Готові списки джерел за темами / Endo-exo selectivity

Добірка наукової літератури з теми "Endo-exo selectivity"

Автор: Grafiati
Опубліковано: 10 грудня 2022
Оновлено: 28 січня 2023

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Статті в журналах з теми "Endo-exo selectivity"

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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Анотація:
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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Анотація:
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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Анотація:
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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Анотація:
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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Анотація:
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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Анотація:
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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Анотація:
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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Більше джерел

Дисертації з теми "Endo-exo selectivity"

1

Lording, William James. "A deeper understanding of the Diels–Alder reaction." Phd thesis, 2010. http://hdl.handle.net/1885/11776.

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Анотація:
The Diels-Alder reaction was discovered in 1928 and has become the most efficient and practical method for the synthesis of six-membered carbocyclic and heterocyclic rings. This thesis comprises three chapters of results and discussion with the Diels-Alder reaction as a theme. Chapter 2 details an investigation of endo:exo selectivity in the Diels-Alder reactions of 1,3-butadiene. Chapter 3 explores aspects of the intramolecular Diels-Alder reactions of some substituted 1,3,8-nonatrienes, and Chapter 4 describes the domino Diels-Alder reactions of 1,4-diiodo-1,3-butadiene. The Diels-Alder reaction is powerful, general, and widely used in chemical synthesis, and it is well known that many Diels-Alder reactions exhibit endo selectivity, in accord with Alder’s empirical rule. The origins of endo:exo selectivity in the Diels-Alder reaction, however, are not completely understood and there is a dearth of experimental evidence concerning the Diels-Alder reactions of the archetypal 1,3-diene, 1,3- butadiene. Chapter 2 describes a study of the Diels-Alder reactions of an isotopically labelled 1,3-butadiene with a range of simple dienophiles, allowing the endo:exo selectivities of these important reactions to be determined for the first time. The experimental data shed light on the origins of endo:exo selectivity in the Diels-Alder reaction and will serve as an important reference for future computational investigations in this area. The intramolecular Diels-Alder reaction shares many of the virtues of its intermolecular counterpart, however its use in chemical synthesis is limited because intramolecular Diels-Alder reactivity and stereoselectivity are often governed by subtle factors, and can be very difficult to predict. As part of a comprehensive experimental and computational collaboration, Chapter 3 describes an investigation of the heat and Lewis acid promoted intramolecular Diels-Alder reactions of some ether tethered 1,3,8-nonatrienes. Also presented are the results of a rate study and a kinetic isotope effect study involving the intramolecular Diels-Alder reactions of some 1,3,8-nonatrienes. The experimental data are analysed and compared with predicted stereoselectivities, activation barriers and kinetic isotope effects obtained from computational modelling. Increased efficiency in chemical synthesis conserves resources, reduces waste, and saves time and money. Domino reactions are particularly efficient processes, which can generate complex products from simple reactants. Chapter 4 describes an investigation of the domino Diels-Alder reactions of (1E,3E)-1,4-diiodo-1,3-butadiene with maleimide dienophiles, through which a family of bicyclo[2.2.2]oct-2-ene derivatives are produced in one high yielding and stereoselective synthetic step.
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Частини книг з теми "Endo-exo selectivity"

1

Rastelli, Augusto, Remo Gandolfi, and Mirko Sarzi Amadè. "Regioselectivity and Diastereoselectivity in the 1,3-Dipolar Cycloadditions of Nitrones with Acrylonitrile and Maleonitrile. The Origin of ENDO/EXO Selectivity##Dedicated to professor G.Del Re." In Advances in Quantum Chemistry, 151–67. Elsevier, 2000. http://dx.doi.org/10.1016/s0065-3276(08)60482-7.

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2

Taber, Douglass F. "The Carreira Synthesis of Indoxamycin B." In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0094.

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Some members of the indoxamycin family show potent antineoplastic activity. The key cyclopentene-forming step in the route to indoxamycin B 3 devised (Angew. Chem. Int. Ed. 2012, 51, 3474) by Erick M. Carreira of ETH Zürich was the Pd-catalyzed cyclization of 1 to 2. The starting material for the preparation of 1 was the symmetrical methyl benzoate 4. Dissolving metal reduction followed by alkylation of the resulting ester enolate delivered the diene 5. Reduction and protection followed by allylic oxidation converted 5 into 6, which was carried onto 8 as a mixture of geometric isomers. The dissociated potassium alkoxide of 8 underwent smooth oxy-Cope rearrangement to give an enolate that was trapped as the silyl ether 1. Pd-catalyzed oxidative cyclization then completed the synthesis of 2. With the ketone 2 in hand, two challenges remained: distinguishing the two hydroxymethyl groups and functionalizing the allylic methine to construct the third quaternary center. Both problems were solved by the V-mediated epoxidation of the diol corresponding to 2. In situ, the anti-hydroxyl opened the epoxide to give the cyclic ether. Gold-mediated rearrangement of the O-propargylated enol ether 10 delivered an allene, which was selectively reduced to the alcohol 11. A second gold-mediated cyclization then completed the synthesis of 12. Indoxamycin B had been assigned as having the butenyl sidechain as the more stable endo diastereomer, so the synthesis was initially finished that way. When that product proved to not be congruent with the natural material, it seemed likely that the butenyl sidechain was in fact exo. Selective hydration of 12 gave a mixture of all four alcohol diastereomers. The two exo diastereomers were separated and oxidized to the ketone 13. Wittig olefination gave a pair of geometric isomers that were separated. The cyclic ether of the E isomer 14 was reduced to give a keto alcohol, which was oxidized to the keto aldehyde. Horner-Wadsworth-Emmons chain extension gave 15, which was carried onto indoxamycin B 3. An alternative construction of 3 by intramolecular carbene insertion into the allyic methine of 2 can be imagined.
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3

Taber, Douglass F. "Organocatalytic C–C Ring Construction: Prostaglandin F2α (Aggarwal)." In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0072.

