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Journal articles on the topic 'Endo-exo selectivity'

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Published: 10 December 2022
Last updated: 28 January 2023

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1

Ward, Dale E., and Yuanzhu Gai. "Lewis acid mediated Diels–Alder reactions of 2H-thiopyrans." Canadian Journal of Chemistry 70, no. 10 (October 1, 1992): 2627–34. http://dx.doi.org/10.1139/v92-331.

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Lewis acid mediated Diels–Alder reactions of 2H-thiopyrans with acrylate, crotonate, and methacrylate dienophiles have been investigated. Modest to good yields of predominantly exo adducts are obtained with 4-substituted 2H-thiopyrans. With 5-substituted 2H-thiopyrans, high endo selectivity is observed. No adducts were produced with methacrylate dienophiles. Relative to the thermal reactions, the exo selectivity is enhanced in the presence of Lewis acids. Unusually high exo selectivity is observed using "wet" Et2AlCl as the promoter.
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2

Shivanyuk, Alexander, Andrii Gerasov, Rodion Boiko, Grygoriy Dolgonos, Aleksandr Mandzhulo, Volodymyr Fetyukhin, and Oleg Lukin. "Tropane-Based Dispirocyclic Oxiranes and Spirocyclic Ketones." Synthesis 54, no. 03 (December 6, 2021): 723–31. http://dx.doi.org/10.1055/s-0040-1719848.

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AbstractThe Prilezhaev epoxidation of N-Boc-protected 3-cyclobutylidenetropane 1a affords a 1:2 mixture of compounds 2a and 2b, in which tropane and cyclobutane fragments are spiro-connected to the oxirane ring in endo- and exo-fashion, respectively. The exo-isomer 2b is obtained in 89% yield and 97% selectivity via the dioxirane oxidation of 1a. BF3-catalyzed isomerization of exo-oxirane 2b results in a 1:1 mixture of the spirocyclic ketones endo 3a and exo 3b containing spiro-connected tropane and cyclopentanone rings, while endo-epoxide 2a gives exclusively endo-ketone 3a. Prilezhaev and dioxirane epoxidations of N-Boc-protected 3-cyclopropylidenetropane 1b affords a mixture of endo- and exo-oxiranes 2c and 2d. Compounds 2c and 2d are not isolated in individual forms since they isomerize into a mixture of spirocyclic ketones endo 3c and exo 3d. Removal of the Boc groups from ketones 3a–d gives the corresponding hydrochlorides of aminoketones 4a–d in quantitative yields. Quantum chemical calculations predict that the rearrangement of endo-epoxides into the corresponding endo-ketones involving BF3-containing intermediates has by 4.4–7.9 kcal/mol lower activation barriers than the respective conversion of the exo-epoxides into exo-ketones. The cyclopropyl-containing dispiroepoxides 2c and 2d are predicted to interconvert faster into the corresponding ketones compared to their less strained cyclobutyl counterparts 2a and 2b.
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3

Okuda, Yasuhiro, Robert K. Szilagyi, Seiji Mori, and Yasushi Nishihara. "The origin of exo-selectivity in methyl cyanoformate addition onto the CC bond of norbornene in Pd-catalyzed cyanoesterification." Dalton Trans. 43, no. 25 (2014): 9537–48. http://dx.doi.org/10.1039/c4dt00839a.

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The origin of exclusive exo-selectivity in the Pd-catalyzed cyanoesterification reaction of methyl cyanoformate is attributed to the decisive energy gap between the exo- and endo-coordination of norbornene to the PdII 14-electron, coordinatively unsaturated complex.
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4

Infante, Genesis, and Sara Eisler. "Accessing pyrrolones and pyridinones: controlling 5-exo and 6-endo ring closures in heterocyclic alkynylamides." Canadian Journal of Chemistry 95, no. 4 (April 2017): 415–23. http://dx.doi.org/10.1139/cjc-2016-0524.

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Competitive 5-exo and 6-endo anionic intramolecular cyclization reactions in heterocyclic alkynylamides were explored via experimental and computational analysis. The 5-exo-dig cyclization pathway is usually disfavoured in heterocyclic systems, and 6-endo products are often both the kinetic and thermodynamic products. However, we’ve found that it is possible to shift selectivity toward the 5-exo-dig pyrrolone products away from the less strained pyridinone products that are produced via the 6-endo-dig cyclization. Parameters such as identity of heteroatom, heteroatom positioning within the heterocycle, and functionality on the alkyne were investigated and, in many cases, were found to strongly influence product ratios. A series of computational studies was performed to provide further insight into the 5-exo-dig and 6-endo-dig pathways in these heterocyclic systems. Theoretical predictions were found to reproduce experimental results, highlighting the predictive capabilities of the computations in determining preferred products.
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5

Legnani, Laura, Salvatore V. Giofré, Daniela Iannazzo, Consuelo Celesti, Lucia Veltri, and Maria Assunta Chiacchio. "Chemoselective Oxidation of Isoxazolidines with Ruthenium Tetroxide: A Successful Intertwining of Combined Theoretical and Experimental Data." Molecules 27, no. 17 (August 24, 2022): 5390. http://dx.doi.org/10.3390/molecules27175390.

