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Journal articles on the topic 'Diels-Alder Reaction'

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Author: Grafiati

Published: 4 June 2021

Last updated: 1 August 2024

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1

Sun, Simin, Chong Teng, and Jiaxi Xu. "Microwave Thermal Effect on Diels-Alder Reaction of Furan and Maleimide." Current Microwave Chemistry 7, no. 1 (June 23, 2020): 67–73. http://dx.doi.org/10.2174/2213335607666200101093318.

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Background: Higher temperature regions (hot spots) have been observed in organic reactions and are attributed to microwave selective heating. The accumulated heat in reaction systems accelerates certain reactions. Methods: The theoretical calculation was applied to select a suitable Diels-Alder reaction as a molecular probe to determine the microwave thermal effect on Diels-Alder reaction, one class of bimolecular reactions. The kinetic investigations were utilized to determine the reaction activation energies and further to calculate the actual reaction temperatures under different microwave conditions from the Arrhenius equation. Results: On the basis of the theoretical calculational results, Diels-Alder reaction of furan and maleimide was selected as a molecular probe to determine the microwave thermal effect in Diels- Alder reaction. Their activation energies under thermal conditions were determined from kinetic data by using the Arrhenius equation. The actual reaction temperatures under different microwave conditions were further deduced from their activation energies and the Arrhenius equation. Conclusion: Higher temperature regions (hot spots) were observed in Diels-Alder reaction, and they are more obvious in less polar solvents than those in more polar solvents in the microwave irradiated reactions.

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2

Li, Na, Xianrui Liang, and Weike Su. "New insights into the asymmetric Diels–Alder reaction: the endo- and S-selective retro-Diels–Alder reaction." RSC Advances 5, no. 128 (2015): 106234–38. http://dx.doi.org/10.1039/c5ra17788j.

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3

Cain, David, Calum McLaughlin, John Molloy, Cameron Carpenter-Warren, Niall Anderson, and Allan Watson. "A Cascade Suzuki–Miyaura/Diels–Alder Protocol: Exploring the Bifunctional Utility of Vinyl Bpin." Synlett 30, no. 07 (October 24, 2018): 787–91. http://dx.doi.org/10.1055/s-0037-1611228.

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Cascade reactions are an important strategy in reaction design, allowing streamlining of chemical synthesis. Here we report a cascade Suzuki–Miyaura/Diels–Alder reaction, employing vinyl Bpin as a bifunctional reagent in two distinct roles: as an organoboron nucleophile for cross-coupling and as a Diels–Alder dienophile. Merging these two reactions enables a rapid and operationally simple synthesis of functionalized carbocycles in good yield. The effect of the organoboron subtype on Diels–Alder regioselectivity was investigated and postsynthetic modifications were carried out on a model substrate. The potential for a complementary Heck/Diels–Alder process was also assessed.

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4

Cai, Quan, Xu-Ge Si, and Zhi-Mao Zhang. "Asymmetric Inverse-Electron-Demand Diels–Alder Reactions of 2-Pyrones by Lewis Acid Catalysis." Synlett 32, no. 10 (January 24, 2021): 947–54. http://dx.doi.org/10.1055/a-1371-4391.

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AbstractDiels–Alder reactions of 2-pyrones with alkenes can provide highly functionalized [2,2,2]-bicyclic lactones under mild reaction conditions. Synthetic utilizations of these reactions have been well demonstrated in natural-product synthesis. Although several catalytic asymmetric strategies have been realized, current research in this area is still largely underdeveloped. Recent advances in enantioselective inverse-electron-demand Diels–Alder reactions with Lewis acid catalysis are reviewed.1 Introduction2 State of the Art of Enantioselective Diels–Alder Reactions of 2-Pyrones by Lewis Acid Catalysis3 Enantioselective Synthesis of Arene cis-Dihydrodiols by Diels–Alder/Retro-Diels–Alder Reactions of 2-Pyrones4 Enantioselective Synthesis of cis-Decalin Derivatives by Diels–Alder Reactions of 2-Pyrones5 Conclusions

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5

Fedevych, Maria. "α-Unsaturated Acids in Diels-Alder Reaction." Chemistry & Chemical Technology 5, no. 4 (December 15, 2011): 373–75. http://dx.doi.org/10.23939/chcht05.04.373.

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6

Rao, Nagaraj. "ASYMMETRIC ORGANOCATALYSIS." INDIAN DRUGS 58, no. 10 (December 16, 2021): 5–6. http://dx.doi.org/10.53879/id.58.10.p0005.

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Dear Reader, Two basic reactions that were taught to us in the organic chemistry courses were the aldol condensation reaction and the Diels-Alder reaction. In aldol condensation, discovered by the French chemist Charles Wurtz in 1872, an enolate ion reacts with a carbonyl compound in the presence of an acid/ base catalyst to form a β-hydroxy aldehyde or a β-hydroxy ketone, usually followed by dehydration to give a conjugated enone. If the enolate ion and the carbonyl group are present in the same molecule, then the aldol reaction is intramolecular. It is an extremely useful carbon-carbon bond-forming reaction. The Diels-Alder reaction, discovered in 1928 by the German chemist Otto Diels and his student Kurt Alder, is the reaction between a conjugated diene and an alkene, a so-called dienophile, to form an unsaturated six-membered ring. It is called a cycloaddition reaction, since the reaction involves the formation of a cyclic product via a cyclic transition state. Uncatalysed Diels– Alder reactions usually require extended reaction times at elevated pressures and temperatures with the formation of by-products, hence various catalysts are employed. The Diels-Alder reaction also has great industrial relevance and the discoverers were crowned with the 1950 Nobel Prize in Chemistry. The aldol condensation reaction and the Diels-Alder reaction typically require catalysts, basically Brønsted acids, Brønsted bases, Lewis acids or Lewis bases. This triggered the minds of Dr. David MacMillan and Dr. Benjamin List for different reasons at different locations in USA around not so different times, more than twenty years ago, culminating in their being jointly awarded the Nobel Prize in Chemistry for this year.

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7

Xia, Qingchun, Yan Liu, Zijian Li, Wei Gong, and Yong Cui. "A Cr(salen)-based metal–organic framework as a versatile catalyst for efficient asymmetric transformations." Chemical Communications 52, no. 89 (2016): 13167–70. http://dx.doi.org/10.1039/c6cc06019f.

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A novel Cr(salen)-based metal–organic framework (MOF) is constructed, which is shown to be a versatile heterogeneous catalyst for a series of important asymmetric transformations including Nazarov cyclization reaction, aminolysis reaction, Diels–Alder and hetero Diels–Alder reactions with the highest ee up to 99%.

