Diels-Alder Condensation Research Articles

Tuning the selectivity on the furan-propylene Diels-Alder condensation over acid catalysts: Role of pore topology and surface acidity

This work is focused on obtaining aromatics from renewable resources by propylene-furan Diels-Alder condensation. Several acid catalysts with different pore topology and SiO2/Al2O3 ratios were considered to gain further understanding of the molecular sieve and acidity effects on the selectivity towards different fractions and the catalytic stability. Experiments were performed in a fixed bed reactor at 500 ºC, WHSV = 17.4 h−1 and 3:1 propylene:furan molar ratio. Small pore-size materials (CHA, FER, MOR) are mainly selective to alkenes following cracking and oligomerization pathways, whereas materials with a larger pore size (FAU, MCM-41) produce polycyclic compounds and coke precursors. BEA and mainly MFI zeolites have the optimum topology to produce aromatics, mainly toluene. Experimental results suggest a competition between condensation and alkylation, the first one being promoted by the strongest acidic sites. These data provide the basis of a comprehensive reaction mechanism that allows anticipating the product distribution as a function of the catalytic properties of the considered material.

From Biomass to Green Aromatics: Direct Upgrading of Furfural–Ethanol Mixtures

This work demonstrates that the production of aromatics by gas-phase Diels–Alder condensation of biomass platform molecules (furfural and ethanol) is feasible in the same terms as using chemicals from a petrochemical origin or more complex preparation procedures (as ethylene or furan). Thus, a double benefit for the environment is obtained since a waste biomass is proposed as the raw material to produce industrial high-value products by a renewable route. Experimental results with acid zeolites (ZSM-5) at 500 °C reveal total conversion and aromatic selectivities >42% (mono and bicyclic ones), with a similar catalytic stability to the most widely studied furan–ethylene system, a clear consequence that the furfural oligomerization is prevented by the prevalence of a Diels–Alder mechanism.

Role of Reactant Alkylation Grade in the Selectivity and Stability of Furan–Alkene Diels–Alder Reactions

Diels–Alder condensation between different bio-based furanic compounds and light alkenes was performed in a fixed-bed reactor using ZSM-5 zeolite as a catalyst, analyzing the role of the alkylation of both reactants in this gas-phase reaction. The effect of this alkylation on product distribution and catalyst stability was thoroughly studied. These two aspects are the critical drawbacks in the production of aromatics from biomass-derived carbonylic compounds. The use of alkylated furans and alkenes promotes monoaromatic formation and their subsequent alkylation, minimizing the production of secondary condensation byproducts, such as naphthalenes and coke. This fact significantly improves the stability of the aromatic production without affecting the regeneration capacity of the zeolite. The methylfuran–propylene system is proposed as the most promising one for this purpose, increasing the selectivity to benzenes by 22% and the stability by 77%, concerning the results obtained with the methylfuran–ethylene system.

Benzofuran as deactivation precursor molecule: Improving the stability of acid zeolites in biomass pyrolysis by co-feeding propylene

Benzofuran (BZF) is produced during the biomass and waste pyrolysis, playing a key role in the catalytic deactivation in the processing of the resulting fractions, as well as in catalytic pyrolysis reactions. The transformation of this chemical over a typical pyrolysis catalyst (ZSM-5) is studied in this article. When this compound is processed alone, it presents a very high reactivity. At low temperature, the formation of large amount of coke precursors leads to a fast catalyst deactivation. As temperature increases, the weight of cracking reactions (yielding benzenes or naphtalenes) becomes more important, increasing the catalyst’s stability, although new polyaromatic carbon species are detected.A new strategy to minimize the deactivation caused by this compound, consisting of co-feeding propylene, is proposed. The presence of an alkene leads to the formation of alkylated derivatives of Diels-Alder condensation products, hindering their oligomerization capacity and minimizing the formation of polyaromatic coke deposits. Different temperatures and alkene/BZF ratios were tested, concluding that increasing the alkene concentration and the reaction temperature monotonously increase the catalyst’s stability in presence of BZF.

