Furan Ring Opening Research Articles

Ruthenium and Formic Acid Based Tandem Catalytic Transformation of Bioderived Furans to Levulinic Acid and Diketones in Water

AbstractEfficient tandem catalytic transformations of bioderived furans, such as furfural, 5‐hydroxymethylfurfural (5‐HMF), and 5‐methylfurfural (5‐MF), to levulinic acid (LA) and diketones, 1‐hydroxyhexane‐2,5‐dione (1‐HHD), 3‐hydroxyhexane‐2,5‐dione (3‐HHD), and hexane‐2,5‐dione (2,5‐HD), was achieved by using water‐soluble arene–RuII complexes, containing ethylenediamine‐based ligands, as catalysts in the presence of formic acid. The catalytic conversion of furans depends on the catalyst, ligand, formic acid concentration, reaction temperature, and time. Experimental evidence, including time‐resolved 1H NMR spectral studies, indicate that the catalytic reaction proceeds first with formyl hydrogenation followed by hydrolytic ring opening of furans. The ruthenium–formic acid tandem catalytic transformation of fructose to diketones and LA was also achieved. Finally, the molecular structures of the four representative arene–RuII catalysts were established by single‐crystal X‐ray diffraction studies.

Monitoring conical intersections in the ring opening of furan by attosecond stimulated X-ray Raman spectroscopy.

Attosecond X-ray pulses are short enough to capture snapshots of molecules undergoing nonadiabatic electron and nuclear dynamics at conical intersections (CoIns). We show that a stimulated Raman probe induced by a combination of an attosecond and a femtosecond pulse has a unique temporal and spectral resolution for probing the nonadiabatic dynamics and detecting the ultrafast (∼4.5 fs) passage through a CoIn. This is demonstrated by a multiconfigurational self-consistent-field study of the dynamics and spectroscopy of the furan ring-opening reaction. Trajectories generated by surface hopping simulations were used to predict Attosecond Stimulated X-ray Raman Spectroscopy signals at reactant and product structures as well as representative snapshots along the conical intersection seam. The signals are highly sensitive to the changes in nonadiabatically coupled electronic structure and geometry.

Gold catalyzed intramolecular hydroalkoxylation assisted ring opening of furans to the corresponding saturated γ-keto esters

A facile ring opening of furans in furyl propargyl alcohols to the corresponding saturated γ-keto esters is observed in the gold(III) chloride catalyzed reaction with MeOH. It is found that the ring opening of furan is driven by the intramolecular hydroalkoxylation. Mitigating the intramolecular hydroalkoxylation led to the expected conjugated enyne resulting from the dehydration.

ChemInform Abstract: Furan′s Gambit: Electrophile‐Attack‐Triggered Sacrifice of Furan Rings for the Intramolecular Construction of Azaheterocycles

AbstractReview: [recent studies on intramolecular furan ring opening — azaheterocycle ring closure reactions induced by acid or electrophilic attack on the furan ring; 57 refs.

On the Rational Design of Zeolite Clusters

We have applied density functional theory calculations to systematically investigate zeolite cluster-size convergence for two acid-zeolite-catalyzed processes related to the conversion of biomass: (1) the keto–enol tautomerization of acetone in HZSM-5 and HY and (2) the protonation and ring opening of furan in HZSM-5. We have used these reactions as platforms to study two different approaches for constructing successively larger cluster models of zeolites, with the aim of determining a protocol that converges the energy differences with minimal system size. One approach for cluster design involves counting framework bonds from the Brønsted acid-site aluminum atom. Another approach involves applying multicentered spherical cutoffs based on geometries of the zeolite active site, the adsorbed reactant, and the adsorbed product. We have investigated the convergence of reaction energies using single-point calculations on clusters containing as many as 166 tetrahedral (T) atoms and geometry optimizations on clusters with as many as 78 T atoms. For all reactions studied, convergence rates of single-point reaction energies agree well with those from geometry-optimized clusters. In addition, converged and optimized reaction energies agree well with previously published values for all reactions. Our central finding is that clusters generated with multicentered spherical cutoffs yield converged reaction energies with smaller system sizes than clusters generated by counting framework bonds. This method, employing a single length scale (5 Å), converges reaction energies with respect to system size to within chemical accuracy (±1 kcal/mol), and it includes between 15 and 34 T atoms in the cluster depending on the process and zeolite framework under investigation. We suggest a general protocol for generating such clusters for subsequent use in computational studies of zeolites and other heterogeneous catalysts.