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8

Lee, Chi-Sing, Guangyan Du, Gaopeng Wang, Wenjing Ma, Qianqian Yang, Wenli Bao, Xuefeng Liang, and Lizhi Zhu. "Syntheses of Diverse Natural Products via Dual-Mode Lewis Acid Induced Cascade Cyclization Reactions." Synlett 28, no. 12 (April 6, 2017): 1394–406. http://dx.doi.org/10.1055/s-0036-1588777.

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The σ/π-binding properties of a series of Lewis acids was studied using DFT calculations. The results led to the identification of Zn(II)/In(III) as a suitable dual-mode Lewis acid for use in promoting cascade cyclization reactions. Based on this finding, we developed three new types of dual-mode Lewis acid induced cascade cyclization reactions and have demonstrated the utilities of each process in natural product synthesis.1 Introduction2 Dual-Mode Lewis Acids3 Prins/Conia-Ene Cascade Reaction and its Applications4 Diels–Alder/Carbocyclization Cascade Reaction and Applications4.1 First Generation Diels–Alder/Carbocyclization Cascade Reaction and its Application4.2 Second Generation Diels–Alder/Carbocyclization Cascade Reaction and its Applications5 Michael/Conia-Ene Cascade Reaction and its Applications6 Conclusion

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9

Breton, Gary W., and Kenneth L. Martin. "Exploring the Limits of Reactivity of N-Methyl-1,2,4-triazoline-3,5-dione (MeTAD) with Disubstituted Bicycloalkadienes in the Homo-Diels–Alder Reaction." Organics 4, no. 1 (December 31, 2022): 41–48. http://dx.doi.org/10.3390/org4010002.

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The [2+2+2] cycloaddition (homo-Diels–Alder reaction) of N-substituted 1,2,4-triazoline-3,5-diones (TADs) with bicycloalkadienes produces strained heterocyclic compounds. A reaction with the unsubstituted dienes occurs readily to produce only the expected homo-Diels–Alder adducts. However, previous work in the literature showed that the attachment of a single electron-withdrawing group to the diene system results in the formation of not only the expected homo-Diels–Alder adducts, but also interesting “insertion” products. To probe the limits of reactivity of these diene systems, we investigated the reaction of N-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with bicycloalkadienes substituted with two electron-withdrawing groups, i.e., two carbomethoxy or two cyano groups. We hoped to learn whether the reaction still proceeded, and if so, whether the homo-Diels–Alder adducts and/or other types of products were formed. We found that a reaction between MeTAD and the dienes takes place upon substitution with two carbomethoxy groups, albeit at a considerably slower rate than other reactions. The only products observed were the homo-Diels–Alder adducts. However, attachment of two CN groups completely inhibited reactivity.

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10

Wang, Shu-Wen, Wei-Si Guo, Li-Rong Wen, and Ming Li. "A new approach to pyridines through the reactions of methyl ketones with 1,2,4-triazines." RSC Adv. 4, no. 103 (2014): 59218–20. http://dx.doi.org/10.1039/c4ra11294f.

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A new route to prepare pyridine derivatives based on inverse electron demand Diels–Alder/retro-Diels–Alder reactions of ketones with 1,2,4-triazines is reported, which is complementary to the classical Boger reaction.

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11

Carneiro de Oliveira, Jamerson, Marie-Pierre Laborie, and Vincent Roucoules. "Thermodynamic and Kinetic Study of Diels–Alder Reaction between Furfuryl Alcohol and N-Hydroxymaleimides—An Assessment for Materials Application." Molecules 25, no. 2 (January 7, 2020): 243. http://dx.doi.org/10.3390/molecules25020243.

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The study of Diels–Alder reactions in materials science is of increasing interest. The main reason for that is the potential thermoreversibility of the reaction. Aiming to predict the behavior of a material modified with maleimido and furyl moieties, 1H NMR and UV-Vis solution studies of the Diels–Alder reaction between furfuryl alcohol and two N-hydroxymaleimides are explored in the present study. Rate constants, activation energy, entropy, and enthalpy of formation were determined from each technique for both reacting systems. Endo and exo isomers were distinguished in 1H NMR, and the transition from a kinetic, controlled Diels–Alder reaction to a thermodynamic one could be observed in the temperature range studied. A discussion on the effect of that on the application in a material was performed. The approach selected considers a simplified equilibrium of the Diels–Alder reaction as the kinetic model, allowing materials scientists to evaluate the suitability of using the reacting molecules for the creation of thermoresponsive materials. The proposed approach determines the kinetic constants without the direct influence of the equilibrium constant value, thereby allowing a more objective data analysis. The effects of the selection of kinetic model, analytical method, and data treatment are discussed.

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12

Yang, Zhongyue, Song Yang, Peiyuan Yu, Yanwei Li, Charles Doubleday, Jiyong Park, Ashay Patel, et al. "Influence of water and enzyme SpnF on the dynamics and energetics of the ambimodal [6+4]/[4+2] cycloaddition." Proceedings of the National Academy of Sciences 115, no. 5 (January 18, 2018): E848—E855. http://dx.doi.org/10.1073/pnas.1719368115.

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SpnF is the first monofunctional Diels–Alder/[6+4]-ase that catalyzes a reaction leading to both Diels–Alder and [6+4] adducts through a single transition state. The environment-perturbed transition-state sampling method has been developed to calculate free energies, kinetic isotope effects, and quasi-classical reaction trajectories of enzyme-catalyzed reactions and the uncatalyzed reaction in water. Energetics calculated in this way reproduce the experiment and show that the normal Diels–Alder transition state is stabilized by H bonds with water molecules, while the ambimodal transition state is favored in the enzyme SpnF by both intramolecular hydrogen bonding and hydrophobic binding. Molecular dynamics simulations show that trajectories passing through the ambimodal transition state bifurcate to the [6+4] adduct and the Diels–Alder adduct with a ratio of 1:1 in the gas phase, 1:1.6 in water, and 1:11 in the enzyme. This example shows how an enzyme acts on a vibrational time scale to steer post-transition state trajectories toward the Diels–Alder adduct.

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13

Frank, Scott A., Andrea B. Works, and William R. Roush. "Studies on the synthesis of the decahydro-as-indacene ring system of (-)-spinosyn A via transannular Diels-Alder reactions of substituted (E,E,E)-cyclododeca-1,6,8-trienes." Canadian Journal of Chemistry 78, no. 6 (June 1, 2000): 757–71. http://dx.doi.org/10.1139/v00-045.

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Stereoselective syntheses of decahydro-as-indacenes 31 and 54 are reported. The key features of our syntheses of 31 and 54 are the tandem Ireland-Claisen ring contraction of lactones 29 and 38 followed by the transannular Diels-Alder cyclization of cyclododecatrienes 30 and 35. Transition state modeling of both the transannular Diels-Alder reaction and the Ireland-Claisen ring contraction using PCModel is also described.Key words: transannular Diels-Alder reactions, tandem reactions, Claisen ring contraction, Spinosyn A, synthetic study.