Catalytic Copyrolysis of Lignocellulose and Polyethylene Blends over HBeta Zeolite

Coprocessing of Eucalyptus woodchips (EU) and low-density polyethylene (LDPE) has been investigated using two HBeta zeolites as catalyst. The reactions were carried out in a two-step (thermal/catalytic) system, varying the catalyst to feed (C/F) ratio. A maximum in the yield of the liquid organic fraction (oil*) was observed for both HBeta samples at intermediate C/F ratios due to the occurrence of sequential cracking reactions, which were accompanied by a significant reduction of the oil* oxygen content. This finding, together with the results obtained when feeding pure EU and LDPE, denotes that remarkable synergistic effects occur during the coprocesssing of lignocelllulosic biomass and polyolefinic plastics over HBeta zeolite, mainly by Diels–Alder condensation between furans and light olefins. The presence of acid sites with moderate strength in the HBeta samples is an essential factor to obtain high oil* yields since it limits the extension of severe cracking reactions.

A Practical General Method for the Preparation of Long Acenes.

The field of long acenes, the narrowest of the zig-zag graphene nanoribbons, has been an area of significant interest in the past decade because of its potential applications in organic electronics, spintronics and plasmonics. However the low solubility and high reactivity of these compounds has so far hindered their preparation on large scales. We report here a concise strategy for the synthesis of higher acenes through Diels-Alder condensation of arynes with a protected tetraene ketone. After deprotection by cleavage of the ketal, the obtained monoketone precursors cleanly yield the corresponding acenes through quantitative cheletropic thermal decarbonylation in the solid state, at moderate temperatures of 155 to 205 °C. This approach allows the preparation of heptacene, benzo[a]hexacene, cis- and trans-dibenzopentacene and offers a valuable new method for the synthesis of even larger acenes.

Mechanisms of thermal decomposition of cyclodiene pesticides, identification and possible mitigation of their toxic products

Abstract Mechanisms of pyrolysis of several representative cyclodiene pesticides, viz., dieldrin, aldrin and isodrin, have been studied by quantum chemical techniques and dieldrin and isodrin have been subjected to experimental pyrolysis investigation. Comparison is made with earlier studies on another cyclodiene - endosulfan. Cyclodienes which are initially produced by Diels-Alder condensation of hexachlorocyclopentadiene (HCCP) and a substrate, initially decompose by retro Diels-Alder reaction back into HCCP and the substrate, both of which undergo further reaction. In the case of dieldrin, pyrolysis is initiated at 673 K and the substrate, norbornadiene oxide, further decomposes to produce CO and benzene which are observed experimentally. Above ∼800 K hexachlorocyclopentadiene undergoes rapid Cl bond fission and Cl atoms abstract H atoms from dieldrin forming HCl and lead to four different types of dieldrin radicals, just one of which can undergo a sequence of reactions of modest energy barriers to lead to the major observed high temperature products, pentachlorostyrene, hexachlorostyrene and polychlorinated benzenes. In contrast to other cyclodienes, pyrolysis of isodrin which is initially produced by Diels-Alder condensation of hexachloronorbornadiene and cyclopentadiene does not undergo initial retro Diels-Alder decomposition, instead undergoing an intramolecular rearrangement to a “birdcage” structure which eventually decomposes to HCl and aromatic soot precursors. A simple relationship between the rate constants for retro Diels-Alder decomposition and Cl fission of HCCP is discussed to evaluate whether cyclodiene-contaminated soils might be remediated via thermal desorption.

Total Synthesis of γ-Indomycinone and Kidamycinone by Means of Two Regioselective Diels-Alder Reactions.

An efficient access for the synthesis of pluramycinones is described. Total syntheses of racemic γ-indomycinone and kidamycinone were achieved by means of two Diels-Alder reactions. A first Diels-Alder condensation followed by a Stille cross-coupling is used for the elaboration of the desired substituted dienes which will be involved in the second pericyclic reaction with juglone to construct the tetracyclic core of pluramycinones.

Multicomponent Condensation Reactions via ortho-Quinone Methides.

Iron(III) salts promote the condensation of aldehydes or acetals with electron-rich phenols to generate ortho-quinone methides that undergo Diels-Alder condensations with alkenes. The reaction sequence occurs in a single vessel to afford benzopyrans in up to 95% yield. The reaction was discovered while investigating a two-component strategy using 2-(hydroxy(phenyl)methyl)phenols to access the desired ortho-quinone methide in a Diels-Alder condensation. The two-component condensation also afforded the corresponding benzopyran products in yields up to 97%. Taken together, the two- and three-component strategies using ortho-quinone methide intermediates provide efficient access to benzopyrans in good yields and selectivities.