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The direct oxidation reaction of isoxazolidines plays an important role in organic chemistry, leading to the synthesis of biologically active compounds. In this paper, we report a computational mechanistic study of RuO4-catalyzed oxidation of differently N-substituted isoxazolidines 1a–c. Attention was focused on the endo/exo oxidation selectivity. For all the investigated compounds, the exo attack is preferred to the endo one, showing exo percentages growing in parallel with the stability order of transient carbocations found along the reaction pathway. The study has been supported by experimental data that nicely confirm the modeling results.
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6

Tamilmani, V., C. A. Daul, and P. Venuvanalingam. "Electrostatic control on endo/exo selectivity in ionic cycloaddition." Chemical Physics Letters 416, no. 4-6 (December 2005): 354–57. http://dx.doi.org/10.1016/j.cplett.2005.09.120.

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7

Solans-Monfort, Xavier. "DFT study on the reaction mechanism of the ring closing enyne metathesis (RCEYM) catalyzed by molybdenum alkylidene complexes." Dalton Trans. 43, no. 11 (2014): 4573–86. http://dx.doi.org/10.1039/c3dt53242a.

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8

İşleyen, Alper, Tuğmac Sayraç, and Özdemir Doğan. "Boron Trifluoride Mediated Addition of Nucleophiles to endo- and exo-Substituted Norbornene Derivatives." Zeitschrift für Naturforschung B 59, no. 1 (January 1, 2004): 109–18. http://dx.doi.org/10.1515/znb-2004-0116.

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Abstract Remote substituent effects on the regioselectivity and stereoselectivity in the boron trifluoride mediated addition of nucleophiles (iodide and bromide) to endo- and exo-2-substituted norbornene derivatives have been investigated. The main products of the reactions resulted from the regioselective addition of nucleophiles to the double bond of norbornene derivatives. Products resulting from the Wagner-Meerwein type rearrangement were also isolated in considerable amounts. All of the reactions gave the addition products in reasonably good yields with high regioselectivity. The endo/exo selectivity, on the other hand, changed depending on the nucleophile and the substrate.
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9

Gerasov, Andrii, Grygoriy A. Dolgonos, Aleksandr Yu Mandzhulo, Alexey Ryabitsky, Volodymyr Fetyukhin, Oleg Lukin, and Alexander Shivanyuk. "Selective Synthesis of exo-Spiro[2′,2′-difluorocyclopropane-3′,2′-tropanes]." Synthesis 52, no. 07 (January 2, 2020): 1015–24. http://dx.doi.org/10.1055/s-0039-1691560.

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Conformationally restrained exo-isomers of N-Boc-protected spiro[2′,2′-difluorocyclopropane-3′,2′-tropanes] were synthesized in 62–83% yield via absolutely diastereoselective cycloaddition of CF2, generated in situ from Me3SiCF3/NaI in refluxing THF, to double bonds of 3-alkylidenetropanes. Standard removal of Boc protecting groups afforded corresponding exo-spiro[2′,2′-difluorocyclopropane-3′,2′-tropane] hydrochlorides in 82–94% yields. DFT and CCSD(T) calculations revealed that the observed exo-selectivity of difluorocarbene addition is likely to be caused by a lower activation barrier of the exo-difluorocyclopropanation compared to the endo-reaction.
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10

Gosse, Tammy L., and Raymond A. Poirier. "Exo selectivity and the effect of disubstitution in the Diels–Alder reactions of butadiene with 3,3-disubstituted cyclopropenes." Canadian Journal of Chemistry 82, no. 11 (November 1, 2004): 1589–96. http://dx.doi.org/10.1139/v04-115.