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14

TAKAGUCHI, YUTAKA, TAKAAKI TSUBOI, YUUKI SAKO, and SADAO TSUBOI. "SYNTHESIS OF FULLERODENDRON AND ITS PHOTOCATALITIC ACTIVITY." International Journal of Nanoscience 05, no. 04n05 (August 2006): 593–97. http://dx.doi.org/10.1142/s0219581x0600484x.

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A newly designed fullerodendron was synthesized in good yield (84%) by the use of a Diels-Alder reaction of C 60 with an anthryl dendron. Interestingly, the fullerodendron acts as a new catalyst that uses oxygen and light to generate singlet oxygen (1 O 2). The dendron facilitates various types of singlet oxygenation reactions including ene reaction, Diels-Alder reaction, and oxidation of phenol and sulfide.

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15

Cao, Min-Hui, Nicholas J. Green, and Sheng-Zhen Xu. "Application of the aza-Diels–Alder reaction in the synthesis of natural products." Organic & Biomolecular Chemistry 15, no. 15 (2017): 3105–29. http://dx.doi.org/10.1039/c6ob02761j.

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16

Werstiuk, Nick Henry, and Wojciech Sokol. "Density functional theory computational study on Diels–Alder reactions of cyclopentadiene with selected vinylsilanes and methylenecyclopropane." Canadian Journal of Chemistry 89, no. 3 (February 2011): 409–14. http://dx.doi.org/10.1139/v10-167.

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Aimed at predicting relative reactivities, density functional theory (DFT) calculations were carried out on a series of Diels–Alder reactions involving silylvinyl derivatives reacting with cyclopentadiene as part of a synthetic research project. Using three reactions for which experimental rate data are available to calibrate our calculations, we computationally pinpointed the best synthetic route to bicyclo[2.2.1]hept-5-ene-2,2-diylbis(trimethylsilane) (1). The synthesis begins with the Diels–Alder reaction of cyclopentadiene (2) with commercially available (1-bromovinyl)trimethylsilane (6).

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17

Liu, Zhang, Wang, Zan, and Zhang. "The Role of Iodine Catalyst in the Synthesis of 22-Carbon Tricarboxylic Acid and Its Ester: A Case Study." Catalysts 9, no. 12 (November 20, 2019): 972. http://dx.doi.org/10.3390/catal9120972.

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Here, 22-carbon tricarboxylic acid (C22TA) and its ester (C22TAE) were prepared via the Diels–Alder reaction of polyunsaturated fatty acids (PUFAs) and their esters (PUFAEs) as dienes with fumaric acid (FA) and dimethyl fumarate (DF) as dienophiles, respectively. The role of an iodine catalyst for the synthesis of C22TA and C22TAE in the Diels–Alder type reaction was investigated using a spectroscopic approach. The chemical structures of the products were characterized using proton nuclear magnetic resonance (1H-NMR) and electrospray ionization mass spectrometry (ESI-MS) analysis. Results showed that nonconjugated dienes can react with dienophiles through a Diels–Alder reaction with an iodine catalyst, and that iodine transformed the nonconjugated double bonds of dienes into conjugated double bonds via a radical process. DF was more favorable for the Diels–Alder reaction than FA. This was mainly because the dienophile DF contained an electron-withdrawing substituent, which reduced the highest and lowest occupied molecular orbital (HOMO–LUMO) energy gap and accelerated the Diels–Alder reaction. By transforming nonconjugated double bonds into conjugated double bonds, iodine as a Lewis acid increased the electron-withdrawing effect of the carbonyl group on the carbon–carbon double bond and reduced the energy difference between the HOMO of diene and the LUMO of dienophile, thus facilitating the Diels–Alder reaction.

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18

He, Siyang, and Guido Kickelbick. "Reversible Diels–Alder Reactions with a Fluorescent Dye on the Surface of Magnetite Nanoparticles." Molecules 26, no. 4 (February 7, 2021): 877. http://dx.doi.org/10.3390/molecules26040877.

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Diels–Alder reactions on the surface of nanoparticles allow a thermoreversible functionalization of the nanosized building blocks. We report the synthesis of well-defined magnetite nanoparticles by thermal decomposition reaction and their functionalization with maleimide groups. Attachment of these dienophiles was realized by the synthesis of organophosphonate coupling agents and a partial ligand exchange of the original carboxylic acid groups. The functionalized iron oxide particles allow a covalent surface attachment of a furfuryl-functionalized rhodamine B dye by a Diels–Alder reaction at 60 °C. The resulting particles showed the typical fluorescence of rhodamine B. The dye can be cleaved off the particle surface by a retro-Diels–Alder reaction. The study showed that organic functions can be thermoreversibly attached onto inorganic nanoparticles.

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19

Bercich, Mark D., Richard C. Cambie, and Peter S. Rutledge. "Experiments Directed Towards the Synthesis of Anthracyclinones. XXXIV Hetero-Diels - Alder Reactions Using Chiral Boron and Titanium Reagents." Australian Journal of Chemistry 52, no. 9 (1999): 851. http://dx.doi.org/10.1071/ch98181.

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Reactions between benzaldehyde or o-anisaldehyde and a series of silyloxy dienes catalysed by the chiral acyl- oxyborane (CAB) complex (4) give high yields of enantioselective products from a Mukaiyama aldol rather than a hetero-Diels–Alder reaction. Attempts to effect a similar catalytic reaction with anthraquinone aldehydes were unsuccessful but use of 2 equiv. of the CAB complex (1) followed by cyclization promotes a formal hetero- Diels–Alder reaction between the aldehyde (7) and the diene (12) to give the dihydropyrone (24) in 45% yield and with a 79% e.e. in favour of the 2'R enantiomer. Hetero-Diels–Alder reactions between the aldehyde (7) and the diene (12) using the chiral titanium complexes Ti[(R)-BINOL]Cl 2 , Ti[(R,R)-TADDOL]Cl 2 and Ti[(R)-BINOL] 2 have been investigated. The first two complexes promote the reaction at −30 and −78° respectively but with low induced enantioselectivities.

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20

Carlini, Rina, Kerianne Higgs, Nicholas Taylor, and Russell Rodrigo. "Diels–Alder adducts of ortho-benzoquinones: rearrangements and further transformations." Canadian Journal of Chemistry 75, no. 6 (June 1, 1997): 805–16. http://dx.doi.org/10.1139/v97-097.

