Diene Structure Research Articles

Introducing Diels‐Alder reaction with carbon nanotubes for the enhanced repair performance of epoxy resin modified asphalt

AbstractEpoxy asphalt, a thermosetting polymer, is characterized by stable, irreversible internal chemical bonds that prevent recovery and spontaneous micro‐crack healing, unlike conventional asphalt. This study introduces a renewable nano‐modifier synthesized via esterification of carboxyl‐functionalized carbon nanotubes (CNTs‐COOH) and furfuryl alcohol (FA), termed CNTs‐FA. The successful synthesis of CNTs‐FA was confirmed through various microscopic techniques. Integrating CNTs‐FA into epoxy asphalt materials, the optimal dosage was identified as 0.05% of the total epoxy asphalt mass using tensile tests and fluorescence microscopy. Thermal reversible effects and mechanisms were further analyzed through multiple regeneration cycles using tensile properties, fluorescence microscopy, and infrared spectroscopy. The study elucidates that the thermal reversibility in epoxy asphalt is facilitated by the Diels‐Alder (DA) reaction between the conjugated diene structure in FA and the curing agent oleylamine. This research provides an effective solution to the non‐recoverability and unrepairable micro‐cracks of traditional epoxy asphalt mixtures.Highlights CNTs‐FA was successfully prepared by esterification reaction. Using nano modification methods, introduce DA reaction into curing system. Renewable function of epoxy asphalt by DA reversible reaction.

Diene Salts of the Adamantane Series: Synthesis, Structure, and Chemical Transformations

AbstractMono‐ and bis‐pyridinium, phosphonium and sulfonium allylic salts, containing adamantane fragment, have been obtained from the substitution reaction in 1,4‐dibromo‐2‐butene. It was found, that the attack of triethylamine undergoes from the sterically less hindered side, leading to deprotonation and subsequent elimination of the molecular fragment with the formation of a new salt of diene structure. Quantum chemical calculations were used to confirm the structure of one of the products by correlation analysis of experimental and calculated NMR data that confirmed the s‐cisoid conformation of the diene. It was found, that obtained dienes may be used as substrates in Diels‐Alder reaction despite their high sterical hinderance.

Distortion Rules: Diene Ring Size Effects in Diels‐Alder Reactions with Triazolinediones

AbstractTriazolinediones (TADs) are highly reactive electrophiles used in several processes within the field of organic chemistry, especially in Diels‐Alder cycloadditions. The reactions of TADs with cyclic dienes have been observed to depend on the diene structure and size. To investigate the role of diene structure in the reactivity of TADs, computational chemistry based on DFT and Activation Strain Model were employed to quantitatively assess the impact of distortion and interaction energies on the observed reactivity. Calculations suggest that the reactions are endo selective based on lower energy barriers compared to the exo pathway. Additionally, the trends in reactivity agree with experimental observations: cyclopentadiene is the more reactive diene, followed by cyclohexadiene and cycloheptadiene. The ASM analysis reveals that this trend is a consequence of the degree of distortion the reactants along the reaction coordinate. These distortion energies also allowed to explain why the endo selective route is preferred over the exo one.

Merging Styrene and Diene Structures to a Cyclic Diene: Anionic Polymerization of 1-Vinylcyclohexene (VCH).

We report the first anionic polymerization of 1-vinylcyclohexene (VCH). This structure may be considered as an intermediate between dienes and styrene. The polymerization of this cyclic 1,2-disubstituted 1,3-diene proceeded quantitatively in cyclohexane at 25 °C with sec-butyllithium as an initiator. The obtained polymers have well-controlled molecular weights in the range of 5 to 142 kg mol-1 , controlled by the molar ratio of monomer and initiator, with narrow molecular weight distributions (Đ<1.07-1.20). In situ 1 H NMR kinetic characterization revealed a weak gradient structure for the copolymers of styrene and VCH, (rSty =2.55, rVCH =0.39). P(VCH) obtained in cyclohexane with sec-BuLi as an initiator showed both 1,4- and 3,4-incorporation mode (ratio: 64 : 36). It was demonstrated that the microstructure of the resulting P(VCH) can be altered by the addition of a modifier (THF), resulting in increasing 3,4-microstructure (up to 78 %) and elevated glass-transition temperature up to 89 °C. Thus, the monomer VCH polymerizes carbanionically like a diene, however leading to rigid polymers with high glass transition temperature, which provides interesting options for combination with other dienes to well-defined polymer architectures and materials.