Ring Activation of Furanic Compounds on Ruthenium-Based Catalysts

We employed a combination of isotopic labeling experiments, density functional theory calculations, and first-principles microkinetic modeling to investigate the mechanism of H/D exchange of furanic platform molecules. Alkylated furans (e.g., 2-methylfuran (2-MF)) exhibit appreciable H/D exchange, but furan and oxygenated furanics (e.g., furfuryl alcohol) do not. Detailed mass fragmentation pattern analysis indicates H/D exchange only occurs at unprotected α-carbons. Simulations show that, in the presence of coadsorbed toluene (solvent), the most likely pathway involves Ru surface mediated scission of the C–O bond in the furan ring at the unsubstituted carbon atom, followed by dehydrogenation, deuteration, and ring-closure steps. The degree of H/D exchange reaction depends mainly on the adsorption strength of exchange intermediates: strongly bound compounds, e.g., furan and furfuryl alcohol, inhibit H/D exchange via site blocking and slow desorption, whereas alkylated furans are sterically repelled by the solvent freeing up catalyst sites for exchange at the unsubstituted α-carbon of the furan ring. The binding strength of exchange intermediates is governed by interaction of the substituent group both with the surface and with the coadsorbed solvent molecules. The proposed H/D exchange mechanism on metal catalysts, which involves the opening of furan ring, is in stark contrast to the Brønsted catalyzed ring activation and suggests a possible pathway for the formation of ring-opening products and for rational selection of solvents.

ChemInform Abstract: A Simple Route to Polysubstituted Indoles Exploiting Azide Induced Furan Ring Opening.

AbstractAn efficient indole synthesis based on thermolysis of 2‐(2‐azidobenzyl)furans (III) and (VI) with attack of the formed nitrene moiety onto the ipso position of furan ring is developed.

Access to polysubstituted indoles or benzothiophenes via palladium-catalyzed cross-coupling of furfural tosylhydrazones with 2-iodoanilines or 2-iodothiophenols.

Palladium-catalyzed cross-coupling of furfural tosylhydrazones with 2-iodoanilines or 2-iodothiophenols produces polysubstituted indoles or benzothiophenes, respectively. The reaction proceeds through 2-furylmethylene palladium iodide intermediates, which undergo furan ring opening followed by ring closure to form indoles or benzothiophenes. This reaction will expand the synthetic applications of furfural derivatives.

Hydrogenation/Hydrolytic Ring Opening of 5-HMF by Cp*-Iridium(III) Half-Sandwich Complexes for Bioketones Synthesis

A new method for one-step synthesis of ketones from biobased 5-hydroxymethylfurfural (5-HMF) and its derivatives is reported. Bipyridine coordinated Cp*-Iridium(III) complexes (Cp*, 1,2,3,4,5-pentamethylcyclopenta-1,3-diene) exhibit highly efficient catalytic performance for hydrogenation/hydrolytic ring opening of 5-HMF and derivatives to produce ketones. The catalytic mechanism is proposed to proceed via carbonyl hydrogenation, hydroxyl group promoted and directed hydrolytic furan ring opening, followed by hydrogenation of α,β-unsaturated carbonyl compound based on the experimental and independent events’ statistical calculation results.

Ring-Opening and Oxidation Pathways of Furanic Oxygenates on Oxygen-Precovered Pd(111)

The surface reactivity of furan, furfural, and furfuryl alcohol on oxygen-precovered Pd(111) (O/Pd(111)) was studied via temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) to understand the oxidation processes of more complex alcohols and aldehydes. The primary reaction pathway explored was furfuryl alcohol dehydrogenation to furfural, followed by decarbonylation to furan and subsequent ring opening of furan through O–Cα scission; however, furfuryl alcohol and furfural also underwent other parallel reactions. At high coverages, deoxygenation of furfuryl alcohol to methylfuran was observed simultaneously with furfural production near 320 K, possibly through a disproportionation reaction of two alcohol adsorbates. Observation of furfural as a reaction product at this temperature was related to an increased prevalence of a weakly bound η1(O) aldehyde state near 250 K on O/Pd(111) as compared to clean Pd(111). Furfural also reacted with surface O to produce ...