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A density functional computational study was performed to accomplish two tasks: to examine the endo–exo selectivity in the Diels–Alder reactions of 3,3-disubstituted cyclopropenes with s-cis-butadiene, and to study the effect of disubstitution on the reactivity of the cyclopropene dienophile. Cyclopropene is substituted at C-3 with CH3, SiH3, NH2, PH2, OH, SH, F, and Cl; both 3-substituted and 3,3-disubstituted ground states are examined to determine relative reactivities. The exo transition-state structures are consistently lower in energy than the endo transition-state structures for the 3,3-disubstituted cyclopropene – butadiene system, and surprisingly, both modes of addition have lower activation barriers than the syn 3-substituted cyclopropene – butadiene system. Through a series of isodesmic reactions, we have concluded that there is an additional stabilization in the transition-state structures of the 3,3-disubstituted system that can account for the lowering of the activation barriers below that of the 3-substituted cases. This stabilization is a combination of the anomeric effect and the ring relaxation that occurs in the transition-state structure.Key words: Diels–Alder reaction, cyclopropene, exo selectivity, anomeric effect.
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11

Fišera, Lubor, Vladimír Oremus, Ladislav Štibrányi, Hans-Joachim Timpe, and Alena Máťušová. "Photo-induced rearrangement of isoxazolines - A pathway to 2,4,5,8-tetrahydro-1,3-dioxa-5-azocine derivatives." Collection of Czechoslovak Chemical Communications 50, no. 9 (1985): 1982–93. http://dx.doi.org/10.1135/cccc19851982.

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4-R-Substituted-8-X-phenyl-3,5,10-trioxa-9-azabicyclo[3,5,0]dec-8-enes (X = H, 4-CH3, 4-OCH3, 4-Cl, 4-Br, 4-F, 3-NO2, 3-Cl, 3-Br) have been prepared by cycloaddition of substituted benzenenitriloxides with 2-R-substituted 1,3-dioxep-5-enes (R = H, CH3, C6H5). A mixture of the endo and exo adducts is formed, if R is CH3 or C6H5. Their irradiation produces high yields of the title compounds as the single products. High selectivity of the photo-rearrangement is due to resonance stabilization of the biradical with p electrons of the oxygen atom. The quantum yields of the photoreaction vary from 0.02 to 0.04 depending on the substituent X. An unexpected dependence has been found between the quantum yield of the photo-rearrangement and stereochemical arrangement of the 4-R-substituent: exo derivatives exhibit higher values than the endo derivatives. Also different are UV spectra of the endo and exo derivatives. A new synthesis principle is described enabling preparation of (n + 1)-membered heterocycles from n-membered heterocycles.
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12

Minuti, Lucio, Roberta Selvaggi, Aldo Taticchi, Ming Guo, and Ernest Wenkert. "Diels–Alder reactions of bicyclic, heteroannular dienones." Canadian Journal of Chemistry 70, no. 5 (May 1, 1992): 1481–85. http://dx.doi.org/10.1139/v92-183.

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Aluminum chloride catalyzed Diels–Alder reactions of bicyclic dienones of the hexalone type with 1,3-butadiene, isoprene, (E)-piperylene, and (E)-1-methoxy-1,3-butadiene are described. Structure analysis of the adducts by NMR spectroscopy is presented. The site-, endo–exo-, and face-selectivity of the reactions are discussed.
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13

Yan, Shihai, Do-Hyun Ryu, and Jin-Yong Lee. "Origin of Exo/Endo Selectivity in the Intramolecular Diels-Alder Reaction." Bulletin of the Korean Chemical Society 31, no. 9 (September 20, 2010): 2527–30. http://dx.doi.org/10.5012/bkcs.2010.31.9.2527.

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14

Batllori, Rosa, Josep Font, Montserrat Monsalvatje, Rosa M. Ortuño, and Francisco Sanchez-Ferrando. "Diels-alder cycloadditions of chiral butenolides with cyclopentadiene: endo/exo selectivity." Tetrahedron 45, no. 6 (January 1989): 1833–38. http://dx.doi.org/10.1016/s0040-4020(01)80048-x.

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15

Velez, Caroline, Brian Doherty, and Orlando Acevedo. "Accurate Diels-Alder Energies and Endo Selectivity in Ionic Liquids Using the OPLS-VSIL Force Field." International Journal of Molecular Sciences 21, no. 4 (February 11, 2020): 1190. http://dx.doi.org/10.3390/ijms21041190.

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Our recently developed optimized potentials for liquid simulations-virtual site ionic liquid (OPLS-VSIL) force field has been shown to provide accurate bulk phase properties and local ion-ion interactions for a wide variety of imidazolium-based ionic liquids. The force field features a virtual site that offloads negative charge to inside the plane of the ring with careful attention given to hydrogen bonding interactions. In this study, the Diels-Alder reaction between cyclopentadiene and methyl acrylate was computationally investigated in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], as a basis for the validation of the OPLS-VSIL to properly reproduce a reaction medium environment. Mixed ab initio quantum mechanics and molecular mechanics (QM/MM) calculations coupled to free energy perturbation and Monte Carlo sampling (FEP/MC) that utilized M06-2X/6-31G(d) and OPLS-VSIL gave activation free energy barriers of 14.9 and 16.0 kcal/mol for the endo-cis and exo-cis Diels-Alder reaction pathways, respectively (exptl. ΔH‡ of 14.6 kcal/mol). The endo selectivity trend was correctly predicted with a calculated 73% endo preference. The rate and selectivity enhancements present in the endo conformation were found to arise from preferential hydrogen bonding with the exposed C4 ring hydrogen on the BMIM cation. Weaker electronic stabilization of the exo transition state was predicted. For comparison, our earlier ±0.8 charge-scaled OPLS-2009IL force field also yielded a ΔG‡ of 14.9 kcal/mol for the favorable endo reaction pathway but did not adequately capture the highly organized solvent interactions present between the cation and Diels-Alder transition state.
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16