High linoleic waste sunflower oil: A distinctive recycled source of self-healing agent for smart metal coatings

High Linoleic Waste Sunflower Oil (HLWSO) is a new self-healing agent viable to be encapsulated. Meanwhile, the unique mechanism behind the synthesis of microcapsules is deeply illustrated; the emulsification process of HLWSO by anionic surfactant and microencapsulation of HLWSO. In addition, the application of microencapsulated HLWSO in the coating matrix by the layering method is presented followed by a detailed explanation of the self-healing mechanism of a smart coating incorporating the polymerization mechanism of HLWSO developed by the diene structure. Microencapsulation of high linoleic waste sunflower oil (HLWSO) is a wall formation process in which urea-formaldehyde (UF) is attached with emulsified HLWSO to form a microcapsule. In this study, the HLWSO from recycled cooking oil is uniquely bonded with a diene structure, thus possessing the ability to dry fast and be encapsulated via the in-situ polymerization method. The microencapsulated HLWSO was characterized using Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transformation Infra-Red Spectroscopy (FTIR). The optimum microcapsules synthesized from HLWSO resulted in a smooth shell structure with 2.88 μm diameter microcapsules at 0.31 μm shell thickness and 66% core content. It was demonstrated that increased stirring speed decreases the size, shell thickness, and core content of the microcapsules. The FTIR results indicated that HLWSO as a core, while urea-formaldehyde acted as a shell of microcapsules. The scratch on the coating matrix embedded with HLWSO was healed after five days. The corrosion rate of optimum sample was 0.0574 mm/year, with an optimum reduction of 58% from the reference sample. This study revealed that the HLWSO from recycled sources is a viable self-healing agent to be microencapsulated. The smart coating embedded with HLWSO also displayed self-healing performance, reduced corrosion rate and beneficial for the advancement of corrosion control technology.

Ligand-Enabled Sequential C(sp3)-H and C(sp2)-H Diolefination Reaction via Palladium Catalyst.

Palladium-catalyzed sequential C(sp3)-H and C(sp2)-H bond diolefination reaction of o-toluidine has been realized for the first time using acetyl-protected aminoethyl phenyl thioether ligands. This novel reaction allows for preparation of the conjugated diene structure via an immediate second olefination on the basis of the first C(sp3)-H olefination in one pot. Various triflyl-protected anilines and acrylates were used as coupling partners elegantly. Furthermore, the unpurified diolefination products can be easily converted to tetrahydroquinoline derivatives.

Progress toward Polymerization Reaction Monitoring with Different Dienes: How Small Amounts of Dienes Affect ansa-Zirconocenes/Borate/Triisobutylaluminium Catalyst Systems.

The objectives of this work were to address the fundamental characteristics of ansa-zirconocene catalyzed E/diene copolymerization and E/diene/1-hexene and E/diene/propylene terpolymerizations, and the quantitative relationship between diene structure and polymer chain propagation rate constant in term of quantifiable catalytic active sites. One of the most important but unknown factors in olefins ansa-zirconocene complexes is the distribution of the catalyst between sites actively participating in polymer chain formation and dormant sites. A set of ethylene/dienes copolymerizations, and ethylene/dienes/1-hexene and ethylene/dienes/1-hexene terpolymerizations catalyzed with ansa-zirconocenes/borate/triisobutylaluminium (rac-Et(Ind)2ZrCl2/[Ph3C][B(C6F5)4]/triisobutylaluminium (TIBA) were performed in toluene at 50 °C To determine the active center [C*]/[Zr] ratio variation in the copolymerization of E with different dienes and their terpolymerization with 1-hexene and propylene, each polymer propagation chain ends were quenched with 2-thiophenecarbonyl, which selectively quenches the metal–polymer bonds through acyl chloride. The ethylene, propylene, 1-hexene, and diene composition-based propagation rate constants (kpE, kpP, kp1-H, and kpdiene), thermal (melting and crystalline) properties, composition (mol% of ethylene, propylene, 1-hexene, and diene), molecular weight, and polydispersity were also studied in this work. Systematic comparisons of the proportion of catalytically [Zr]/[C*] active sites and polymerization rate constant (kp) for ansa-zirconocenes catalyzed E/diene, E/diene/1-hexene, and E/diene/propylene polymerization have not been reported before. We evaluated the addition of 1-hexene and propylene as termonomers in the copolymerization with E/diene. To make a comparison for each diene under identical conditions, we started the polymerization by introducing an 80/20 mole ratio of E/P and 0.12 mol/L of 1-hexene in the system. The catalyst behavior against different dienes, 1-hexene, and propylene is very interesting, including changes in thermal properties, cyclization of 1-hexene, and decreased incorporation of isoprene and butadiene, changes in the diffusion barriers in the system, and its effect on kp.