Sulfones in heterocyclic synthesis: advances in the chemistry of phenyl sulfonylacetophenone

The present review provides a survey on the structural features, synthetic methodologies, and reactions of phenyl sulfonylacetophenone, considered to be one of the most important synthons in the field of synthetic organic chemistry. β-Ketosulfone is an active C–H acid which has been widely used as a nucleophile in many organic transformations. It has been used for synthesis of five- and six-membered ring systems containing one or two heteroatoms. In addition, it has been used as a starting material for synthesis of fused heterocycles, cyclopropane, cyclopentene, and cyclohexanone derivatives. β-Ketosulfone has been used for synthesis of γ- and δ-ketosulfones, 1,4-diketones, amides, ethers, and substituted benzene derivatives due to its high synthetic importance. It is a reactive intermediate in electrophilic reactions such as halogenation, alkylation, arylation, heteroarylation, and coupling reactions, and is involved in other types of reaction such as Diels–Alder condensation with aldehydes and desulfonylation. The mechanistic pathways of these reactions and their important synthetic applications are discussed herein.

Identification of Marbon in the Indiana Harbor and Ship Canal

Marbon is isomeric with Dechlorane Plus (DP). Both are produced by the Diels-Alder condensation of hexachlorocyclopentadiene with cyclic dienes, and both have elemental compositions of C18H12Cl12. Dechlorane Plus is commonly found in the environment throughout the world, but Marbon has, so far, only been detected at low levels in one sediment core collected near the mouth of the Niagara River in Lake Ontario. Here we report on the concentrations of Marbon and anti-DP in 59 water samples from five Lake Michigan tributaries [the Grand, Kalamazoo, St. Joseph, and Lower Fox Rivers, and the Indiana Harbor and Ship Canal (IHSC)], 10 surface sediment samples from the IHSC, and 2 surface sediment samples from the Chicago Sanitary and Ship Canal. Three Marbon diastereomers were detected in the water and sediment samples from the IHSC, which is far from the location of its previous detection in Lake Ontario. The sum of the concentrations of the three Marbons was greater in the water from the IHSC (N = 11, median =150 pg/L) compared to those in water from the other four tributaries (N = 11-13, medians =0.9-2.0 pg/L). Marbon concentrations in sediment samples from the IHSC were up to 450 ng/g dry weight. Anti-DP was also measured for comparison. Its concentrations were not significantly different among the water samples, but its sediment concentrations in the IHSC were significantly correlated with those of Marbon. The source of Marbon contamination in the IHSC is not clear.

Synthesis and investigation of bromine containing oxy- and propionoxyphenylimides for polymers thermostabilization

ABSTRACTThe new bromine containing oxyphenylimides are synthesized by Diels-Alder condensation from commercial products. From the bromine containing oxyphenylimides were obtained corresponding imidophenylpropionates. The brominating of oxyphenylimides has different influence on their thermal properties subject to diene building. The possible routes of thermal decomposition of the brominated oxyphenylimides and imidophenylpropionates were studied with the help of thermal desorption analysis coupled with mass spectrometry. The perspectives of bromine containing oxyphenylimides usage for creation of new polystyrene stabilizing systems are discussed.

A combined experimental and density functional study of 1-(arylsulfonyl)-2-R-4-chloro-2-butenes reactivity towards the allylic chlorine

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring-substituted 1-(arylsulfonyl)-2-R-4-chloro-2-butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1-arylsulfonyl 1,3-butadienes (48–95%), 1-(arylsulfonyl)-2-R-4-(N,N-dialkylamino)-2-butenes (31–53%), 1-(arylsulfonyl)-2-R-2-buten-4-ols (37–61%), and bis[4-(arylsulfonyl)-3-R-but-2-enyl]sulfides (40–70%). The density functional theory B3LYP/6-311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO2Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R2 > 0.97) with the Hammett (σp) constants. 1-Arylsulfonyl 1,3-butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two-centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1-arylsulfonyl 1,3-butadienes are lower than those of 1,3-butadiene explaining their low reactivity towards the Diels–Alder condensation. Copyright © 2015 John Wiley & Sons, Ltd.

