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Artículos de revistas sobre el tema "Ring-strained alkenes"

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Autor: Grafiati

Publicado: 22 de julio de 2024

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Jeganmohan, Masilamani y Pinki Sihag. "Recent Advances in Transition-Metal-Catalyzed C–H Functionalization Reactions Involving Aza/Oxabicyclic Alkenes". Synthesis 53, n.º 18 (14 de junio de 2021): 3249–62. http://dx.doi.org/10.1055/a-1528-1711.

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AbstractBicyclic alkenes, including oxa- and azabicyclic alkenes, readily undergo activation with facial selectivity in the presence of transition-metal complexes. This is due to the intrinsic angle strain on the carbon–carbon double bonds in such unsymmetrical bicyclic systems. During the past decades considerable progress has been made in the area of ring opening of bicyclic strained rings by employing the concept of C–H activation. This short review comprehensively compiles the various C–H bond activation assisted reactions of oxa- and azabicyclic alkenes, viz., ring-opening reactions, hydroarylation, and annulation reactions.1 Introduction2 Reactions of Heterobicyclic Ring Systems2.1 Ring-Opening Reactions of Oxa- and Azabenzonorbornadienes2.1.1 Reactions Using 7-Oxabenzonorbornadienes2.1.2 Reactions Using 7-Azabenzonorbornadienes2.2 Hydroarylation Reactions2.3 Annulation Reactions2.4 Other Reactions3 Conclusion

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Nishimura, T., T. Hayashi, E. Tsurumaki, T. Kawamoto y X. X. Guo. "Enantioselective Desymmetrization via Ring Opening of Strained Alkenes". Synfacts 2008, n.º 11 (23 de octubre de 2008): 1191. http://dx.doi.org/10.1055/s-0028-1083422.

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Sanzone, Jillian R. y K. A. Woerpel. "High Reactivity of Strained Seven-Membered-Ring trans -Alkenes". Angewandte Chemie International Edition 55, n.º 2 (27 de noviembre de 2015): 790–93. http://dx.doi.org/10.1002/anie.201510056.

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Sanzone, Jillian R. y K. A. Woerpel. "High Reactivity of Strained Seven-Membered-Ring trans -Alkenes". Angewandte Chemie 128, n.º 2 (27 de noviembre de 2015): 800–803. http://dx.doi.org/10.1002/ange.201510056.

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Feng, Qiang, Qian Wang y Jieping Zhu. "Oxidative rearrangement of 1,1-disubstituted alkenes to ketones". Science 379, n.º 6639 (31 de marzo de 2023): 1363–68. http://dx.doi.org/10.1126/science.adg3182.

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The Wacker process, which is widely used to convert monosubstituted alkenes into the corresponding methyl ketones, is thought to proceed through a Pd II /Pd 0 catalytic cycle involving a β-hydride elimination step. This mechanistic scenario is inapplicable to the synthesis of ketones from the 1,1-disubstituted alkenes. Current approaches based on semi -pinacol rearrangement of Pd II intermediates are limited to the ring expansion of highly strained methylene cyclobutane derivatives. Herein, we report a solution to this synthetic challenge by designing a Pd II /Pd IV catalytic cycle incorporating a 1,2-alkyl/Pd IV dyotropic rearrangement as a key step. This reaction, compatible with a broad range of functional groups, is applicable to both linear olefins and methylene cycloalkanes, including macrocycles. Regioselectivity favors the migration of the more substituted carbon, and a strong directing effect of the β-carboxyl group was also observed.

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Shahid, Shereena, Muhammad Faisal, Aamer Saeed, Sarfaraz Ali Ghumro, Hesham R. El-Seedi, Samina Rasheed, Nadir Abbas et al. "A Review on the Scope of TFDO-Mediated Oxidation in Organic Synthesis-- Reactivity and Selectivity". Current Organic Synthesis 15, n.º 8 (17 de diciembre de 2018): 1091–108. http://dx.doi.org/10.2174/1570179415666180831104324.