Suárez, D., and J. A. Sordo. "On the origin of the endo/exo selectivity in Diels–Alder reactions." Chemical Communications, no. 3 (1998): 385–86. http://dx.doi.org/10.1039/a707086a.

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17

Wałejko, Piotr, Michał Dąbrowski, Lech Szczepaniak, Jacek W. Morzycki, and Stanisław Witkowski. "Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate." Beilstein Journal of Organic Chemistry 11 (October 13, 2015): 1893–901. http://dx.doi.org/10.3762/bjoc.11.204.

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The ROCM reactions of exo- and endo-2-cyano-7-oxanorbornenes with allyl alcohol or allyl acetate promoted by different ruthenium alkylidene catalysts were studied. The stereochemical outcome of the reactions was established. The issues concerning chemo- (ROCM vs ROMP), regio- (1-2- vs 1-3-product formation), and stereo- (E/Z isomerism) selectivity of reactions under various conditions are discussed. Surprisingly good yields of the ROCM products were obtained under neat conditions.
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18

Cainelli, Gianfranco, Paola Galletti, Daria Giacomini, and Arianna Quintavalla. "Dynamic solvation effects on the endo/exo selectivity of the Diels–Alder reaction." Tetrahedron Letters 44, no. 1 (January 2003): 93–96. http://dx.doi.org/10.1016/s0040-4039(02)02477-2.

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19

Zimmerman, Howard E., and Linus W. Linder. "Enhanced endo-exo selectivity in the stereochemistry of ketonization of enols. Part 201." Journal of Organic Chemistry 50, no. 10 (May 1985): 1637–46. http://dx.doi.org/10.1021/jo00210a016.

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20

Sustmann, Reiner, Willi Sicking, Hélène Lamy-Schelkens, and Léon Ghosez. "endo/exo selectivity in cycloadditions of 2,6-bis-silyloxy-3,4-dihydropyridine with methylacrylate." Tetrahedron Letters 32, no. 11 (March 1991): 1401–4. http://dx.doi.org/10.1016/0040-4039(91)80341-3.

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21

Merouani, Hafida, Christophe Morell, Nadia Ouddai, and Henry Chermette. "DFT study of the stereo-selectivity of oxygenated heterocycles from 10 to 12 links." Canadian Journal of Chemistry 91, no. 9 (September 2013): 811–20. http://dx.doi.org/10.1139/cjc-2012-0521.

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Intra-molecular Diels–Alder (IMDA) reactions of tethered trienes can furnish two distinct diastereoisomeric products, the cis (i.e., endo) stereoisomer and the trans (i.e., exo) stereoisomer. Experimental evidence shows a quite high cis stereo-selectivity for 10-link compounds (cis/trans = 70:30), while 11- and 12-links compounds exhibit no particular selectivity. DFT (B3LYP/6-31G*) computations provide useful insights into the origins of this amazing stereo-selectivity. The cyclization path towards trans stereo-isomer is always thermodynamically favored, whatever the size of the system. The high cis stereo-selectivity displayed by the 10-link system is kinetically controlled by a tug-of-war between ring strain and electronic effects in the transition structure. The dual descriptor of chemical reactivity, a conceptual DFT based descriptor designed to delineate electronic effects, has been used to unravel the stabilizing processes that take place at the TSs.
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22

Werstiuk, Nick Henry, and Chandra Deo Roy. "Experimental and AM1 calculational studies of the deprotonation of bicyclo[2.2.2]octane-2,5-dione and bicyclo[2.2.2]octane-2,6-dione: a study of homoconjugation, inductive, and steric effects on the rates and diastereoselectivities of α enolization." Canadian Journal of Chemistry 73, no. 3 (March 1, 1995): 460–63. http://dx.doi.org/10.1139/v95-060.