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ortho-Benzoquinones substituted with an electron-withdrawing group (EWG = CO2Me, COSMe, COCH3, CHO) at C-3 or C-4 react as dienophiles at the C3—C4 double bond in Diels–Alder reactions with several dienes, with predictable regiochemistry. The adducts undergo migration of the "angular" EWG substituent with concomitant aromatization to produce substituted catechols. The bicyclic products can be oxidized in situ and annelated by a further Diels–Alder reaction to yield 9,10-phenanthraquinone systems. When (2E)-2,4-pentadienol is employed as the diene in the second cycloaddition, reaction of the alcoholic hydroxyl group with one of the quinone carbonyl groups results in the production of tetracyclic lactols 22a, 22b, and 23. Keywords: benzoquinone, Diels–Alder, rearrangement, phenanthraquinone, phenanthrofuran.

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21

Benmeddah, Amel, Didier Villemin, Bachir Mostefa-Kara, Nathalie Bar, and Remi Legay. "Catalyst-free Diels–Alder reactions of vinylphosphonates with cyclopentadienones." Canadian Journal of Chemistry 95, no. 8 (August 2017): 871–79. http://dx.doi.org/10.1139/cjc-2017-0267.

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The unprecedented thermal Diels–Alder reaction of the diethyl vinylphosphonate and diethyl styrylphosphonate with various cyclopentadienones is described. In these Diels–Alder reactions, catalysis was not required and the corresponding cycloadducts derivatives were obtained. The tetraethyl vinylidene-1,1-bis-phosphonate was found to be less reactive than monophosphonates with the same cyclopentadienones.

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22

Goh, Yit W., and Jonathan M. White. "Structure Correlation Study of Some Diels–Alder Cycloadducts of Anthracene." Australian Journal of Chemistry 62, no. 5 (2009): 419. http://dx.doi.org/10.1071/ch09050.

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Crystal structures of some Diels–Alder cycloadducts of anthracene and a variety of dienophiles reveal structural effects consistent with the manifestation of the early stages of the retro Diels–Alder reaction in the ground state structure. The symmetrical cycloadducts 3 and 4 reveal a qualitative relationship between structure and reactivity, whereas the cycloadducts of 9-methoxyanthracene show structural effects suggestive of the early stages of an asynchronous retro Diels–Alder reaction.

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23

Sultan, Mujeeb A., and Usama Karama. "Substituent Effects on Regioselectivity of the Diels-Alder Reactions: Reactions of 10-Allyl-1,8-dichloroanthracene with 2-Chloroacrylonitrile, 1-Cyanovinyl Acetate and Phenyl Vinyl Sulfone." Journal of Chemistry 2016 (2016): 1–5. http://dx.doi.org/10.1155/2016/3943060.

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Diels-Alder reaction of 10-allyl-1,8-dichloroanthracene (3) with 2-chloroacrylonitrile (4) and 1-cyanovinyl acetate (5) gives exclusively theorthoisomer while its reaction with phenyl vinyl sulfone (10) yields a mixture of two isomeric adducts with priority toorthoisomer. The reactions proceeded under microwave condition in xylene. Configurations of these isomers have been assigned with the help of NMR spectra. The results indicated that the steric effect is dominating toward the isomer regioselectivity in the Diels-Alder reaction of the present compounds.

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24

Heller, Douglas P., Daniel R. Goldberg, Hongqiao Wu, and William D. Wulff. "An examination of VANOL, VAPOL, and VAPOL derivatives as ligands for asymmetric catalytic Diels–Alder reactions." Canadian Journal of Chemistry 84, no. 10 (October 1, 2006): 1487–503. http://dx.doi.org/10.1139/v06-124.

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Several derivatives of the vaulted biaryl ligand VAPOL were prepared and evaluated as chiral ligands for aluminum Lewis acids in the catalytic asymmetric Diels–Alder reactions of methyl acrylate and methacrolein with cyclopentadiene. The substituents on VAPOL were introduced into the 6- and 6′-positions in an effort to further extend the chiral pocket of the major groove, which contains the phenol functions at the 4- and 4′-positions. The set of four new ligands that have been prepared have the following groups introduced into the 6- and 6′-positions of VAPOL: bromide, methyl, phenyl and 3,5-di-t-butylphenyl. All of these ligands give lower asymmetric inductions than the unsubstituted VAPOL for the Diels–Alder reactions of both methyl acrylate and methacrolein. The positive cooperativity of added carbonyl compounds on the autoinduction in the Diels–Alder reaction of methyl acrylate and cyclopentadiene were also investigated with the VANOL and VAPOL ligands as well as the 6,6′-dibromo and 6,6′-diphenyl derivatives of VAPOL. Only the reaction with VAPOL showed any significant positive cooperativity. The reaction with VANOL was sluggish at –78 °C, but at higher temperatures, the reaction did exhibit positive cooperativity that was similar to that of VAPOL. Finally, no positive cooperativity was observed with the VAPOL ligand for the reaction of methacrolein and cyclopentadiene.Key words: Diels–Alder, asymmetric catalysis, vaulted biaryl ligands, VANOL, VAPOL.

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25

Silva, Eduarda, Artur Silva, and Djenisa Rocha. "Diels–Alder Reactions of 1,2-Dihydropyridines: An Efficient Tool for the Synthesis of Isoquinuclidines." Synthesis 50, no. 09 (April 4, 2018): 1773–82. http://dx.doi.org/10.1055/s-0037-1609418.

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The Diels–Alder reaction of 1,2-dihydropyridines with different dienophiles is a well-established and straightforward method for the synthesis of isoquinuclidines. Nevertheless, the enantioselective preparation of isoquinuclidines using organocatalysts or organometallic catalysts is rather unexplored. This succinct review offers readers an overall perspective of the most important recent developments and concepts related to this topic.1 Introduction2 Asymmetric Diels–Alder Reaction of 1,2-Dihydropyridines2.1 Transition-Metal-Catalyzed Reactions2.2 Organocatalyzed Reactions3 Diels–Alder Reaction of 1,2-Dihydropyridines in the Synthesis of Biologically Valuable Compounds4 Conclusion

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26

Cameron, DW, RW Read, and J. Stavrakis. "Reactions of Dimethyl (2'-Oxopropylidene)Propanedioate and Dimethyl (3'-Bromo-2'-oxopropylidene)propanedioate, Two Highly Electrophilic Trisubstituted Alkenes." Australian Journal of Chemistry 40, no. 11 (1987): 1831. http://dx.doi.org/10.1071/ch9871831.

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The keto diester, dimethyl (2'-oxopropylidene)propanedioate, and its new 3'-bromo derivative have been made to react with a variety of nucleophilic reagents. Low molecular weight products have been obtained efficiently by processes involving conjugate addition, Diels-Alder reaction, Diels-Alder reaction having inverse electron demand, or ene reaction. Regiochemistry of the reactions is controlled by the dominant withdrawing effect of the two geminal ester groups. The amine addition products of the bromo keto diester were found to undergo a novel secondary dehydrobromination reaction under alkaline conditions.