ChemInform Abstract: Efficient Method for the Synthesis of Functionalized Basic Maleimides.

A three-step procedure involving Diels–Alder condensation of maleic anhydride with furane, formation of N-substituted imide upon reaction with appropriate diamine, and a final retro Diels–Alder regeneration of the maleic carbon–carbon double bond is proposed for an unequivocal synthesis of N-substituted basic maleimides. The novel method is characterized by mild reaction conditions, easy work-up, high yields, and no need for additional catalysis.

ChemInform Abstract: cis,cis,cis,cis‐1,2,3,4,5‐Pentakis(hydroxymethyl)cyclopentane.

All-cis pentamethanolcyclopentane has been obtained in six steps by Diels–Alder condensation of maleic anhydride with (benzyloxymethyl)cyclopenta-2,4-diene, reduction of the anhydride to a diol that was protected as the acetonide. Then, ozonolysis of the double bond, followed by reduction led to a cis-diol. Then successive deprotections of the three other methanol groups gave the cis,cis,cis,cis-1,2,3,4,5-pentakis(hydroxymethyl)cyclopentane.

Brominating of Oxyphenylimides for Enhancement of Stabilizing Properties of their Derivatives

New bromine-containing oxyphenylimides are synthesized by the Diels–Alder condensation from commercial products. The effect of the bromination of oxyphenylimides on their thermal behavior as comparing with the thermal stability of polystyrene in air is assessed by dynamic thermogravimetric analysis and differential scanning calorimetry. The bromination of oxyphenylimides has different influences on their thermal properties subject to the diene building. The perspectives of the usage of bromine-containing oxyphenylimides for the creation of new polystyrene-stabilizing systems are discussed.

Efficient Method for the Synthesis of Functionalized Basic Maleimides

A three‐step procedure involving Diels–Alder condensation of maleic anhydride with furane, formation of N‐substituted imide upon reaction with appropriate diamine, and a final retro Diels–Alder regeneration of the maleic carbon–carbon double bond is proposed for an unequivocal synthesis of N‐substituted basic maleimides. The novel method is characterized by mild reaction conditions, easy work‐up, high yields, and no need for additional catalysis.

Cis,cis,cis,cis-1,2,3,4,5-Pentakis(hydroxymethyl)cyclopentane

All-cis pentamethanolcyclopentane has been obtained in six steps by Diels–Alder condensation of maleic anhydride with (benzyloxymethyl)cyclopenta-2,4-diene, reduction of the anhydride to a diol that was protected as the acetonide. Then, ozonolysis of the double bond, followed by reduction led to a cis-diol. Then successive deprotections of the three other methanol groups gave the cis,cis,cis,cis-1,2,3,4,5-pentakis(hydroxymethyl)cyclopentane.

Acylation of toluidines with 1,4-dimethylcyclohex-3-enecarbonyl chlorides

Amide group is a component of various compounds, which are of great practical importance. Organic compounds containing the amide groups in the molecule are obtained mainly by the acylation of amines with carboxylic acids and their derivatives. In the literature, there is enough information on the acylation of amines with aromatic carboxylic acids [1], their chlorides [2], esters [3], and anhydrides [4]. Among the acylating agents the carboxylic acid chlorides are the stronger electrophilic reagents. However, there are no published data on the acylation of amines with carboxylic acid chlorides of the cyclohex-3-ene series. We first investigated the acylation of amines with alicyclic carboxylic acid chlorides. Recently, the acylation of aromatic monoand diamines as well as functionally substituted monoamines have been studied [5, 6]. Continuing research in this area, we studied the acylation of toluidine with cyclohex-3-enecarbonyl chloride III. 1,4-Dimethylcyclohexenecarboxylic acid I was synthesized by us via the Diels–Alder condensation of isoprene with methacrylic acid [7]. The isomers separation was performed by the method [8]. DOI: 10.1134/S1070363213010325

Antifungal Activity of Tetrahydroquinolines against Some Phytopathogenic Fungi

Seven synthetic tetrahydroquinolines with different substitution patterns were obtained by an imino Diels-Alder condensation reaction and were evaluated against phytopathogenic fungi. Compounds with a methoxy group showed interesting activity against Cladosporium cladosporoides with a MIC value of 13.75 microg/mL