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Dioxiranes are three-membered strained ring peroxides that are typical archetype examples of electrophilic entities. A dioxirane-based oxidant named 3-methyl(trifluoromethyl)dioxirane (TFDO) is a fluorinated analogue of the extremely valuable oxidant dimethyldioxirane (DMDO). Owing to the strained threemembered ring and presence of electron-withdrawing trifluoromethyl group, TFDO is several times more reactive than DMDO and acts as a significant chemical reagent. Moreover, TFDO exhibits high regio-, chemo- and stereo-selectivity even under unusual reaction conditions, i.e. at pH values close to neutrality and at subambient temperatures. The TFDO transfers an oxygen atom to “unactivated” carbon-hydrogen bonds of alkanes as well as to the double bonds of alkenes and also helps in oxidation of compounds containing heteroatoms having a lone pair of electrons, such as sulfides and amines. TFDO-mediated oxidation is considered to be one of the main procedures in the 21st century for the synthesis of oxygen-containing organic molecules. This review throws light on the applications of TFDO in organic syntheses to provide an insight into the future research and gives a comprehensive summary of the selective functionalization of activated and non-activated organic compounds.

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Ma, Jiajia, Shuming Chen, Peter Bellotti, Tobias Wagener, Constantin Daniliuc, Kendall N. Houk y Frank Glorius. "Facile access to fused 2D/3D rings via intermolecular cascade dearomative [2 + 2] cycloaddition/rearrangement reactions of quinolines with alkenes". Nature Catalysis 5, n.º 5 (mayo de 2022): 405–13. http://dx.doi.org/10.1038/s41929-022-00784-5.

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AbstractHybrid fused two-dimensional/three-dimensional (2D/3D) rings are important pharmacophores in drugs owing to their unique structural and physicochemical properties. Preparation of these strained ring systems often requires elaborate synthetic effort and exhibits low efficiency, thus representing a limiting factor in drug discovery. Here, we report two types of energy-transfer-mediated cascade dearomative [2 + 2] cycloaddition/rearrangement reactions of quinoline derivatives with alkenes, which provide a straightforward avenue to 2D/3D pyridine-fused 6−5−4−3- and 6−4−6-membered ring systems. Notably, this energy-transfer-mediated strategy features excellent diastereoselectivity that bypasses the general reactivity and selectivity issues of photochemical [2 + 2] cycloaddition of various other aromatics. Tuning the aza-arene substitutions enabled selective diversion of the iridium photocatalysed energy transfer manifold towards either cyclopropanation or cyclobutane-rearrangement products. Density functional theory calculations revealed a cascade energy transfer scenario to be operative.

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Sorensen, T. S. y F. Sun. "cis-2,3-Di-tert-butylcyclopropanones". Canadian Journal of Chemistry 75, n.º 7 (1 de julio de 1997): 1030–40. http://dx.doi.org/10.1139/v97-123.

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The preparation of the strained cis-2,3-di-tert-butylcyclopropanone 2 from the acyclic compound, α,α′-dibromodineopentyl ketone 1, using a previously reported methodology, is dramatic evidence of both the existence of oxyallyl intermediates in the mechanism of this reaction, and of the integrity with which oxyallyls ring-close to cyclopropanones by a disrotatory route. Because of the bulky cis substituents, cyclopropanone 2 exhibits a number of unusual spectroscopic features (as compared to the trans isomer 5). With the aid of ab initio calculations on 2 and 5, it can be shown that the C2—C3 bond in 2 interacts with the carbonyl π-orbitals, thus causing the carbonyl oxygen to bend 12° out of the plane; this interaction is absent in 5 and the latter has a planar carbonyl group. As with other cyclopropanones, 2 can be photochemically decarbonylated. This process itself appears to be stereospecific even though highly strained alkenes are produced. Cyclopropanone 2 is thermally rearranged to the trans isomer 5 and the kinetics for this are reported; our favoured mechanism involves oxyallyl intermediates. Other reactions of 2 also appear to proceed through these oxyallyl species; for example, alcohols initially add to 2 to give α-alkoxy ends, solutions of 2 enter into very facile diene cycloadditions, and the dimerization of neat 2 also appears to involve these oxyallyl species. Keywords: cyclopropanones, oxyallyl, stereomutation, stereospecific decarbonylation, nonplanar carbonyl.

