Alder Cycloaddition Research Articles

Synthesis, characterisation and reactivity studies of chiral β-diketiminate-like supported aluminium Lewis acid complexes towards difficult Diels Alder cycloadditions.

Synthesis and characterisation of several chiral, oxazoline containing β-diketiminate type ligand supported-aluminium compounds are reported. Together with 1 equiv. of Na(BArCl4) (ArCl = 3,5-Cl2-C6H3), these chiral Lewis acid complexes, which possess an "achiral end" and "chiral end" have been successfully utilised as catalysts in asymmetric Diels-Alder reactions of 1,3-cyclohexadiene and several different chalcones. Systematic increase in the steric demand of the ligand's "achiral end" of these complexes resulted in enhanced enantioinduction for the cyclisation of 1,3-cyclohexadiene and chalcone. Further structural modifications of the "chiral end" clearly established that having a tert-butyl group connected to the stereogenic centre of the oxazoline fragment yielded the highest enantioselectivity value for the examined cyclisation. A substrate scope was then expanded using several different dienophiles (i.e. chalcones) generating an enantiomeric excess range of 24-68%.

Improving the performance of ASA in the DAC of 2,5-DMF and ethylene

A variety of methods are employed to synthesize amorphous silica–alumina (ASA) to resolve the role of Al speciation and surface area in the catalytic performance in the Diels–Alder cycloaddition reaction of 2,5-dimethylfuran and ethylene to p-xylene.

Design of Surface-Aligned Main-Chain Liquid-Crystal Networks Prepared under Ambient, Light-Free Conditions Using the Diels-Alder Cycloaddition.

Surface-aligned liquid-crystal networks (LCNs) offer a solution for developing functional materials capable of performing a range of tasks, including actuation, shape memory, and surfaces patterning. Here we show that Diels-Alder cycloaddition can be used to prepare the backbone of planar aligned LCNs under mild ambient conditions without the addition of additives or UV irradiation. The mechanical properties of the networks have robust viscoelastic modulus and stiffness with a reversible local free volume change upon physical aging. This study shows new opportunities to design surface-aligned LCNs based on additive free step-growth Diels-Alder polymerization and enables the potential to incorporate a wider range of photochromic materials into LCNs.

Substituted naphthoxy-phthalonitrile derivatives: Synthesis, substituent effects, DFT, TD-DFT Calculations, antimicrobial properties and DNA interaction studies

Herein, substituted-naphthol derivatives 4a–e were synthesized in two steps, namely the Diels Alder cycloaddition and Cu-catalyzed aromatization reactions, respectively. Then, pththalonitrile derivatives 7–12 have been prepared by a nucleophilic displacement reaction of 3-nitrophthalonitrile with the naphthol derivatives 4a-e, 5 and, obtained in excellent yields. Structural characterization of the compounds was identified by different spectroscopic techniques. Antimicrobial properties of the synthesized compounds were determined by the microdilution procedure against Gram-positive, Gram-negative bacteria, and yeast. Furthermore, the DNA interaction of the compounds were determined by gel electrophoresis. One of the most prominent findings is that compounds 9 and 10 have more inhibitory effects on Gram-positive bacteria than Gram-negative bacteria. These compounds especially exhibited the highest antibacterial potency against S. aureus (625 µg/mL) among Gram-positive bacteria. According to the plasmid DNA interaction results, the synthesized compounds caused changes in the structure and mobility of the plasmid DNA. Then, geometry optimizations and frequency calculations were conducted at B3LYP/6–311 G(d,p) level of DFT, and optimized structures were used for further analyses. The NBO results revealed that the π→π * and n→π * interactions were greatly contributed to lowering the stabilization energy of all compounds (7–12). FMO energy analyses showed that compound 9 has the biggest electrodonating power.

Strain-Induced Regioselective Ring-Opening Cross-Metathesis of Hybrid Cage Propellane Containing both Bicyclo[2.2.1]heptene and Bicyclo[2.2.2]octene Units

AbstractHerein, we report strain-driven regioselective tandem ring-opening cross-metathesis (ROCM) of a linearly fused cage system that contains both bicyclo[2.2.1]heptene and bicyclo[2.2.2]octene units fused to the same cage system. The synthesis of novel cage propellane involves Diels–Alder cycloaddition and [2+2] photocycloaddition as key steps.

Inverse Electron Demand Diels Alder Reaction of Aza-o-Quinone Methides and Enaminones: Accessing 3-Aroyl Quinolines and Indeno[1,2-b]quinolinones.

We have developed a Diels Alder cycloaddition route toward 3-aroyl quinolines from enaminones and in situ generated aza-o-quinone methides. The reaction was found to be general with a range of substituted enaminones and aza-o-quinone methides, and we could validate the applicability of the methodology in gram scale. We also demonstrated a one-pot strategy toward 3-acyl quinolines starting from the corresponding aliphatic ketones. Finally, we utilized the 3-aroyl quinolines for synthesizing indeno[1,2-b]quinolinones via a Pd-catalyzed dual C-H activation approach.