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The kinetics of NaOD-catalyzed H/D exchange (enolization) at C3 α to the carbonyl group of bicyclo[2.2.2]octane-2,5-dione (1) and bicyclo[2.2.2]octane-2,6-dione (2) have been studied in 60:40 (v/v) dioxane–D2O at 25.0 °C. The second-order rate constants for exchange are (9.7 ± 1.5) × 10−1 and (3.4 ± 1.2) × 10−5 L mol−1 s−1 for 1 and 2, respectively. Thus, 1, exchanges 76 times faster than bicyclo[2.2.2]octan-2-one (3) (k = (1.27 ± 0.02) × 10−2 L mol−1 s−1), but the 2,6-dione 2 unexpectedly is much less reactive (2.7 × 10−3) than the monoketone. Unlike the large exo selectivity of 658 observed in the case of bicyclo[2.2.1]heptan-2-one, small and opposite selectivities, exo (1.2) for 1 and endo (2.1) for 2, are found for the isomeric [2.2.2] ketones. The results indicate that the incipient enolate of 1 is stabilized by a polar effect of the β carbonyl group at C5, not by homoconjugation. The source of the surprising low reactivity of 2 is unknown at this stage. The small diastereoselectivities, exo (1.2) for 1 and endo (2.1) for 2, correlate with relative energies of the diastereomeric pyramidal enolates calculated with AM1. Keywords: enolization, bicyclo[2.2.2]octane-2,5-dione, bicyclo[2.2.2]octane-2,6-dione, AM1, thermodynamic acidities.
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23

Schwarz, Joseph, and Helmut Schwarz. "exo/endo-Selectivity in the Reaction of ?Bare? FeO+ with Bicyclo[2.2.1]heptane (Norbornane)." Helvetica Chimica Acta 78, no. 4 (June 28, 1995): 1013–19. http://dx.doi.org/10.1002/hlca.19950780423.

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24

Meir, Rinat, Hui Chen, Wenzhen Lai, and Sason Shaik. "Corrigendum: Oriented Electric Fields Accelerate Diels–Alder Reactions and Control the endo / exo Selectivity." ChemPhysChem 21, no. 15 (August 4, 2020): 1737. http://dx.doi.org/10.1002/cphc.201900495.

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25

SUSTMANN, R., W. SICKING, H. LAMY-SCHELKENS, and L. GHOSEZ. "ChemInform Abstract: endo/exo-Selectivity in Cycloadditions of 2,6-Bissilyloxy-3,4- dihydropyridine with Methylacrylate." ChemInform 23, no. 2 (August 22, 2010): no. http://dx.doi.org/10.1002/chin.199202085.

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26

Hooper, Joel F., Jonathan M. White, and Andrew B. Holmes. "Development of the Claisen Rearrangement/Organocatalytic Diels-Alder Approach for the Synthesis of Eunicellins." Australian Journal of Chemistry 67, no. 9 (2014): 1189. http://dx.doi.org/10.1071/ch14030.

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The intramolecular Diels-Alder approach to synthesizing eunicellins has proved to be a powerful method for the synthesis of this class of natural products. The key to the success of this strategy is control over the endo/exo selectivity of the cycloaddition reaction, which we have addressed through an organocatalytic reaction employing the MacMillan imidazolidinone catalyst. This approach has been further developed to address the issue of functionality at the C8 position, and a novel scalable method for the extension of the medium-ring lactone has been developed.
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27

Šmit, Biljana M., Radoslav Z. Pavlović, Dejan A. Milenković, and Zoran S. Marković. "Mechanism, kinetics and selectivity of selenocyclization of 5-alkenylhydantoins: an experimental and computational study." Beilstein Journal of Organic Chemistry 11 (October 7, 2015): 1865–75. http://dx.doi.org/10.3762/bjoc.11.200.

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The mechanism and selectivity of a bicyclic hydantoin formation by selenium-induced cyclization are investigated. The proposed mechanism involves the intermediates formed by an electrophilic addition of the selenium reagent on a double bond of the starting 5-alkenylhydantoin prior the cyclization. These intermediates are readily converted into the more stable cyclic seleniranium cations. A key step of the mechanism is an intramolecular cyclization which is realized through an anti-attack of the internal nucleophile, the amidic nitrogen, to the seleniranium cation yielding the intermediate imidazolinium cations. Their deprotonation is followed by the formation of the fused bicyclic reaction products. Important intermediates and key transition states are studied by using density functional theory (DFT) methods. The pathways of the reaction are investigated in detail. There are two regioselective pathways related to 5-exo and 6-endo products. Theoretical calculations and the monitoring of the cyclization reaction using 1H NMR spectroscopy are in a good agreement with the proposed mechanism and are consistent with our experimental results. The preferred pathway for formation of 5-exo products is confirmed.
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28

Parvez, M., A. Rauk, T. S. Sorensen, and F. Sun. "Structure reassignment of the major isomer from the Diels-Alder reaction of acryloyl chloride and 4,5,6,6a-tetrahydropentalene." Canadian Journal of Chemistry 76, no. 9 (September 1, 1998): 1289–93. http://dx.doi.org/10.1139/v98-168.