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27

Ozawa, Takuya, Takuya Kurahashi, and Seijiro Matsubara. "Dehydrogenative Diels–Alder Reaction." Organic Letters 13, no. 19 (October 7, 2011): 5390–93. http://dx.doi.org/10.1021/ol202283d.

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28

Wagner, Gabriele, Nadia Vahdati, Ashley Howkins, and Louisa Cubitt. "Reaction Prediction using Density Functional Theory Calculations: A Study into the Synthesis of Safranal via Diels-Alder Reactions." Zeitschrift für Naturforschung B 66, no. 11 (November 1, 2011): 1141—s1241. http://dx.doi.org/10.1515/znb-2011-1110.

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Two pathways for the synthesis of safranal (2,6,6-trimethyl-cyclohexa-1,3-diene-1-carbaldehyde) via a Diels-Alder reaction are proposed and analyzed for their feasibility by Density Functional Theory (DFT) calculations on a B3LYP/6-31G* level of theory. Pathway A involving the reaction of 3-methyl-2-butenal with 4-methoxypenta-1,3-diene is predicted to produce the desired regioisomers, although with low stereoselectivity. Due to the high activation barrier (23 kcal mol−1), the reaction will require harsher conditions than the related known reaction of Z-2-butenal and 1-methoxy-1,3- butadiene with a calculated ΔEa of 17 kcal mol−1. Replacement of the methoxy group at the diene by OAc, OSiMe3 or pyrrolidinyl does not enhance the reactivity any further. Preliminary experiments confirm these results, although the reaction conditions need to be improved for the reaction to be of synthetic use. In the reaction of methoxyethene with 3-formyl-2,4-dimethylpenta-1,3-diene (pathway B), the homo- and hetero-Diels-Alder pathways were compared. The desired homo-Diels-Alder reaction is predicted to give the correct regioisomer in an exothermic reaction. However, the activation barrier is high (30 kcal mol−1) and the reaction unlikely to proceed. The hetero-Diels-Alder reaction requires less activation energy (23 kcal mol−1) and is expected to dominate, although the thermodynamic driving force is low. The preferred regioisomeric product is the 2-methoxy-3,4-dihydropyran, in agreement with related reactions studied experimentally

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29

Soares, Maria I. L., Ana L. Cardoso, and Teresa M. V. D. Pinho e Melo. "Diels–Alder Cycloaddition Reactions in Sustainable Media." Molecules 27, no. 4 (February 15, 2022): 1304. http://dx.doi.org/10.3390/molecules27041304.

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Diels–Alder cycloaddition reaction is one of the most powerful strategies for the construction of six-membered carbocyclic and heterocyclic systems, in most cases with high regio- and stereoselectivity. In this review, an insight into the most relevant advances on sustainable Diels–Alder reactions since 2010 is provided. Various environmentally benign solvent systems are discussed, namely bio-based derived solvents (such as glycerol and gluconic acid), polyethylene glycol, deep eutectic solvents, supercritical carbon dioxide, water and water-based aqueous systems. Issues such as method’s scope, efficiency, selectivity and reaction mechanism, as well as sustainability, advantages and limitations of these reaction media, are addressed.

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30

Kell, Arnold J., Christopher C. Montcalm, and Mark S. Workentin. "Photogeneration of a diene template for surface DielsAlder reactions: Photoenolization of an ortho-methyl-benzophenone-modified Au cluster." Canadian Journal of Chemistry 81, no. 6 (June 1, 2003): 484–94. http://dx.doi.org/10.1139/v03-031.

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A series of monolayer-protected clusters (MPCs) modified with a photoreactive [4-(11-mercaptoundecyl)-phenyl](2-methylphenyl)methanone (1) moiety have been prepared where 1 is co-absorbed to the MPC surface with dodecanethiol, octadecanethiol, or 11-mercaptoundecanoic acid methyl ester. Upon irradiation the MPC-anchored 1 reacts efficiently through its triplet excited states, yielding 1,4-biradicals that collapse to synthetically useful, long-lived photodienol intermediates, which can be efficiently trapped in DielsAlder type chemistry by dienophiles namely, dimethyl acetylenedicarboxylate (DMAD). In all cases the DielsAlder trapping of the dienol occurred efficiently resulting in >60% conversion to the DielsAlder adduct. This indicates that the local environment surrounding 1 did not influence its ability to react via the DielsAlder reaction; however, the reaction could not be taken to completion. The inability to react completely is attributed to 1 binding to distinct sites on the MPC core; there are edge, vertice, and terrace sites. Selective population of these specific sites and the subsequent irradiations show that MPCs with 1 anchored predominantly at edge and vertice sites results in an extent of reaction of 85 ± 3%, whereas selectively populating the terrace sites results in an extent of reaction of 36 ± 2%. These results suggest that 1 anchored to edge and vertice sites is more reactive to the DielsAlder reaction than that involving terrace sites.Key words: monolayer protected cluster, site selective reactivity, DielsAlder, photochemistry.

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31

Bauer, John B., Fatima Diab, Cäcilia Maichle-Mössmer, Hartmut Schubert, and Holger F. Bettinger. "Synthesis of the [11]Cyclacene Framework by Repetitive Diels–Alder Cycloadditions." Molecules 26, no. 10 (May 20, 2021): 3047. http://dx.doi.org/10.3390/molecules26103047.

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The Diels–Alder cycloaddition between bisdienes and bisdienophile incorporating the 7-oxa-bicyclo[2.2.1]heptane unit are well known to show high diastereoselectivity that can be exploited for the synthesis of molecular belts. The related bisdiene 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octene is a valuable building block for the synthesis of photoprecursors for acenes, but it has not been employed for the synthesis of molecular belts. The present work investigates by computational means the Diels–Alder reaction between these bisdiene building blocks with syn-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene, which shows that the diastereoselectivity of the Diels–Alder reaction of the etheno-bridged bisdiene is lower than that of the epoxy-bridged bisdiene. The reaction of the etheno-bridged bisdiene and syn-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene in 2:1 ratio yields two diastereomers that differ in the orientation of the oxa and etheno bridges based on NMR and X-ray crystallography. The all-syn diastereomer can be transformed into a molecular belt by inter- and intramolecular Diels–Alder reactions with a bifunctional building block. The molecular belt could function as a synthetic intermediate en route to a [11]cyclacene photoprecursor.

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32

Bittner, Bożena, Ewa Janus, and Eugeniusz Milchert. "N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and Lewis acids — catalytic systems for Diels-Alder reaction." Open Chemistry 9, no. 1 (February 1, 2011): 192–98. http://dx.doi.org/10.2478/s11532-010-0138-4.

