmacology. PDG and its metabolites could regulate BCL2, MARK3, ALB, and IL6, involving PI3K-Akt signaling pathway, estrogen signaling pathway, and so on. This study was the first to demonstrate the metabolic characteristics of PDG in vivo and its potential anti-osteoporosis mechanism, providing the data for further pharmacological validation of PDG in the treatment of osteoporosis.

Noble-Metal-Free Carbon Encapsulated CoNi Alloy Catalyst for the Hydrogenation of 5-(Hydroxymethyl) Furfural to Tetrahydrofurandiol in Aqueous Media.

The selective hydrogenation of 5-(hydroxymethyl)furfural (HMF) into 2,5-bis-(hydroxymethyl)tetrahydrofuran (BHMTHF) in flow reactor using water as a green solvent, has been achieved on a non-noble metal catalyst based on monodispersed CoNi alloy nanoparticles covered by a thin carbon layer. The alloyed catalyst containing CoNi (molar ratio 1 : 1) was prepared in a one-step synthesis following a hydrothermal method. Total conversion of HMF with 91 % selectivity to BHMTHF was achieved. The reaction network has been stablished, in which the carbonyl group of HMF is first reduced to alcohol giving the 2,5-bis-(hydroxymethyl)furan (BHMF) with an apparent activation energy of 25 KJ/mol, and then the double bonds of the furan ring are hydrogenated (apparent Ea=31 KJ/mol). Formation of byproducts, mainly proceed from furan ring opening and ring rearrangement processes of BHMF, promoted by water. BHMTHF resulted a compound highly stable under reaction conditions. The fixed bed flow reactor was maintained operational for 65 h without observing any loss of catalytic activity and selectivity.

Hydrodeoxygenation of mixtures of biomass-derived model compound oxygenates over Pt/HY catalysts

In this study, a systematic analysis of the effect of three biomass pyrolysis oxygenates, viz., acetic acid, cyclopentanone and furfural, on the hydrodeoxygenation (HDO) of guaiacol is performed. Bifunctional Pt/HY catalysts with different Si/Al ratios were screened for the HDO of guaiacol. Guaiacol conversion and the cyclohexane yield increased with the concentration of acid sites in the zeolites. The presence of acetic acid and cyclopentanone did not affect the guaiacol conversion and the product selectivity, while guaiacol conversion decreased significantly in the presence of furfural. The effects of temperature, reaction time, and the guaiacol-furfural molar ratio on the HDO of guaiacol were studied. The time evolution of products showed that the furan ring opening influences the conversion of guaiacol.Quantum chemicaldensity functional theorycalculations using individual and binary model compounds revealed the decrease in adsorption energy of guaiacol over Pt (111) in the presence of furfural.

Impact of amine functionalization on poly(furfuryl alcohol) properties

Polyfurfuryl alcohol (PFA) is a biobased thermoset with high stiffness. As carbonyls are formed via furan ring opening during polymerization, their inevitable presence was exploited to tune the PFA properties. Various diamines were employed to react with these carbonyls and consequence on thermal and mechanical properties were evaluated. Short and rigid diamines and long and flexible diamines were respectively selected for this functionalization. The more rigid amines lead to an increase of the Tg of the material compared to the pristine PFA but the ultimate properties were not particularly improved. Flexible polyetheramines such as Jeffamine D-2000 (J2000) combined with PFA allows the formation of a flexible elastomeric network (Tg = −44 °C) presenting high thermal stability due to the presence of the thermally stable furanic chains. For PFA/J2000 samples, a rigid crust is formed in oxidative conditions at T > 175 °C when the PFA content is relatively important (>50 % w/w). This phenomenon is massively impacting the ultimate mechanical properties and the thermal stability.

Iron-Catalyzed Synthesis of 2,5-dicarbonyl-3-ene-phosphates via Furan Ring Opening

Iron-Catalyzed Synthesis of 2,5-dicarbonyl-3-ene-phosphates via Furan Ring Opening

Improving gas separation performances of poly(furfuryl alcohol)-based carbon molecular sieve membrane by tuning furan ring opening and membrane structures