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After hydrogenation and hydrolysis, the two adducts formed from the Diels-Alder reaction of acryloyl chloride and 4,5,6,6a-tetrahydropentalene were originally assigned 7-exo- and 7-endo-carboxylic acid structures 3 and 4. Based on unexpected results in using these acids as starting materials for a superacid carbocation study, a reinvestigation of these structural assignments was carried out. From an extensive series of 2D NMR experiments, we conclude that 4 is correctly assigned, but that the other isomer is the 9-endo carboxylic acid 8. The formation of these two isomers (out of eight possible modes of addition) can be rationalized. Finally, an X-ray study of 8 was carried out as a final proof of structure.Key words: Diels-Alder reaction, facial selectivity, regioselectivity, X-ray structure, MO calculation.
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29

McCleary, Barry V., Lucie M. J. Charmier, Vincent A. McKie, Ciara McLoughlin, and Artur Rogowski. "Determination of Fructan (Inulin, FOS, Levan, and Branched Fructan) in Animal Food (Animal Feed, Pet Food, and Ingredients): Single-Laboratory Validation, First Action 2018.07." Journal of AOAC INTERNATIONAL 102, no. 3 (May 1, 2019): 883–92. http://dx.doi.org/10.5740/jaoacint.18-0330.

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Abstract Traditional enzyme-based methods for measurement of fructan were designed to measure just inulin and branched-type (agave) fructans. The enzymes employed, namely exo-inulinase and endo-inulinase, give incompletely hydrolysis of levan. Levan hydrolysis requires a third enzyme, endo-levanase. This paper describes a method and commercial test kit (Megazyme Fructan Assay Kit) for the determination of all types of fructan (inulin, levan, and branched) in a variety of animal feeds and pet foods. The method has been validated in a single laboratory for analysis of pure inulin, agave fructan, levan, and a range of fructan containing samples. Quantification is based on complete hydrolysis of fructan to fructose and glucose by a mixture of exo-inulinase, endo-inulinase, and endo-levanase, followed by measurement of these sugars using the PAHBAH reducing sugar method which gives the same color response with fructose and glucose. Before hydrolysis of fructan, interfering sucrose and starch in the sample are specifically hydrolyzed and removed by borohydride reduction. The single-laboratory validation (SLV) outlined in this document was performed on commercially available inulin (Raftiline) and agave fructan (Frutafit®), levan purified from Timothy grass, two grass samples, a sample of legume hay, two animal feeds and two barley flours, one of which (Barley MAX®) was genetically enriched in fructan through plant breeding. Parameters examined during the validation included working range, target selectivity, recovery, LOD, LOQ, trueness (bias), precision (repeatability and intermediate precision), robustness, and stability. The method is robust, quick, and simple.
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30

Sato, Michio, Shinji Kishimoto, Mamoru Yokoyama, Cooper S. Jamieson, Kazuto Narita, Naoya Maeda, Kodai Hara, et al. "Catalytic mechanism and endo-to-exo selectivity reversion of an octalin-forming natural Diels–Alderase." Nature Catalysis 4, no. 3 (March 2021): 223–32. http://dx.doi.org/10.1038/s41929-021-00577-2.

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31

Niwayama, Satomi, Hanjoung Cho, Masoud Zabet-Moghaddam, and Bruce R. Whittlesey. "Remote Exo/Endo Selectivity in Selective Monohydrolysis of Dialkyl Bicyclo[2.2.1]heptane-2,3-dicarboxylate Derivatives." Journal of Organic Chemistry 75, no. 11 (June 4, 2010): 3775–80. http://dx.doi.org/10.1021/jo100564e.

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32

Ha, Jae Du, Chul Hyun Kang, Kenneth A. Belmore, and Jin Kun Cha. "Diels−Alder Reactions of 2-(N-Acylamino)-1,3-dienes. Atypical Regioselectivity and Endo/Exo Selectivity." Journal of Organic Chemistry 63, no. 12 (June 1998): 3810–11. http://dx.doi.org/10.1021/jo980593k.

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33

Keseru, G. "Theoretical study on the 5-exo/6-endo selectivity in the cyclization of electrophilic radicals." Journal of Molecular Structure: THEOCHEM 392, no. 1 (March 31, 1997): 95–99. http://dx.doi.org/10.1016/s0166-1280(96)04870-1.