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AbstractA comparative study of the Diels-Alder reactions between cyclopentadiene (1) and dienophiles (2 a–c) in N-hexylpyridinium bis(trifluoromethylsulfonyl)imide in a temperature range of 20–45°C is reported. The reaction rate constants and activation energies were calculated. Moreover, the catalytic systems based on N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and Lewis acids were tested as a reaction media to perform the Diels-Alder reaction. Yb, Y, Mg, Zn triflates and chlorides (0.005 to 0.1 mmol) were used as catalysts. The recycling of catalytic system consisted of YCl3 and ionic liquid was performed.

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33

Escalante, Carlos H., Eder I. Martínez-Mora, Carlos Espinoza-Hicks, Alejandro A. Camacho-Dávila, Fernando R. Ramos-Morales, Francisco Delgado, and Joaquín Tamariz. "Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole." Beilstein Journal of Organic Chemistry 16 (June 17, 2020): 1320–34. http://dx.doi.org/10.3762/bjoc.16.113.

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A highly regio-, chemo- and stereoselective divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles is herein described, starting from 2-formylpyrrole and employing Diels–Alder and Heck arylation reactions. 3-(N-Benzyl-2-pyrrolyl)acrylates and 4-(pyrrol-2-yl)butenones underwent a highly endo-Diels–Alder cycloaddition with maleimides to furnish octahydropyrrolo[3,4-e]indoles, which served as precursors in the regioselective synthesis of aza-polycyclic skeletons via an intramolecular Heck arylation reaction. Through the latter reaction, the 3-(N-benzyl-2-pyrrolyl)acrylates give rise to 3-(pyrrolo[2,1-a]isoindol-3-yl)acrylates. A further oxidative aromatization of the polycyclic intermediates provides the corresponding polycyclic pyrrolo-isoindoles and isoindolo-pyrrolo-indoles. A theoretical study on the stereoselective Diels–Alder reactions, carried out by calculating the endo/exo transition states, revealed the assistance of non-covalent interactions in governing the endo stereocontrol.

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34

Kirchhof, Susanne, Andrea Strasser, Hans-Joachim Wittmann, Viktoria Messmann, Nadine Hammer, Achim M. Goepferich, and Ferdinand P. Brandl. "New insights into the cross-linking and degradation mechanism of Diels–Alder hydrogels." Journal of Materials Chemistry B 3, no. 3 (2015): 449–57. http://dx.doi.org/10.1039/c4tb01680g.

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35

Srivastava, Vivek. "Ionic-Liquid-Mediated MacMillan’s Catalyst for Diels-Alder Reaction." Journal of Chemistry 2013 (2013): 1–5. http://dx.doi.org/10.1155/2013/954094.

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Ionic liquids were used to enhance as well as recycle the MacMillan's catalyst1for the Diels-Alder reaction. Using our developed protocol, Diels-Alder adducts were obtained in good yields and selectivities along the 6 times recycling of MacMillan's imidazolidinone catalyst1. Synthesis of steroid4is the major outcome of our developed protocol.

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36

de la Cruz, Ricardo A., Francisco X. Talamás, Alfredo Vázquez, and Joseph M. Muchowski. "Total synthesis of mycophenolic acid." Canadian Journal of Chemistry 75, no. 6 (June 1, 1997): 641–45. http://dx.doi.org/10.1139/v97-078.

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A total synthesis of mycophenolic acid is reported. Diels–Alder reaction of [5-methoxy-3-(1-methoxypropenyl)-4,5-dihydrofuran-2-yloxy]-trimethylsilane with 3-benzenesulfinyl-5H-furan-2-one afforded the hexasubstituted nucleus. The side chain was constructed from the unveiled aldehyde. Keywords: mycophenolic acid, Diels–Alder reaction, pentasubstituted diene.

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37

Scheerer, Jonathan, Jill Williamson, and Emily Smith. "A Merged Aldol Condensation, Alkene Isomerization, Cycloaddition/Cycloreversion Sequence Employing Oxazinone Intermediates for the Synthesis of Substituted Pyridines." Synlett 28, no. 10 (February 23, 2017): 1170–72. http://dx.doi.org/10.1055/s-0036-1588729.

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A domino reaction sequence has been evaluated that begins with union of novel dihydrooxazinone precursors with 2-alkynyl-substituted benzaldehyde components through aldol condensation. Ensuing operations, including alkene isomerization, Diels–Alder, and retrograde Diels–Alder with loss of CO2 occurs in the same reaction vessel to provide polysubstituted tricyclic pyridine products.

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38

Jankowski, Christopher K., Gaëtan LeClair, Jacqueline MR Bélanger, Jocelyn RJ Paré, and Marie-Rose VanCalsteren. "Microwave-assisted Diels-Alder synthesis." Canadian Journal of Chemistry 79, no. 12 (December 1, 2001): 1906–9. http://dx.doi.org/10.1139/v01-183.

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The synthesis of isoquinolinone carboxylates was performed using arecoline or its isomer N-methyl tetrahydro pyridine carboxylate with Danishefsky's diene via thermal or microwave assisted Diels-Alder reaction. The comparison of both condensation modes showed that the microwave method not only afforded higher yields of the adducts, but also lead to the formation of a new α,β-unsaturated pyridyl ketone. All structures were identified with the help of high resolution 2D NMR.Key words: Diels-Alder microwave assisted reaction, microwave synthesis, Michael, diene, isoquinoline carboxylate synthesis, Danishefsky diene synthesis, MAP Diels-Alder2.

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39

Xu, Yao-Chang, Andrew L. Roughton, Raymond Plante, Solo Goldstein, and Pierre Deslongchamps. "Stereocontrolled construction of 1,7-dimethyl A.B.C.[6.6.6] tricycles. Part I. Transannular Diels–Alder reactions of 14-membered macrocycles containing trans-dienophiles." Canadian Journal of Chemistry 71, no. 8 (August 1, 1993): 1152–68. http://dx.doi.org/10.1139/v93-152.

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Transannular Diels–Alder reactions of 14-membered macrocyclic trienes possessing a methyl substituent on both the diene and dienophile moiety have been investigated. Macrocyclic structures 1a, 1b, and 1c having cis-trans-trans (CTT), trans-cis-trans (TCT), and trans-trans-trans (TTT) geometries could be stereoselectively constructed by coupling appropriately functionalized dienes 5 and dienophile 4 following an intramolecular displacement of an allylic halide by the anion of an appropriately located dimethyl malonate unit. The transannular Diels–Alder reaction performed on 1a led to a mixture of four major tricyclic products, including 34 possessing the unexpected trans-anti-cis (TAC) stereochemistry. When heated at 300 °C, macrocycle 1b underwent an unique conversion via an ene–retroene, Diels–Alder process, producing the unexpected tricycle 41 (racemic form) containing five contiguous chiral centers. A rationale for the above experimental facts is presented. In contrast to the previous results, the transannular Diels–Alder reaction of macrocycle 1c was straightforward, producing a 95% isolated yield of trans-anti-cis (TAC) tricycle 34. This investigation demonstrates a general methodology for the stereocontrolled synthesis of 1,2-dimethyl A.B.C[6.6.6] tricyclic compounds, which are potential precursors to polycyclic natural products such as steroids and terpenes.