Mechanistic elucidation of Diels–Alder cycloaddition reactions between quinoflavonoid and substituted butadiene using LOL, ELF, QTAIM, and DFT studies

Mechanistic elucidation of Diels–Alder cycloaddition reactions between quinoflavonoid and substituted butadiene using LOL, ELF, QTAIM, and DFT studies

Theoretical Study on the Diels–Alder Reaction of Fullerenes: Analysis of Isomerism, Aromaticity, and Solvation

Fullerenes are reactive as dienophiles in Diels–Alder reactions. Their distinctive molecular shape and properties result in interesting and sometimes elusive reaction patterns. Herein, to contribute to the understanding of fullerene reactivity, we evaluate the energies of reactions for Diels–Alder cycloadditions of C60, C70, and IC60MA with anthracene (Ant), by means of DFT computational analysis in vacuum and solution. The methods used showed little differentiation between the reactivity of the different fullerenes. The C70-Ant adducts where addition takes place near the edge of the fullerene were found to be the most stable regioisomers. For the IC60MA-Ant adducts, the calculated energies of reaction increase in the order: equatorial > trans-3 > trans-2 ≈ trans-4 ≈ trans-1 > cis-3 > cis-2. The change in the functional suggests the existence of stabilizing dispersive interactions between the surface of the fullerene and the addends. HOMA (harmonic oscillator model of aromaticity) analysis indicated an increase in aromaticity in the fullerene hexagons adjacent to the bonded addend. This increase is bigger in the rings of bisadduct isomers that are simultaneously adjacent to both addends, which helps explain the extra stability of the equatorial isomers. Solvation by m-xylene decreases the exothermicity of the reactions studied but has little distinguishing effect on the possible isomers. Thermal corrections reduce the exothermicity of the reactions by ~10 kJ∙mol−1.

Cyclotriphophazene-Centered Six-Arm Eugenol-Linked Low-Dielectric Materials with High Thermostability and Transparency

Two silicon-containing eugenol-based benzocyclobutene monomers were prepared by a simple solvent-free hydrosilylation reaction. After heat treatment, a series of materials were obtained by a free radical addition reaction, [4 + 4] cycloaddition, or [4 + 2] Diels–Alder cycloaddition. All polymers displayed high thermostability with a 5% weight loss temperature (T5d) of over 410 °C and a glass transition temperature (Tg) of up to 216 °C as well as a good transmittance of 90% varying from 500 to 800 nm. In particular, all polymers also exhibited good hydrophobicity with contact angles exceeding 100° and water absorption as low as 8‰ after immersing in boiling water for 72 h. It should be noted that P3 showed excellent dielectric properties with a dielectric constant (Dk) of 2.48 and a dielectric loss (Df) of 6.38 × 10–3 at a high frequency of 2 GHz as well as good flame retardancy due to the high content of cyclotriphophazene compared with those of P1, P2, and previously reported biobased materials. The above advantages indicate that eugenol-based low-dielectric materials have great potential for application in encapsulation resins in the field of microelectronics.

Diastereo- and Enantioselective Inverse-Electron-Demand Diels-Alder Cycloaddition between 2-Pyrones and Acyclic Enol Ethers.

A broadly applicable diastereo- and enantioselective inverse-electron-demand Diels-Alder reaction of 2-pyrones and acyclic enol ethers is reported herein. Using a copper(II)-BOX catalytic system, bridged bicyclic lactones are obtained in very high yields (up to 99 % yield) and enantioselectivities (up to 99 % ee) from diversely substituted 2-pyrones and acyclic enol ethers. Mechanistic experiments as well as DFT calculations indicate the occurrence of a stepwise mechanism. The synthetic potential of the bridged bicyclic lactones is showcased by the enantioselective synthesis of polyfunctional cyclohexenes and cyclohexadienes, as well as a carbasugar unit.

Diastereo‐ and Enantioselective Inverse‐Electron‐Demand Diels–Alder Cycloaddition between 2‐Pyrones and Acyclic Enol Ethers

A broadly applicable diastereo- and enantioselective inverse-electron-demand Diels–Alder reaction of 2-pyrones and acyclic enol ethers is reported herein. Using a copper(II)-BOX catalytic system, bridged bicyclic lactones are obtained in very high yields (up to 99 % yield) and enantioselectivities (up to 99 % ee) from diversely substituted 2-pyrones and acyclic enol ethers. Mechanistic experiments as well as DFT calculations indicate the occurrence of a stepwise mechanism. The synthetic potential of the bridged bicyclic lactones is showcased by the enantioselective synthesis of polyfunctional cyclohexenes and cyclohexadienes, as well as a carbasugar unit.