Isolation and characterization of luminescent bicyclic boronates based on furan ring-opening reactions from 5-formyl-2-furanboronic acid

A new family of luminescent boronates was prepared from reaction of 5-formyl-2-furanboronic acid with 2-aminophenol derivatives. The furan ring-opening was favored by the presence of the boronic acid group. Evaluation of the photophysical characteristics for all compounds showed significant solvatochromic, fluorescent, and NLO properties.

Conversion of 2-furylcarbinols with alkyl or aryl azides to highly functionalized 1,2,3-triazoles via cascade formal [3 + 2] cycloaddition/ring-opening.

A Lewis acid promoted cascade cycloaddition/ring-opening of 2-furylcarbinols with alkyl or aryl azides is described. The reaction features an initial formal [3 + 2] cycloaddition to form a trisubstitued triazole motif, followed by a ring opening of furan to generate the (E)-configuration of the enone. A wide range of highly functionalized triazoles is expediently and efficiently synthesized in a highly step-economical manner.

Titanium hydrogenphosphate: An efficient dual acidic catalyst for 5-hydroxymethylfurfural (HMF) production

Dual Brønsted and Lewis acidity of solid acid catalysts enhances selective production of 5-hydroxymethylfurfural (HMF). This report describes a simple template-free synthetic approach for the preparation of titanium hydrogenphosphate (TiHP) material containing Lewis and Brønsted acid sites. As-synthesized material has been thoroughly analyzed by several analytical methods for elucidating its structural properties, including determination of the presence of Brønsted acidic phosphate group and measurement of total acid density. NH3-TPD data reveals high surface acidity (1.43mmolg−1) of the TiHP, which is indeed reflects to its catalytic effectiveness for the conversion of fructose, giving 55% HMF in biphasic solvent. Glucose conversion gives better yield (35%) when the reaction was carried out in a larger reactor (2L Parr reactor), which might be due to better mechanical stirring and hence higher mixing efficiency of the reactants. Brønsted acid sites in the catalyst facilitated the formation of furan ring opening product, levulinic acid, at higher temperatures. The catalyst shows excellent recyclability and the recovered catalyst after the 3rd cycles retained XRD and TGA characteristics.

A simple route to polysubstituted indoles exploiting azide induced furan ring opening.

A straightforward, efficient indole synthesis based on thermolysis of 2-(2-azidobenzyl)furans with attack of the formed nitrene moiety onto the ipso position of furan ring has been developed. The cyclization is accompanied by furan ring opening and affords indoles with a 2-acylvinyl substituent suitable for further modifications.

Vapor phase hydrogenation of 2-methylfuran over noble and base metal catalysts

Vapor phase hydrogenation of 2-methyl furan (2-MF) was carried out over barium-promoted copper chromite (Ba/Cu/Cr), Cu/Cr/Ni/Zn/Fe, Cu-Ru/C, 0.5wt.% Pt/C (Pt/C), and 0.5wt.% Pd/C (Pd/C) catalysts, respectively. The catalysts were characterized with respect to their specific surface areas by the N2 BET method and solid-state structures by X-ray diffraction (XRD). The XRD data confirmed the formation of a mixed oxide in the copper-chromite catalyst and the presence of small Pt and Pd crystals (<5nm by TEM) in the carbon-supported catalysts. The 2-MF hydrogenation was performed in vapor phase at atmospheric pressure in a continuous flow fixed bed tubular reactor at 140–350°C employing the H2/2-MF mole ratios in the 10–25 range. The results of 2-MF hydrogenation showed that the Ba/Cu/Cr, Cu/Cr/Ni/Zn/Fe, Cu-Ru/C and Pt/C catalysts were mainly active for furan ring opening leading mostly to 2-pentanone (2-PN) as well as small amounts of other products, such as 2-methyltetrahydrofuran (2-MTHF), 2-pentanol (2-PL), 1-pentanol (1-PL) and cracked hydrocarbons (butane and propane). On the other hand, the Pd/C catalyst was highly selective in 2-MF ring saturation leading to 2-MTHF as the main product below 220°C, whereas it became increasingly selective to 2-PN, the ring opening product, at higher temperatures.