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Marco Lombardo of the Università degli Studi di Bologna devised (Adv. Synth. Catal. 2012, 354, 3428) a silyl-bridged hydroxyproline catalyst that mediated the enantioselective addition of 2 to cinnamaldehyde 1 to give 3. Yoann Coquerel and Jean Rodriguez of Aix Marseille Université showed (Adv. Synth. Catal. 2012, 354, 3523) that a hybrid epi-cinchonine catalyst directed the enantioselective and diastereoselective addition of the amide 4 to the nitro alkene 5 to give 6. Magnus Rueping of RWTH Aachen observed (Angew. Chem. Int. Ed. 2012, 51, 12864) that a chiral Brønsted acid mediated the diastereoselective and enantioselective formation of 9 by the addition of 8 to cyclopentadiene 7. Marco Bandini, also of the University of Bologna, combined (Chem. Sci. 2012, 3, 2859) organocatalysis with gold catalysis to effect the cyclization of 10 to 11. Min Shi of the Shanghai Institute of Organic Chemistry prepared (Chem. Commun. 2012, 48, 2764) the quaternary cyclic amino acid derivative 14 by adding 13 to the acceptor 12. Makoto Tokunaga of Kyushu University prepared (Org. Lett. 2012, 14, 6178) the ketone 17 by the hydrolytic enantioselective protonation of the enol ester 15. Hiyoshizo Kotsuki of Kochi University developed (Synlett 2012, 23, 2554) a dual catalyst combination that effectively mediated the enantioselective addition of malonate even to the congested acceptor 18. Yoshitaka Hamashima and Toshiyuki Kan of the University of Shizuoka established (Org. Lett. 2012, 14, 6016) a protocol for the enantioselective brominative cyclization of 21, readily available by the reductive alkylation of benzoic acid. Polycarbocyclic ring systems can also be prepared by organocatalysis. Ying-Chun Chen of Sichuan University tuned (J. Am. Chem. Soc. 2012, 134, 19942) cinchona-derived catalysts to selectively convert 23 into either exo (illustrated) or endo 25. Peng-Fei Xu of Lanzhou University developed (Angew. Chem. Int. Ed. 2012, 51, 12339) a supramolecular iminium catalyst for the intramolecular Diels-Alder cycloaddition of 26. In a spectacular illustration of the power of organocatalysis, Varinder K. Aggarwal of the University of Bristol dimerized (Nature 2012, 489, 278) succinaldehyde from the hydrolysis of commercial 28 directly to the unsaturated aldehyde 29. Diastereoselective conjugate addition led to prostaglandin F2α 30.
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4

Taber, Douglass. "The Johnson Synthesis of Zaragozic Acid C." In Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0100.

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The zaragozic acids, exemplified by Zaragozic Acid C 3, are picomolar inhibitors of cholesterol biosynthesis. Jeffrey S. Johnson of the University of North Carolina developed (J. Am. Chem. Soc. 2008, 130, 17281) an audacious silyl glyoxylate cascade approach to the oxygenated backbone fragment 1. Intramolecular aldol cyclization converted 1 to 2, setting the stage for the construction of 3. The lactone 2 includes five stereogenic centers, two of which are quaternary. The authors were pleased to observe that exposure of 4 to vinyl magnesium bromide 5 led, via condensation, silyl transfer, condensation, and again silyl transfer, to a species that was trapped with t-butyl glyoxylate 6 to give 7 as a single diastereomer. This one step assembled three of the stereogenic centers of 2, including both of the quaternary centers. The alcohol 7 so prepared was racemic, so the wrong enantiomer was separated by selective oxidation. Intramolecular aldol condensation of the derived α-benzyloxy acetate 1 then completed the construction of 2. Addition of the alkyl lithium 8, again as a single enantiomerically-pure diasteromer, to 2 gave the hemiketal 9. Exposure of 9 to acid initially gave a mixture of products, but this could be induced to converge to the tricyclic ester 10. To convert 10 to 11 , the diastereomer that was needed for the synthesis, two of the stereogenic centers had to be inverted. This was accomplished by exposure to t-BuOK/t-amyl alcohol, followed by re-esterification. The inversion of the secondary hydroxyl group was thought to proceed by retro-aldol/re-aldol condensation. Debenzylation of 11 followed by acetylation delivered 12, an intermediate in the Carreira synthesis of the zaragozic acids. Following that precedent, the ring acetates of 12 were selectively removed, leaving the acetate on the side chain. Boc protection was selective for the endo ring secondary hydroxyl, leaving the exo ring secondary hydroxyl available for condensation with the enantiomerically-pure acid 13. Global deprotection then completed the synthesis of Zaragozic Acid C 3. The key to the success of this synthesis of the complex spiroketal 3 was the assembly of 7 in one step as a single diastereomer from the readily-available building blocks 4, 5, and 6.
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Тези доповідей конференцій з теми "Endo-exo selectivity"

1

Schlachter, I., J. Mattay, J. Suer, U. Höweler, G. Würthwein, and E. U. Würthwein. "Combined quantumchemical and MM-approach to the endo/exo-selectivity of Diels-Alder reactions in polar media." In The first European conference on computational chemistry (E.C.C.C.1). AIP, 1995. http://dx.doi.org/10.1063/1.47869.

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