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34

Keseru , György M., László To ke, Zoltán Hell, Zsuzsanna M. Jászay, Imre Petneházy, and László Korecz. "Theoretical study on the 5-exo/6-endo selectivity in the cyclization of electrophilic radicals." Journal of Molecular Structure: THEOCHEM 392 (March 1997): 95–99. http://dx.doi.org/10.1016/s0166-1280(97)90381-x.

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35

Hooper, Joel F., Natalie C. James, Esra Bozkurt, Viktorya Aviyente, Jonathan M. White, Mareike C. Holland, Ryan Gilmour, Andrew B. Holmes, and K. N. Houk. "Medium-Ring Effects on the Endo/Exo Selectivity of the Organocatalytic Intramolecular Diels–Alder Reaction." Journal of Organic Chemistry 80, no. 24 (November 30, 2015): 12058–75. http://dx.doi.org/10.1021/acs.joc.5b02037.

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36

Alonzo, Daniel, Vicen¢ Branchadell, Josep Font, Antonio Oliva, Rosa M. Ortuño, and Francisco Sánchez-Ferrando. "5-Methylene-2(5H)-furanone in Diels-Alder reactions with cyclic dienes: endo/exo selectivity." Tetrahedron 46, no. 12 (1990): 4371–78. http://dx.doi.org/10.1016/s0040-4020(01)86771-5.

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37

Larrañaga, Olatz, and Abel de Cózar. "Effect of an α-Methyl Substituent on the Dienophile on Diels-Alder endo :exo Selectivity." ChemistryOpen 8, no. 1 (January 2019): 49–57. http://dx.doi.org/10.1002/open.201800237.

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38

Barešić, Luka, Davor Margetić, and Zoran Glasovac. "Cycloaddition of Thiourea- and Guanidine-Substituted Furans to Dienophiles: A Comparison of the Environmentally-Friendly Methods." Chemistry Proceedings 3, no. 1 (November 14, 2020): 57. http://dx.doi.org/10.3390/ecsoc-24-08380.

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The cycloaddition strategy was employed in order to obtain a 7-oxanorbornene framework substituted with a guanidine moiety or its precursor functional groups: protected amine or thiourea. In order to optimize the conditions for the cycloaddition, several environmentally-friendly methods—microwave assisted organic synthesis, high pressure synthesis, high speed vibrational milling, and ultrasound assisted synthesis—were employed. The outcomes of the cycloaddition reactions were interpreted in terms of endo/exo selectivity, the conversion of the reactants to the product, and the isolated yields. In general, our results indicated the HP and HSVM approaches as the methods of choice to give good yields and conversions.
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39

Niwayama, Satomi, and Yoshikazu Hiraga. "New exo/endo selectivity observed in monohydrolysis of dialkyl bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylates." Tetrahedron Letters 44, no. 47 (November 2003): 8567–70. http://dx.doi.org/10.1016/j.tetlet.2003.09.131.

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40

Yates, Peter, Anabela Gomes, D. Jean Burnell, Dong Dao Cong, and Jeffery F. Sawyer. "Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Diels–Alder reactions with dimethyl acetylenedicarboxylate." Canadian Journal of Chemistry 67, no. 1 (January 1, 1989): 37–47. http://dx.doi.org/10.1139/v89-007.

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6,6-Disubstituted 2,4-cyclohexadien-1-ones can be prepared by dibromination–bisdehydrobromination of the corresponding 6,6-disubstituted 2,2-dibromocyclohexanones. Such dienes undergo Diels–Alder reactions with dimethyl acetylenedicarboxylate to give 3,3-disubstituted 5,6-di(methoxycarbonyl)bicyclo[2.2.2]octa-5,7-dien-2-ones; when the substituents at C-6 in the dienones are different, two diastereomers of the adducts are formed in a ratio dependent on the "facial selectivity" in the Diels–Alder reactions. For the cases where one of the 6-substituents is methyl and the other is methoxycarbonyl, acetoxymethyl, dibromomethyl, or dichloromethyl it has been established via X-ray crystallography and chemical correlation that the endo-3-methyl/exo-3-methyl product ratio is 3.0, 0.9, 8, and 6, respectively. The origin of these differences is discussed briefly and a spectroscopic method for the assignment of structures to the individual diastereomers is proposed. Keywords: Diels–Alderreactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.
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41

Lang, Yanmin, Mei Zhang, Yang Cao, and Genping Huang. "Mechanism and origins of the directing group-controlled endo- versus exo-selectivity of iridium-catalysed intramolecular hydroalkenylation of 1,1-disubstituted alkenes." Chemical Communications 54, no. 21 (2018): 2678–81. http://dx.doi.org/10.1039/c8cc00074c.