A DFT study of furan hydrogenation and ring opening on Pd(111)

The reaction energies and the corresponding energy barriers of hydrogenation and ring opening of furan on Pd(111) for the formation of tetrahydrofuran (THF), 1-butanol and small hydrocarbons were studied using density functional theory (DFT). THF forms via sequential hydrogenation of carbon atoms of the furan ring in the order of α-carbon, adjacent β-carbon, second β-carbon, and the remaining α-carbon. Upon hydrogenation of the α-carbon of furan, ring opening becomes facile. Thus, hydrofuran (HF) is a reactive intermediate in both hydrogenation and ring opening. The fate of HF determines the selectivity of the overall reaction. A simple kinetic analysis indicates that coverage effects are important and the hydrogen partial pressure is a key factor in controlling selectivity. Dihydrofuran (DHF) was found to be a stable intermediate, consistent with experimental findings. Once DHF is formed, ring opening is not favored due to the high energy barriers of ring opening of DHF, trihydrofuran (TriHF) and THF. 1-Butanol is a thermodynamically favored product, while THF is kinetically preferred. Our theoretical work agrees well with experimental observations that 1-butanol is a major product at high temperatures whereas THF is a major product at low temperatures. Insights gained into selectivity toward ring hydrogenation and ring opening can assist future studies in catalyst selection.

Diminishing hazardous air pollutant emissions from pyrolysis of furan no-bake binders using methanesulfonic acid as the binder catalyst

The formation of hazardous air pollutants (HAPs) in thermal decomposition of furan no-bake foundry binders was investigated using analytical pyrolysis techniques. Two furan binders cured with p-xylenesulfonic acid (conventional acid catalyst used in foundries) and methanesulfonic acid (alternative catalyst proposed for diminishing HAPs) were flash pyrolyzed in a Curie-point pyrolyzer at 920 °C and slowly pyrolyzed in a thermogravimetric analyzer from 50 to 800 °C with a heating rate of 20 °C min−1. Similar HAPs (mainly benzene, toluene, and xylenes) were identified in the emissions of the two binders. However, the HAP yields were much higher for the binder cured with p-xylenesulfonic acid than for the binder cured with methanesulfonic acid (3.74 and 1.24 mg HAPs/g binder pyrolyzed, respectively). By analyzing the HAP formation pathways, it was concluded that for the binder cured with p-xylenesulfonic acid, the aromatic HAPs were originated mainly from the acid catalyst. In addition, some HAPs (predominantly benzene) could be formed from the recombination of furan-derived fragments (e.g., C2–C4 radicals generated from ring-opening of furans). The results suggest that by replacing the conventionally used catalysts (arylsulfonic acids) with methanesulfonic acid, the HAP emissions from furan no-bake molds can be decreased significantly in metal casting processes.

ChemInform Abstract: Furan Ring Opening‐Pyrrole Ring Closure. A Simple Route to 1,2,3,4‐Tetrahydropyrrolo[1,2‐a]pyrazin‐3‐ones.

AbstractA simple and efficient approach to convert furfurylamines into the title compounds (IV) via acylation, deprotection, furan ring opening, and Paal—Knorr cyclization sequence is developed.

Synthesis of bis-benzoquinoline derivatives catalyzed by iodine via ring-opening of furan

A three-component reaction of aromatic aldehyde, naphthalene-2-amine, and tetrahydro-2,5-dimethoxyfuran in methanol catalyzed by iodine, is described in this paper. With the ring-opening of furan, a series of 3-aryl-2-(3-arylbenzo[f]quinolin-2-yl)benzo[f]quinoline derivatives were obtained in moderate yields.

An entry to polysubstituted furans via the oxidative ring opening of furan ring employing NBS as an oxidant

A class of polysubstituted functionalized furans was synthesized efficiently starting from readily available furans involving the oxidative ring opening of the furan rings using NBS as an oxidant. The reaction proceeded through a sequence of oxidative dearomatization of the furan ring/spirocyclization/aromatization.