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40

Zakharova, Daria V., Zalina A. Lok’yaeva, Alexander A. Pavlov, and Alexander V. Polezhaev. "New Chain Extenders for Self-Healing Polymers." Key Engineering Materials 899 (September 8, 2021): 628–37. http://dx.doi.org/10.4028/www.scientific.net/kem.899.628.

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We present here a small series of compounds designed to modify the polymer chain of various polyurethanes in order to introduce a structural fragment with the ability of thermally-triggered reversible covalent interactions. Bismaleimides (2a-2e) were synthesized from commercially available aromatic and aliphatic symmetric diamines (1a-1e) and were further introduced into the Diels-Alder reaction with furfuryl alcohol as dienophiles. The Diels-Alder adducts (3a-3e) were obtained as a mixture of endo- and exo-isomer. The presence of symmetrical hydroxyl groups in the structure of the obtained compounds makes them suitable as chain extenders of low molecular weight diisocyanate prepolymers. The presence of a thermally reversible Diels-Alder reaction adduct in the structure of potential chain-extenders opens a possibility to create unique materials with self-healing properties. All compounds obtained were characterized by 1H, 13C NMR, ESI-HRMS, and IR spectroscopy. The thermochemical parameters of the reverse Diels-Alder reaction were established using DSC analysis.

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41

Ward, Dale E., and Yuanzhu Gai. "Synthesis of 10-methyl-Δ4-octalins by Diels–Alder reactions of 2H-thiopyran surrogates for 1-ethenyl-2-methylcyclohexene." Canadian Journal of Chemistry 75, no. 6 (June 1, 1997): 681–93. http://dx.doi.org/10.1139/v97-082.

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Diels–Alder reactions of 1-ethenyl-2-methylcyclohexene derivatives could be a versatile route to a variety of natural product skeletons that possess a 10-methyldecalin substructure with additional substitution at C-8 and C-9. These dienes are unreactive due (in part) to the presence of the vinyl methyl group, which destabilizes the necessary s-cis conformation. The use of 2H-thiopyran diene surrogates for 1-ethenyl-2-methylcyclohexene is investigated. The desired Diels–Alder adducts were not obtained by reaction of 6,7,8,8a-tetrahydro-5,5-dimethyl-3-tris(1-methylethyl)silyloxy-1H-2-benzothiopyran (7c) or 1,5,7,8-tetrahydrospiro[6H-2-benzothiopyran-6,2′-[1,3]dioxolane] (17) with N-phenylmaleimide. Reactions of 3-[2-(2-methyl-1,3-dioxolan-2-yl)ethyl]-4-[(tris(1-methylethyl)silyl)oxy]-2H-thiopyran (19) with maleimide, N-methylmaleimide, and N-phenylmaleimide under thermal conditions and with N-methylmaleimide, N-phenylmaleimide, 3-(propenoyl)-2-oxazolidinone, and methyl acrylate under Lewis acid mediated conditions (EtAlCl2, TiCl4) gave Diels–Alder adducts in moderate to good yields. In each case, those adducts were readily converted into products that are synthetically equivalent to Diels–Alder adducts of 17 with the same dienophiles. Desulfurization of those products gives 10-methyl-Δ4-octalins (2,3,4,4a,5,6,7,8-octahydro-4a-methylnapthalenes) that are synthetically equivalent to hypothetical Diels–Alder adducts of 1-ethenyl-2-methylcyclohexene-5-one. Keywords: Diels–Alder, 2H-thiopyran, cis-substituted 1,3-diene surrogate, 1-ethenyl-2-methylcyclohexene, octahydro-4a-methylnapthalene derivatives.

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42

Liu, Hsing-Jang, Wen-Lung Yeh, and Eric N. C. Browne. "Activated cycloheptenone dienophiles. A versatile approach to 6,7-fused ring targets." Canadian Journal of Chemistry 73, no. 7 (July 1, 1995): 1135–47. http://dx.doi.org/10.1139/v95-140.

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Several 2-carbalkoxy-2-cyclohepten-1-ones were prepared and their Diels–Alder characteristics examined in order to develop a facile general approach to the synthesis of cycloheptane ring-containing polycyclic natural products. Substitution pattern on the seven-membered ring was found to greatly affect the Diels–Alder behavior. In addition, some extraordinary facial stereoselectivity was observed. Keywords: Diels–Alder reaction, 2-carbalkoxy-2-cyclohepten-1-ones, 6,7-fused ring system.

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43

Marinier, Anne, Kurt Baettig, Carol Dallaire, Rita Pitteloud, and Pierre Deslongchamps. "Synthesis and transannular Diels–Alder reaction of a cis–trans–trans and a trans–cis–cis 13-membered macrocyclic trienone." Canadian Journal of Chemistry 67, no. 10 (October 1, 1989): 1609–17. http://dx.doi.org/10.1139/v89-246.

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The synthesis of the cis–trans–trans5 and trans–cis–cis6 macrocyclic trienones from cyclohexene is described. Upon heating at 300 °C, trienone 5 underwent 1,5-H shift and transannular Diels–Alder reaction to give adducts 33, 34, and 35 while trienone 6 provided tricyclic ketone 37. Keywords: transannular Diels–Alder reaction.

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44

Shimizu, Ryo, Yohei Okada, and Kazuhiro Chiba. "Stepwise radical cation Diels–Alder reaction via multiple pathways." Beilstein Journal of Organic Chemistry 14 (March 27, 2018): 704–8. http://dx.doi.org/10.3762/bjoc.14.59.

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Herein we disclose the radical cation Diels–Alder reaction of aryl vinyl ethers by electrocatalysis, which is triggered by an oxidative SET process. The reaction clearly proceeds in a stepwise fashion, which is a rare mechanism in this class. We also found that two distinctive pathways, including “direct” and “indirect”, are possible to construct the Diels–Alder adduct.

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45

Bueno, Maria P., Carlos Cativiela, José A. Mayoral, Alberto Avenoza, Paula Charro, Miguel A. Roy, and José M. Andres. "Natural amino acids as chiral auxiliaries in asymmetric Diels–Alder reactions." Canadian Journal of Chemistry 66, no. 11 (November 1, 1988): 2826–29. http://dx.doi.org/10.1139/v88-437.