Tert-Butyl(2-oxo-2H-pyran-5-yl)carbamate as the First Chameleon Diene Bearing an Electron-Donating Substituent.

The 2(H)-pyran-2-one bearing electron-donating tert-butylcarbamate (BocNH-) group at the 5- position is a “chameleon” diene and undergoes efficient Diels–Alder cycloadditions with alkene dienophiles with both electron-rich and electron-deficient substituents. Cycloadditions afford the 5-substituted bicyclic lactone cycloadducts regardless of the electronic nature of the dienophile. However, cycloadditions with electronically matched electron-deficient dienophiles proceed faster than those with electronically mismatched electron-rich dienophiles.

Total Synthesis of (+)‐Alstonlarsine A

An enantioselective total synthesis of (+)-alstonlarsine A (1), a monoterpenoid indole alkaloid possessing a unique pentacyclic skeleton as well as a rare biological activity, is achieved. The key step is an efficient domino sequence, comprising enamine formation followed by an inverse-electron-demand intramolecular dearomative Diels–Alder cycloaddition for the construction of 9-azatricyclo[4.3.1.03,8]decane core. The key intermediate for this domino sequence was synthesized by a newly developed methodology, relying on indole C(2)-H bond functionalization, combined with intramolecular Horner–Wadsworth–Emmons reaction. This tactical combination offers a new general entry into other (privileged) tricyclic frameworks possessing indole ring fused to 6-, 7- or 8-membered rings.

Enantioselective oxa‐Diels–Alder Sequences of Dendralenes

Diene-transmissive hetero-Diels–Alder sequences involving carbonyl dienophiles are reported for the first time. High enantioselectivities are achieved in the reaction of phenylglyoxal with a broad range of dendralene structures, through the optimization of a Pd2+ catalyst system. The initial catalyst-controlled enantioselective oxa-Diels–Alder (ODA) cycloaddition to a [3]dendralene generates a dihydropyran carrying a semicyclic diene. This participates in a subsequent catalyst or substrate-controlled Diels–Alder reaction to generate sp3-rich fused polycyclic systems containing both heterocycles and carbocycles. Computational investigations reveal a concerted asynchronous mechanism. π-Complexation of a diene C=C bond to Pd2+ occurs in both the pre-transition state (TS) complex and in cycloaddition TSs, controlling stereoselectivity. A formal enantioselective [4+2]cycloaddition of a CO2 dienophile is demonstrated.

Influence of Tetraphenylbenzene on the OFET Behavior of Triarylamines

AbstractA series of new tetraphenylbenzene‐based triarylamines are successfully synthesized by employing the Diels–Alder cycloaddition reaction. The molecules exhibited good solubility in common organic solvents and thermal stability up to 500 °C. Molecular geometry and charge distribution of the molecules are envisioned by density functional theory. The high‐lying highest occupied molecular orbital (HOMO) level (‐5 eV) of compounds enables the p‐channel conductivity. The influence of tetraphenylbenzene units on charge‐delocalization of HOMO, crystalline packing, and organic field‐effect transistor (OFET) characteristics is analyzed. OFETs are fabricated under ambient conditions by solution‐processable method, and the devices displayed promising performance with charge carrier mobility µh up to 0.72 cm2 V−1 s−1, on/off ratio of 107, and lowest VT of −2 V.

Total Synthesis of Ophiorrhine A, G and Ophiorrhiside E Featuring a Bioinspired Intramolecular Diels–Alder Cycloaddition**

AbstractWe report the first total synthesis of the monoterpene indole alkaloids ophiorrhine A via a late stage bioinspired intramolecular Diels–Alder cycloaddition to form the intricate bridged and spirannic polycyclic system. Several strategies were investigated to construct the indolopyridone moiety of ophiorrhiside E, the postulated biosynthetic precursor of ophiorrhine A. Eventually, the Friedel–Crafts‐type coupling of N‐methyl indolyl‐acetamide with a secologanin‐derived acid chloride delivered ophiorrhine G. Cyclodehydration of a protected form of the latter was followed by the desired spontaneous intramolecular Diels–Alder cycloaddition of protected ophiorrhiside E leading to ophiorrhine A.

Crosslinking starch with Diels–Alder reaction: water‐soluble materials and water‐mediated processes

AbstractThe click Diels–Alder cycloaddition is a one‐step high‐yield reaction that does not require catalysts, does not generate side products and can be performed at mild conditions in an aqueous medium, representing a good method for biomaterials coupling and synthesis. It exploits functional groups that can be grafted onto natural polymers or other molecules and can be used for the preparation of biomaterials such as biocompatible hydrogels, a nascent field of application of the Diels–Alder reaction. If performed in an aqueous medium, at biological pH and body temperature, it can be used in internal body systems for drug and cell release. Here we report the grafting of the furan ring from furfuryl alcohol to chemically oxidized starch and its crosslinking via the Diels–Alder reaction, in aqueous medium, at 37 °C, mimicking the body conditions in vitro. Since the functional groups used in this chemical strategy are sparingly studied for such applications, and their behavior is not described in the literature, the biocompatibility of the crosslinked starch as well as that of the precursor reagents were evaluated by cytotoxicity tests using GM07492 human cells. The results reveal that the furan‐crosslinked starch is a promising candidate for cell encapsulation and delivery within the body. © 2022 Society of Industrial Chemistry.