Synthesis of a Bicyclo[2.2.1]heptane Skeleton with Two Oxy-Functionalized Bridgehead Carbons via the Diels-Alder Reaction.

We describe a synthetic method for a bicyclo[2.2.1]heptane skeleton with two oxy-functionalized bridgehead carbons. This method involves an intermolecular Diels-Alder reaction using 5,5-disubstituted 1,4-bis(silyloxy)-1,3-cyclopentadienes, the diene structure of which has never been synthesized. Furthermore, the intramolecular Diels-Alder reaction using a diene bearing a dienophile moiety at the C-5 position can provide a tricyclic carbon framework that includes the bicyclo[2.2.1]heptane skeleton. The novel bicyclo[2.2.1]heptane derivatives could be utilized as versatile building blocks for organic synthetic chemistry.

Pentacyclic Cytochalasins and Their Derivatives from the Endophytic Fungus Phomopsis sp. xz-18

Eight new cytochalasins 1–8 and ten known analogs 9–18 were isolated from the endophytic fungus Phomopsis sp. xz-18. The planar structures of the cytochalasins were determined by HR-ESI-MS and NMR analysis. Compounds 1, 2, 9 and 10 were 5/6/6/7/5-fused pentacyclic cytochalasins; compounds 3 and 4 had conjugated diene structures in the macrocycle; and compound 6 had a β,γ-unsaturated ketone. The absolute configuration of 6 was confirmed for the first time by the octant rule. The acid-free purification process proved that the pentacyclic system was a natural biosynthetic product and not an acid-mediated intramolecular cyclized artifact. The new compounds did not exhibit activities against human cancer cell lines in cytotoxicity bioassays or antipathogenic fungal activity, but compounds 1, 3 and 4 showed moderate antibacterial activity in disk diffusion assays.

Allylic Hydroxylation Activity Is a Source of Saponin Chemodiversity in the Genus Glycyrrhiza.

Licorice (Glycyrrhiza) produces glycyrrhizin, a valuable triterpenoid saponin, which exhibits persistent sweetness and broad pharmacological activities. In the genus Glycyrrhiza, three species, Glycyrrhiza uralensis, Glycyrrhiza glabra and Glycyrrhiza inflata, produce glycyrrhizin as their main triterpenoid saponin, which has a ketone group at C-11. Other Glycyrrhiza species produce mainly oleanane-type saponins, which harbor homoannular or heteroannular diene structures that lack the C-11 ketone. Although the glycyrrhizin biosynthetic pathway has been fully elucidated, the pathway involving saponins with diene structures remains unclear. CYP88D6 from G. uralensis is a key enzyme in glycyrrhizin biosynthesis, catalyzing the sequential two-step oxidation of β-amyrin at position C-11 to produce 11-oxo-β-amyrin. In this study, we evaluated the functions of CYP88D6 homologs from the glycyrrhizin-producing species G. glabra and G. inflata and from the non-glycyrrhizin-producing species Glycyrrhiza pallidiflora and Glycyrrhiza macedonica, using yeast engineered to supply β-amyrin as a substrate. Yeast expressing CYP88D6 homologs from glycyrrhizin-producing species produced 11-oxo-β-amyrin. However, yeast expressing CYP88D6 homologs (such as CYP88D15) from the non-glycyrrhizin-producing Glycyrrhiza species accumulated oleana-9(11),12-dien-3β-ol and oleana-11,13(18)-dien-3β-ol; these diene compounds are non-enzymatic or yeast endogenous enzymatic dehydration derivatives of 11α-hydroxy-β-amyrin, a direct reaction product of CYP88D15. These results suggest that the activities of CYP88D6 homologs, particularly their ability to catalyze the second oxidation, could influence glycyrrhizin productivity and diversify the chemical structures of saponins in Glycyrrhiza plants. A synthetic biological approach to engineer CYP88D15 could enable the production of pharmacologically active saponins with diene structures, such as saikosaponins, whose biosynthetic pathways have yet to be fully characterized.

Increase of oxidation rate of uric acid by singlet oxygen at higher pH.

Singlet oxygen prefers to react with an electron-rich double bonds. We observed that the oxidation rate for uric acid with singlet oxygen increased with increasing pH and the oxidation rate dramatically was elevated at around pH 5.4 and 9.8, which are the acidity constants of uric acid, pKa1 and pKa2, respectively. Furthermore, we observed that the absorbance near 200 nm and the molar extinction coefficient (ɛ) increased with increasing pH, similar to the change in oxidation rate. Computer calculations by Chong [Chong, J Theor Comput Sci 2013; 1(1)] revealed that uric acid elongates its C=N conjugated diene structure with increasing pH. This is correlated with an increase in the UV absorbance of C=C double bonds near 200 nm, and may indicate higher electron density in the double bonds. Therefore, we concluded that the increased oxidation rate is due to elongation of the C=N conjugated polyene system at higher pH. On the other hand, the major products were 4-hydroxyallantoin and parabanic acid (hydrolyzed to oxaluric acid at pH 10.7), suggesting that the reaction pathways were the same regardless of pH. Finally, possible reaction schemes are presented.