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To test whether α-amino acids can be efficient chiral auxiliaries in asymmetric Diels–Alder reactions, the chiral dienophile N-acryloyl-L-phenylalanine methyl ester was made to react with cyclopentadiene. Diastereofacial selectivity is to a great extent dependent on the Lewis acid used to promote the reaction; whereas moderate excesses of the (1R,2R)-cycloadduct were achieved with AlCl3, the reaction did not show diastereofacial selectivity when titanium catalysts were used. Moreover, with Ti(iPrO)4 a transesterification reaction, which leads to the isopropyl ester and competes with the Diels–Alder reaction, was observed. In spite of the structural similarity of this dienophile to the acrylate of (S)-ethyl lactate, it behaved very differently in the titanium-catalyzed reactions.

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46

Pool, Brett, Rachel Goh, Jesse Roth-Barton, and Jonathan White. "Applying the Structure Correlation Principle to retro Diels Alder Reactions." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C923. http://dx.doi.org/10.1107/s2053273314090767.

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The early stages of molecular rearrangements are often apparent in the crystal structures of molecules susceptible to that rearrangement. For example, if a particular bond is broken, or if a particular group migrates during the rearrangement, then deviations of bond distances and angles from their `standard values' along the reaction coordinate are often observed. This is the structure correlation principle,1 which holds provided the molecule exists in the ground state, in a geometry, which is similar to the transition state geometry for the reaction. In this geometry the frontier orbitals whose interactions facilitate the reaction, can mix in the ground state. This paper discusses the application of this principle to pericyclic fragmentation reactions related to the retro Diels Alder reaction, using low temperature X-ray structural analysis of a range of model substrates. The substrates can be classified on the basis of this data into three groups: (i) those that undergo a synchronous retro Diels Alder reaction, (2) those that undergo an asynchronous retro Diels Alder reaction, and (3) those that react via a 2-step process. Examples of molecules falling into these three categories are given below.

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47

Rozek, Tomas, Wit Janowski, John M. Hevko, Edward R. T. Tiekink, Suresh Dua, David J. M. Stone, and John H. Bowie. "Syntheses of Angucyclinones Related to Ochromycinone." Australian Journal of Chemistry 51, no. 6 (1998): 515. http://dx.doi.org/10.1071/c97151.

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Two synthetic approaches have been investigated for the syntheses of model angucyclinones related to ochromycinone. The first involves a Diels–Alder/Friedel–Crafts strategy in which the Diels–Alder adduct formed between dimethyl acetylenedicarboxylate and 3-ethenyl-5,5-dimethylcyclohex-2-en-1- one was converted into 6,6-dimethyl-8-oxo-5,6,7,8-tetrahydronaphthalene-1,2-dicarboxylic anhydride, which was then reacted with benzene in a Friedel–Crafts reaction. Acid-catalysed cyclization of the Friedel–Crafts products gave 3,3-dimethyl-3,4-dihydrobenz[a]anthracene-1,7,12(2H)-trione (3) in poor yield. Angucyclinones related to (3) are formed (in 40–50% overall yield) by aromatization of the adduct formed between the appropriate 1,4-naphthoquinone and 3-[(E)-2-methoxyethenyl]- 5,5-dimethylcyclohex-2-en-1-one (this dienone reacts with itself by a Diels–Alder process to yield an adduct which decomposes to 3,3,8,8-tetramethyl-3,4,7,8-tetrahydroanthracene-1,6(2H,5H)-dione). When the substituted 1,4-naphthoquinone is unsymmetrical, a boron triacetate assisted Diels–Alder reaction gives a single regioisomer (e.g. X-ray investigations indicate that 8-hydroxy-3,3-dimethyl-3,4-dihydrobenz[a]anthracene-1,7,12(2H)-trione is the product from 5-hydroxy-1,4-naphthoquinone). An X-ray structural study of the Diels–Alder adduct in the above reaction confirms the operation of an endo cyclization.

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48

Ruiz-Pardo, Cinthya, Luisa Silva-Gutiérrez, Jaime Lizardi-Mendoza, Yolanda López-Franco, Carlos Peniche-Covas, and Waldo Argüelles-Monal. "Chitosan Hydrogels Based on the Diels–Alder Click Reaction: Rheological and Kinetic Study." Polymers 14, no. 6 (March 16, 2022): 1202. http://dx.doi.org/10.3390/polym14061202.

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The Diels–Alder reaction is recognized to generate highly selective and regiospecific cycloadducts. In this study, we carried out a rheological and kinetic study of N-furfuryl chitosan hydrogels based on the Diels–Alder click reaction with different poly(ethylene)glycol-maleimide derivatives in dilute aqueous acidic solutions. It was possible to prepare clear and transparent hydrogels with excellent mechanical properties. Applying the Winter and Chambon criterion the gel times were estimated at different temperatures, and the activation energy was calculated. The higher the temperature of gelation, the higher the reaction rate. The crosslinking density and the elastic properties seem to be controlled by the diffusion of the polymer segments, rather than by the kinetics of the reaction. An increase in the concentration of any of the two functional groups is accompanied by a higher crosslinking density regardless maleimide:furan molar ratio. The hydrogel showed an improvement in their mechanical properties as the temperature increases up to 70 °C. Above that, there is a drop in G’ values indicating that there is a process opposing to the Diels–Alder reaction, most likely the retro-Diels–Alder.

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49

Bachrach, Steven M., and Laureta M. Perriott. "Theoretical exammation of the Diels–Alder reaction of 1,3-butadiene with cyclopentadiene and 2H-phosphole." Canadian Journal of Chemistry 74, no. 6 (June 1, 1996): 839–50. http://dx.doi.org/10.1139/v96-093.

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All Diels–Alder reactions between 1,3-butadiene and cyclopentadiene or 2H-phosphole have been examined at the MP4SDQ/6-31G*//HF/6-31G* level. There is remarkable similarity between the two systems. The thermodynamic product is the bicyclo[4.2.0]nonadiene while the kinetic product is the norbornene product. There is a slight kinetic preference for the endo addition and for the butadiene to be in the s-trans conformation. Except for the case where butadiene is the diene component and addition is endo, the reactions are concerted and synchronous. In these other two cases, the reaction is stepwise with a diradical intermediate.Key words: phosphole, Diels–Alder reaction, topological electron density analysis.

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50

Spino, Claude, Laurel Clouston, and David Berg. "Novel, air-stable, lanthanide catalysts for the hetero Diels–Alder reaction." Canadian Journal of Chemistry 74, no. 9 (September 1, 1996): 1762–64. http://dx.doi.org/10.1139/v96-195.

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Novel, air-stable, yttrium and ytterbium complexes were found effective in the catalysis of the typical hetero Diels–Alder reaction of crotonaldehyde and ethylvinyl ether. They represent an attractive solution to the problem of ligand lability in the realm of lanthanide catalysts. Key words: lanthanide, catalyst, hetero Diels–Alder, yttrium, ytterbium.

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