Bridgehead Alkene-Enabled Strain-Driven Bioorthogonal Reaction.

Herein, we report a novel bioorthogonal reaction that hinges on a bridgehead alkene (BHA)-enabled inverse-electron-demand Diels-Alder (IEDDA) cycloaddition. Readily accessible from natural product β-caryophyllene, the strained BHA displays high reactivity toward the IEDDA reaction while maintaining excellent biocompatibility. The developed IEDDA reaction has been applied to in vitro protein labeling and pretargeted live cell imaging.

Stereoselective cycloaddition of biologically active thioindoline with the smallest nanocage in gas phase versus solution via density functional theory

AbstractA fine speculation of enantioselectivity prior to the expensive experimental endeavors is truly one of the ultimate goals of the computational organic chemists. In this survey, we have predicted stereo specificity for hetero Diels–Alder (DA) cycloaddition of (E)‐3‐benzylidene‐indoline‐2‐thione (I) with C20 to give (Ia) as drug delivery in the gas phase and in solution, at density functional theory (DFT)–self‐consistent reaction field (SCRF). The enthalpy difference between liquid (l) and gas (g) phases (∆Hl‐g), as well as activation energy (Eexo≠, Eendo≠) of Ia cycloadduct, appears proportional to the dielectric constant of solvent (ε). In contrast to the above trends, kinetic stability based on ∆EL‐H of Ia, develops in opposite to that of ε. The more stability of Ia is attributed to its H―bonding, and dipole–dipole interaction in water. The energy barrier of exo transition states (TS) is low; hence, cycloaddition is recommended to be of synthetically interest for preparation of asymmetric nano compound. Moreover, the π‐π aromatic stacking among the substituted phenyl ring and C20 (πsubstituted phenyl ring ↔ πC20) has significant effect on destabilization of endo TS. This DA reaction have polar nature according to one‐step mechanism, that comprises an initial hetero‐DA reaction yielding Ia, which experiences a subsequent [3,3] sigmatropic shift to yield the expected formal cycloadduct. This is a consequence of more polar nature of reaction, due to lower nucleophilicity (N), higher electrophilicity (ω), higher maximum electronic charge (ΔNmax), more polarity (μ), and more global electron density transfer (GEDT) of Ia in polar solvents (especially in water) in comparison to gas phase. This polar character is given by the electrophilic character of the C20 dienophile (ω = 5.29 eV) and nucleophilic character of the 1,3‐diene molecule (I) (N = 3.70 eV). Additionally, molecular mechanism of the considered reaction is substantially different from the DA reactions between simple 1,3‐diene and dienophiles.

Solvent effect on cycloaddition of C20 nanofullerene with indoline‐2‐one, at density functional theory

AbstractThe biologically active (E)‐3‐(furan‐2‐yl)methylene‐indoline‐2‐one (I) is studied, in the gas phase, C6H6, C2H4Cl2, EtOH, MeNO2, DMSO, and H2O using the self‐consistent reaction field (SCRF)—density functional theory (DFT). This species has been used in tumor growth, metastasis, and angiogenesis. A mainly interesting issue is the solvent effect on the stability, geometry, and energy of intermolecular hetero‐Diels–Alder cycloaddition of I with C20 to yield drug delivery (Ia). By optimization of adduct (Ia) from gas phase to nonpolar and then polar solvent, the following results is obtained: (1) The trend of thermodynamic and kinetic stability and also polarity seem proportional to the dielectric constant of the used solvent and formation of the hydrogen bonding. (2) In contrast to general belief that the endo isomer appears more stable than exo isomer, here, the exo isomer appears more stable than endo isomer. (3) The exo cycloaddition can be carried out thermally at room temperature and currently hold responsible for regioselectivity. (4) The possibility of endo cycloaddition is favorable by the lowest energy barrier of 4.2 kcal/mol probed in benzene, while the highest energy barrier of 7.3 kcal/mol is estimated in water. (5) Nonbonding electrostatic interaction between the sulfur heteroatom and nanocage, as well as the π–π aromatic stacking, appears to have significant destabilizing effect on the endo isomer. (6) In going from exo transition state (TS) and endo TS to and Ia cycloadduct, the molecular electrostatic potential is changed as a function of shape, size, symmetry, and regioselectivity.