Catalytic Synthesis of Optically Active Polycyclic Heterocyclic Compounds

In basic pharmaceutical sciences to achieve drug development, research on the efficient chemical synthesis of small molecules having cyclic skeletons is important. We have been engaged in the development of artificial catalysts for asymmetric ring formation reactions that exclusively synthesize right-handed or left-handed cyclic compounds and have achieved the construction of optically active cyclic skeletons using our original catalysts. The synthesis of biologically active compounds was facilitated through six-membered ring construction by Diels-Alder reaction of Danishefsky diene; however, no asymmetric variant of the reaction has been achieved. We approached this unresolved issue using multi-coordinated lanthanide metals. A new chiral lanthanide catalyst was developed, and the catalytic asymmetric Diels-Alder reaction of Danishefsky diene was realized for the first time. By modifying the chemical structure of Danishefsky diene, we applied the lanthanide catalyst to the syntheses of polycyclic compounds and biologically active compounds. We achieved the asymmetric synthesis of natural products, antibacterial and antimalarial compounds, and an anti-obesity drug lead compound. Moreover, the novel catalyst exhibited higher performance than the previously reported ones. The latest generation of the catalyst can be handled stably in air at room temperature. Furthermore, we succeeded in the development of new catalysts by focusing on the properties of its metal precursors, such as nickel and indium, and achieved the construction of polycyclic skeletons by using these catalysts.

Effect of segment structure on the thermal stability ofCPVCin theGas–Solid PVCchlorination process

AbstractThe chlorination of the polyvinyl chloride resin with different ratios of CH2, CHCl2, and CCl2was carried out through a gas–solid process by varying the temperature, reaction time, and chlorine concentration. The rheological properties and thermal stability of the resin were characterized.13C NMR was used to characterize the segment structure of the resin. In addition, conjugated diene structure was determined by UV–Visible to study its chlorination process. The results show that CCl2 units in the structure promote the dehydrochlorination of CPVC, forming a conjugated diene structure and reducing the rheological properties and thermal stability. In contrast, the formation of CHCl in the chlorination process increased the thermal stability of the resin. Moreover, a structure‐effect relationship between the structure and performance has been established, and a stepwise process of chlorination was obtained by analyzing the changes of the structure segment content at different stages.

Catalytic Functionalization of 1,3-Butadiene by Carbon Electrophiles

1,3-Butadiene is a useful C4 carbon source for the production of basic chemicals; but use as carbon feedstock often presents regioselectivity problems arising from its conjugated diene structure. This review summarizes the functionalization of 1,3-butadiene with carbon electrophiles by using homogeneous transition metal catalysts. A copper catalyst generated by treatment of Cu salt with alkyl Grignard reagent catalyzed internal carbon selective reductive alkylation of 1,3-butadiene with alkyl fluoride as a carbon electrophile and the alkyl Grignard reagent as a hydride source. In contrast, nickel promoted dimerization and alkylarylation of 1,3-butadiene with a similar combination of substrates. Using polyfluoroarenes as the carbon electrophiles, similar transformations proceeded to achieve the functionalization of 1,3-butadiene. The substrate scope as well as details of the reaction mechanism of these transformations are discussed.

Enantioselective Stereodivergent Approach to α-Hydroxy Skipped Dienes: Synthesis of the Western Polyene Fragment of Corallopyronin A

Synthesis of the western polyene fragment of corallopyronin A is documented. The α-hydroxy skipped diene structure is stereoselectively synthesized by our method consisting of enantioselective allenylation of an aldehyde, hydroboration of the resulting 1,1-disubstituted allene and Migita-Kosugi-Stille coupling. The developed approach could become a general platform for α-hydroxy skipped dienes embedded in a number of biologically active natural products because all eight stereoisomers of the α-hydroxy skipped diene are potentially available from the same aldehyde through these three stereodivergent reactions.

Potassium Salts of 2,5-Bis(trimethylsilyl)-Germolide: Switching between Aromatic and Non-Aromatic States.