Carbon molecular sieve membranes (CMSMs) have exhibited significant potential in gas separation applications, particularly in the realm of hydrogen and carbon dioxide separation. Poly(furfuryl alcohol) (PFA) represents a cost-efficient and sustainable precursor utilized in the synthesis of CMSMs. Nonetheless, PFA-based CMSMs have exhibited suboptimal performance and frequently necessitate supplementary supporting layers. In the present investigation, we have explored various acids as catalysts for the in-situ self-polymerization of PFA. Our findings reveal that PFA membrane catalyzed by sulfuric acid exhibits the most favorable performance, yielding a hydrogen permeability of 1394.4 Barrer and a H2/CH4 selectivity of 404.1. These values exceed the Robeson upper limits established in 2019. The enhanced gas separation performance of the sulfuric acid catalyzed PFA-based CMSM could be attributed to the increased furan ring opening and higher polymerization degree achieved through this catalytic process. Furthermore, our investigation delved into the addition of poly(styrene-co-acrylonitrile) (SAN) into the PFA membrane, yielding a CMSM featuring both dense and porous layers. With the addition of 6 wt% SAN in PFA membrane, the resulting CMSM exhibited a hydrogen permeability of 3126.4 Barrer, underscoring the potential for high-performance CMSMs made from the economical PFA precursor. The optimization of the PFA polymerization process and the incorporation of SAN, hold the promise of further elevating the performance of PFA-based CMSMs, and these advancements will substantially contribute to the advancement of sustainable and efficient gas separation technologies.

Linear Scaling Relationships for Furan Hydrodeoxygenation over Transition Metal and Bimetallic Surfaces.

Brønsted-Evans-Polanyi (BEP) and transition-state-scaling (TSS) relationships have become valuable tools for the rational design of catalysts for complex reactions like hydrodeoxygenation (HDO) of bio-oil (containing heterocyclic and homocyclic molecules). In this work, BEP and TSS relationships are developed for all the elementary steps of furan activation (C and O hydrogenation and CHx -OHy scission, for both ring and open-ring intermediates) to oxygenates, ring-saturated compounds and deoxygenated products on the most stable facets of Ni, Co, Rh, Ru, Pt, Pd, Fe and Ir surfaces using Density Functional Theory (DFT) calculations. Furan ring opening barriers were found to be facile and strongly dependent on carbon and oxygen binding strength on the investigated surfaces. Our calculations suggest linear chain oxygenates form on Ir, Pt, Pd and Rh surfaces due to their low hydrogenation and high CHx -OHy scission barriers, while deoxygenated linear products are favoured on Fe and Ni surfaces due to their low CHx -OHy scission and moderate hydrogenation barriers. Bimetallic alloy catalysts were also screened for their potential HDO activity and PtFe catalysts were found to significantly lower the ring opening and deoxygenation barriers relative to the corresponding pure metals. The developed BEPs for monometallic surfaces can be extended to estimate the barriers on bimetallic surfaces for ring opening and ring hydrogenation reactions but fails to predict the barriers for open-ring activation reactions due to the change in transition state binding sites on the bimetallic surface. The obtained BEP and TSS relationships can be used to develop microkinetic models for facilitating accelerated catalyst discovery for HDO.

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli

Theoretical study on the degradation mechanism, kinetics and toxicity for aqueous ozonation reaction of furan derivatives

The compounds including furan-2,5-dicarboxylic acid (FDCA), 2-methyl-3-furoic acid (MFA), and 2-furoic acid (FA), containing Furan ring are considered to be possessing high ozone reactivity, although in depth studies of their ozonation processes have not been carried out yet. Hence, mechanism, kinetics and toxicity by quantum chemical, and their structure activity relationship are being investigated in this study. Studies of reaction mechanisms revealed that during the ozonolysis of three furan derivatives containing C=C double bond, furan ring opening occurs. At temperature (298 K) and pressure of 1 atm, the degradations rates of 2.22 × 103 M−1 s−1 (FDCA), 5.81 × 106 M−1 s−1 (MFA) and 1.22 × 105 M−1 s−1 (FA) suggested that the reactivity order is: MFA > FA > FDCA. In the presence of water, oxygen and ozone, the Criegee intermediates (CIs) as the primary products of ozonation would produce lower molecule weight of aldehydes and carboxylic acids by undergoing degradation pathways. The aquatic toxicity reveals that three furan derivatives play green chemicals roles. Significantly, most of the degradation products are least harmful to organisms residing in the hydrosphere. The mutagenicity and developmental toxicity of FDCA is minimum as compared to FA and MFA, which shows the applicability of FDCA in a wider and broader field. Results of this study reveal its importance in the industrial sector and degradation experiments.