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42

Li, Zhenghua, Amit Kumar, Sunil K. Sharma, Virinder S. Parmar, and Erik V. Van der Eycken. "Catalyst-controlled exo/endo selectivity in a post-Ugi intramolecular hydroarylation: synthesis of pyrrolopyridinones, pyrroloazepinones, and benzothienopyridines." Tetrahedron 71, no. 21 (May 2015): 3333–42. http://dx.doi.org/10.1016/j.tet.2015.03.103.

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43

Sodupe, Mariona, Raphael Rios, Vicenç Branchadell, Tony Nicholas, Antonio Oliva, and J. J. Dannenberg. "A Theoretical Study of the Endo/Exo Selectivity of the Diels−Alder Reaction between Cyclopropene and Butadiene." Journal of the American Chemical Society 119, no. 18 (May 1997): 4232–38. http://dx.doi.org/10.1021/ja9628260.

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44

HA, J. D., C. H. KANG, K. A. BELMORE, and J. K. CHA. "ChemInform Abstract: Diels-Alder Reactions of 2-(N-Acylamino)-1,3-dienes. Atypical Regioselectivity and endo/exo Selectivity." ChemInform 29, no. 45 (June 19, 2010): no. http://dx.doi.org/10.1002/chin.199845155.

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45

Penín, Lucía, Matteo Gigli, Federica Sabuzi, Valentín Santos, Pierluca Galloni, Valeria Conte, Juan Carlos Parajó, Heiko Lange, and Claudia Crestini. "Biomimetic Vanadate and Molybdate Systems for Oxidative Upgrading of Iono- and Organosolv Hard- and Softwood Lignins." Processes 8, no. 9 (September 16, 2020): 1161. http://dx.doi.org/10.3390/pr8091161.

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Recently reported acetosolv soft- and hardwood lignins as well as ionosolv soft- and hardwood lignins were transformed into monomeric aromatic compounds using either a vanadate or a molybdate-based catalyst system. Monomers were generated with remarkable, catalyst-dependent selectivity and high depolymerisation yields via oxidative exo- and endo-depolymerisation processes. Using the vanadate–hydrogen peroxide system on acetosolv pine lignin, vanillin and isovanillin were produced as main products with depolymerisation yields of 31%. Using the molybdate system on acetosolv and ionosolv lignin, vanillic acid was the practically exclusive product, with depolymerisation yields of up to 72%. Similar selectivities, albeit with lower depolymerisation yields of around 50% under standardised conditions, were obtained for eucalyptus acetosolv lignin, producing vanillin and syringaldehyde or vanillic acid as products, by using the vanadate- or the molybdate-based systems respectively.
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46

Schlachter, Ingo, Jochen Mattay, Josef Suer, Udo Höweler, Gudrun Würthwein, and Ernst-Ulrich Würthwein. "Combined quantum chemical and MM-approach to the endo/exo selectivity of diels-alder reactions in polar media." Tetrahedron 53, no. 1 (January 1997): 119–32. http://dx.doi.org/10.1016/s0040-4020(96)00957-x.

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47

Di Valentin, Cristiana, Mauro Freccero, Mirko Sarzi-Amadè, and Riccardo Zanaletti. "Reactivity and endo–exo Selectivity in Diels–Alder Reaction of o-Quinodimethanes. An Experimental and DFT Computational Study." Tetrahedron 56, no. 16 (April 2000): 2547–59. http://dx.doi.org/10.1016/s0040-4020(00)00126-5.

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48

Takeda, Kei, Ikuhiro Imaoka, and Eiichi Yoshii. "Diels-Alder reaction of α-substituted acrylates and α-(methylene)lactones: Conformation of dienophiles and endo/exo selectivity." Tetrahedron 50, no. 37 (January 1994): 10839–48. http://dx.doi.org/10.1016/s0040-4020(01)85696-9.

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49

Ma, Mengtao, Ruifeng Lu, Sumod A. Pullarkat, Weiqiao Deng, and Pak-Hing Leung. "Steric effects on the control of endo/exo-selectivity in the asymmetric cycloaddition reaction of 3,4-dimethyl-1-phenylarsole." Dalton Transactions 39, no. 23 (2010): 5453. http://dx.doi.org/10.1039/b924613d.

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50

Li, Zhenghua, Amit Kumar, Sunil K. Sharma, Virinder S. Parmar, and Erik V. Van der Eycken. "ChemInform Abstract: Catalyst-Controlled exo/endo Selectivity in a Post-Ugi Intramolecular Hydroarylation: Synthesis of Pyrrolopyridinones, Pyrroloazepinones, and Benzothienopyridines." ChemInform 46, no. 37 (August 27, 2015): no. http://dx.doi.org/10.1002/chin.201537035.

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