The reduction of a 1-mesityl-2,5-bis-trimethylsilylchlorogermole 8 with KC8 is reported. While the reaction with one equivalent of KC8 gave the dimer with a Ge-Ge bond 10, excess of KC8 (four equivalents) resulted in the formation of the potassium salt of the germole dianion, 11 with reductive cleavage of the Ge-C bond. Careful reduction with two equivalents of KC8 in THF provided the potassium salt of the planar germolide 5. Its solid-state structure revealed contact ion pairs with the potassium ion η5 -coordinated to the germacyclopentadienide ring. The molecular structure of the anion indicates a high degree of cyclic electron delocalization, in agreement with results from DFT calculations. Separation of the ion pair by complexation of the potassium ions with 18-crown-6 triggers the isomerization to germolide 6, which is characterized by a pyramidal coordination sphere of the germanium atom and a localized diene structure. The isomers 5 and 6 represent a rare example for a structurally manifested switch between a non-aromatic and an aromatic state induced by an external stimulus, in this case the complexation of the counter cation.

The influence of two‐stage variable temperature suspension polymerization on polyvinyl chloride resin: The molecular chain segment structure and thermal stability

The suspension polymerization of polyvinyl chloride (PVC) was carried out at two different constant temperature conditions (52.5°C and 57.5°C) and at two‐stage variable temperature conditions (52.5–57.5°C). The molecular weight and molecular weight distribution were characterized by gel permeation chromatography (GPC). The unstable chlorine content, total double bond content, and conjugated diene content were explored via phenol substitution, catalytic bromine addition, and ultraviolet–visible spectroscopy (UV–Vis). pH meter and thermogravimetric analyzer (TGA) were used for the determination of the thermal stability. According to the results, due to the gradual consumption of the impurities and the effect of the local high temperature in the early stage of polymerization, which caused more molecular chain‐transfer and more structural defects, a large number of oligomers generated. A rapid increase in the molecular weight could be found until the conversion was close to 23%. A lower temperature should be conducive to reducing the structural defects in molecular segments. Based on these observations, we applied two‐stage variable temperature polymerization and compared the PVC resin at a similar molecular weight at a constant temperature of 56°C. The PVC resin produced by the two‐stage variable temperature polymerization process obtained a similar Polydispersity index (PDI), reduced the unstable chlorine content by 15.11%, reduced the total double bond structure content by 8.81%, reduced the conjugated diene structure content by 13.86%, and increased the thermal stability time by 13.91%, thereby improving the thermal stability of the PVC resin. J. VINYL ADDIT. TECHNOL., 25:E80–E87, 2019. © 2018 Society of Plastics Engineers

Influence of γ-Irradiation on the Optical Properties of the Polyimide–YBa2Cu3O6.7 System

Influence of γ-irradiation on the optical properties of a polyimide film and its polymer compositions with fillers of a dispersed powder of a high-temperature superconductor ҮBa2Cu3O6.7 (YBaCuO) with concentrations of 0.05, 0.10, and 0.50 wt.% was studied. It was established that γ-irradiation with a dose up to 600 kGy does not affect the transparency of polyimide films in the visible region of the spectrum. However, at irradiation doses of 250 and 600 kGy, a weakly expressed fine structure appears in the spectra of polyimide films in the range of 220–300 nm due to the contribution of the resulting diene structures to the optical transmission and the increased content of oxygen atoms. The YBaCuO filler and γ-irradiation cause the polyimide transition from the amorphous state to the crystalline state, which is manifested in a sharp change in the spectrum in the range of ~2.3–3.9 eV. A significant increase in the extinction coefficient was found in the composite containing 0.50 wt.% of the filler that is associated with an increase in the radius of action of structurally active fillers on the macromolecules of the matrix.

Synthesis of Non-Conjugated Trienes via In Situ Hydrovinylation/Wittig Olefination of Unsaturated Phosphonium Salts

A cobalt-catalysed 1,4-hydrovinylation reaction is successfully applied in a sequential three-component transformation of unsaturated phosphonium bromides, 1,3-dienes, and aldehydes leading to non-conjugated products with a 1,4-diene subunit in good to excellent yields. The hydrovinylation provides regioselectively diene structures with one exo double bond whereas the third double bond can be introduced via an in situ Wittig or Horner–Wadsworth–Emmons olefination leading to 1,4,7-trienes suitable for further double bond functionalisations.

Macrolide Synthesis through Intramolecular Oxidative Cross-Coupling of Alkenes.

A RhIII -catalyzed intramolecular oxidative cross-coupling between double bonds for the synthesis of macrolides is described. Under the optimized reaction conditions, macrocycles containing a diene moiety can be formed in reasonable yields and with excellent chemo- and stereoselectivity. This method provides an efficient approach to synthesize macrocyclic compounds containing a 1,3-conjugated diene structure.