Heterocyclic boronates as colorimetric and chemical sensors for dialkyltin derivatives

The relevance of recognition for diorganotin (IV) species has been increased due to biological and environmental issues. The development of molecules able to carry out the recognition process of diorganotin (IV) compounds by simple analytical techniques is an interesting research topic. This paper describes the synthesis of three heterocyclic boronates obtained by the reaction of one equivalent of 5-formyl-2-furanboronic acid with two equivalents of 2-aminophenol (1), 4‑hydroxy-3-aminobenzoic acid (2) or 4-nitro-2-aminophenol (3). Reactions resulted in a π-conjugated systems by the formation of two new six membered fused heterocycles since the furan ring opening, as corroborated by single X-ray diffraction analysis for compound 1. Compounds 1–3 are green-colored solids with melting points higher than 300 °C. A solvatochromic effect was observed having the absorption band maxima values between 525 and 600 nm. The presence of donor atoms (N, O) in the boronates allow the use as chemical sensors for dialkyltin derivatives (Me2SnO, Bu2SnO, Me2SnCl2, Bu2SnCl2) by UV–Vis and fluorescence techniques. The recognition process for dialkyltin derivates was detected by color changes in solution and even because the presence of a new absorption band in UV–Vis spectra which is shifted to 600 and 621 nm for compounds 1 and 2, respectively. Boronate 2 showed lower Limit Of Detection values (LOD) of 237 nM for Me2SnCl2 and 234 nM for Bu2SnCl2. Less affinity was noticed for trialkyl derivates ((CH3)3SnCl and (CH3)3SnOH).

Structural Variations in Biobased Polyfurfuryl Alcohol Induced by Polymerization in Water.

Poly(furfuryl alcohol) is a thermostable biobased thermoset. The polymerization of furfuryl alcohol (FA) is sensitive to a number of side reactions, mainly the opening of the furan ring into carbonyl species. Such carbonyls can be used to introduce new properties into the PFA materials through derivatization. Hence, better understanding of the furan ring opening is required to develop new applications for PFA. This article studies the structural discrepancies between a PFA prepared in neat conditions versus a PFA prepared in aqueous conditions, i.e., with more carbonyls, through NMR and MALDI ToF. Overall, the PFA prepared in water exhibited a structure more heterogeneous than the PFA prepared in neat conditions. The presence of ketonic derivatives such as enols and ketals were highlighted in the case of the aqueous PFA. In this line, the addition of water at the beginning of the polymerization stimulated the production of aldehydes by a factor two. Finally, the PFA prepared in neat conditions showed terminal lactones instead of aldehydes.

Catalytic C–H Alumination of Thiophenes: DFT Predictions and Experimental Verification

A computational model for the palladium-catalyzed C–H functionalization of thiophenes with aluminum hydride reagents has been developed. This model predicts that metalation should occur exclusively at the 2-position of the heterocycle. While related 2-metalated furans are known to undergo a ring-expansion reaction, further calculations suggest that the thiophene-derived organoaluminum compounds should be both kinetically and thermodynamically stable with respect to ring opening. This model is supported by experimental data. Selective C–H alumination of thiophene, 2-methylthiophene, 2-methoxythiophene, and benzothiophene was achieved using [Pd(PCy3)2] as a catalyst with loadings as low as 0.02 mol %. Even under extremely forcing conditions (200 °C) there was no evidence for a ring-opening event. The differences in selectivity between furan and thiophene systems are rationalized in terms of the stabilization of a key intermediate (and transition state) in the pathway for furan ring opening by a strong dative O→Al interaction.

Revealed pathways of furan ring opening and surface crosslinking in biobased polyfurfuryl alcohol

Poly(furfuryl alcohol) – (PFA) is a biobased thermoset known for its highly crosslinked structure. Bidimensional NMR (2D-NMR) was employed to give new insights on the complex structural organization in PFA with a special emphasis on the side structures resulting from furan ring-opening. Interestingly, the presence of aldehyde functions was for the first time clearly highlighted and quantified in PFA resins. Overall, the aldehydes account for about 20 % of the total carbonyls present in PFA. Results from HSQC and HMBC sequences allowed proposing two pathways for the furan ring opening reactions. The first one is an hydrolytic-ring opening leading to levulinic like species. The second one is rather an oxidative furan-ring opening leading to conjugated aldehydes. These conjugated aldehydes are prone to crosslink via Diel-Alder cycloadditions with furanic entities thus leading to crosslinking. At macroscopic scale, this newly proposed crosslinking pathway would explain the formation of the rigid shell formed at the external surfaces of PFA resins.

Density functional theory simulation of heterogeneous polymerization reactions during biomass hydrothermal carbonization

AbstractCarbonaceous microspheres formed through heterogeneous polymerization reactions during hydrothermal carbonization of biomass showed a considerable effect on the mass yield and physicochemical properties of hydrochar. In exploring the growth mechanism of carbonaceous microspheres, the heterogeneous polymerization reaction of four typical organic components (5‐hydroxymethylfurfural, furfural, phenol, and p‐xylene) with the surficial functional groups of carbonaceous microspheres was investigated using density functional theory (DFT). Nucleophilic addition and dehydration are the main forms of polymerization reactions, and the former shows a lower reaction energy barrier than the latter by 100 kJ/mol, indicating that the nucleophilic addition reactions likely occur compared to dehydration reactions. And phenol likely promotes the growth of microspheres. In addition, the surficial furan ring structure of carbonaceous microspheres opened through ring opening, hydrogen atom transfer, and molecular space structure conversion in sequence. Among these reaction steps, the furan ring opening through hydration was the rate‐limiting reaction step, which showed the highest energy barrier with a value of 394.51 kJ/mol. However, the ring opening of furan rings could form more active sites, such as carbonyl groups, for subsequent polymerization reactions, indicating an increased potential for further reactions with aqueous‐phase organic components.

Furan ring opening reaction for the synthesis of 2,5-dicarbonyl-3-ene-phosphates.

Furan ring opening reactions are essential in organic synthesis, enabling the incorporation of diverse functional groups and the construction of complex molecular structures. A highly efficient and practical method for synthesizing 2,5-dicarbonyl-3-ene-phosphates from readily available biomass furan and dialkyl phosphonates is reported. The reaction, catalyzed by FeCl3, demonstrated wide substrate scope and high synthetic efficiency. Gram-scale synthesis was achieved, and a one-pot reaction provided a quick access route to the desired compounds. Additionally, a successful Diels-Alder reaction highlighted the versatility of the methodology.

Production of green jet fuel from furanics via hydroxyalkylation-alkylation over mesoporous MoO3-ZrO2 and hydrodeoxygenation over Co/γ-Al2O3: Role of calcination temperature and MoO3 content in MoO3-ZrO2

Green biofuels are equivalent to hydrocarbon-based motor fuels and compatible with existing refinery infrastructures and combustion engines. Therefore, sustainable production of green biofuels is essential to circumvent the construction of expensive biorefinery infrastructures. This study thus presents the production of green jet fuel from biomass-derived furanic compounds via hydroxyalkylation-alkylation (HAA) reaction coupled with hydrodeoxygenation (HDO) of the C15 biofuel precursor. MoO3-promoted ZrO2 is a promising solid acid catalyst with excellent thermal stability. The HAA reaction of 2-methylfuran with furfural was thus investigated over a novel MoO3-promoted mesoporous ZrO2 catalyst. This work elucidated the role of calcination temperature and MoO3 loading on the structural variation of MoO3-promoted mesoporous ZrO2 and the evolution of acid sites. The highest acid density and consequently best catalytic performance was observed at 873 K calcination temperature with 20 wt% MoO3 loading. About 85 % 2-methylfuran conversion was achieved over 1.25 g of this optimum catalyst at 2:1 2-methylfuran/furfural mole ratio, 323 K, and 5 h. The HAA reaction was further investigated at various reaction temperatures, catalyst loadings, and 2-methylfuran/furfural mole ratios to obtain optimum reaction conditions. HDO of biofuel precursor was examined over Co/γ-Al2O3 catalyst at various reaction temperatures, initial hydrogen pressure, and Co metal loading on γ-Al2O3 to understand the reaction mechanism and identify the optimum reaction conditions. HDO of biofuel precursor progressed through successive furan ring saturation and opening reactions, followed by a combination of HDO, decarbonylation, and cleavage of tertiary-carbon bonds. C9-C15 alkanes were observed as products, with C11 and C14 hydrocarbons being dominant at 573 K and 30 bar. The elevated hydrogen pressure and reaction temperature boosted the conversion of oxygen-containing intermediate compounds at the cost of CC cracking reactions. The conversion of oxygen-containing intermediate compounds was enhanced with rising Co metal loading on γ-Al2O3 up to 20 wt% due to the enhancement of metal dispersion.