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Boutin, Rebecca, Samuel Koh y William Tam. "Recent Advances in Transition Metal-Catalyzed Reactions of Oxabenzonorbornadiene". Current Organic Synthesis 16, n.º 4 (4 de julio de 2019): 460–84. http://dx.doi.org/10.2174/1570179416666181122094643.

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Background: Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate capable of undergoing multiple types of transformations due to three key structural features: a free alkene, a bridged oxygen atom, and a highly strained ring system. Most notably, ring-opening reactions of OBD using transition metal catalysts and nucleophiles produce multiple stereocenters in a single step. The resulting dihydronaphthalene framework is found in many natural products, which have been shown to be biologically active. Objective: This review will provide an overview of transition metal-catalyzed reactions from the past couple of years including cobalt, copper, iridium, nickel, palladium and rhodium- catalyzed reactions. In addition, the recent derivatization of OBD to cyclopropanated oxabenzonorbornadiene and its reactivity will be discussed. Conclusion: It can be seen from the review, that the work done on this topic has employed the use of many different transition metal catalysts, with many different nucleophiles, to perform various transformations on the OBD molecule. Additionally, depending on the catalyst and ligand used, the stereo and regioselectivity of the product can be controlled, with proposed mechanisms to support the understanding of such reactions. The use of palladium has also generated a cyclopropanated OBD, with reactivity similar to that of OBD. An additional reactive site exists at the distal cyclopropane carbon, giving rise to three types of ring-opened products.

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Wanapun, D., K. A. Van Gorp, N. J. Mosey, M. A. Kerr y T. K. Woo. "The mechanism of 1,3-dipolar cycloaddition reactions of cyclopropanes and nitrones A theoretical study". Canadian Journal of Chemistry 83, n.º 10 (1 de octubre de 2005): 1752–67. http://dx.doi.org/10.1139/v05-182.

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The 1,3-dipolar cycloaddition reaction of cyclopropanes and nitrones to give tetrahydro-1,2-oxazine has been studied with density functional theory calculations at the B3LYP/6-31+G(d,p) level of theory. Realistic substituents were modelled including those at the 2-, 3-, 4-, and 6-positions of the final oxazine ring product. The strained σ bond of the cyclopropane was found to play the role of an alkene in a conventional [3+2] dipolar cycloaddition. Two distinct, but similar, reaction mechanisms were found an asymmetric concerted pathway and a stepwise zwitterionic pathway. The reaction barriers of the two pathways were nearly identical, differing by less than ~1 kcal/mol, no matter what the substituents were. The effect of a Lewis acid catalyst was examined and found to have a very large effect on the calculated barriers through coordination to the carbonyl oxygen atoms of the diester substituents on the cyclopropane. The reaction barrier was found to decrease by as much as ~19 kcal/mol when using a BF3 molecule as a model for the Lewis acid catalyst. Solvent effects and the nature of the regiospecificity of the reaction were also examined. Trends in the calculated barriers for the reaction were in good agreement with available trends in the reaction rates measured experimentally. Key words: 1,3-dipolar cycloaddition, cyclopropane, nitrone, tetrahydro-1,2-oxazines, ab initio quantum chemistry, mechanism.

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Shi, Dingcheng, Xingxuan Xia, Binlin Zhao y Yu Yuan. "Diboron-Promoted Iron-Catalyzed Denitrative Vinylation of β-Nitrostyrenes with Cycloketoimes". Organic & Biomolecular Chemistry, 2023. http://dx.doi.org/10.1039/d3ob00890h.

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We have developed a new iron-catalyzed ring opening alkenylation of cycloketoximes with β-nitrostyrenes for the facile synthesis of flexible distal-cyanoalkyl alkenes. Both non-active strained cycloketoximes and less-strained cycloketoximes could be...

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Han, You-Feng, Ying Huang, Hao Liu, Zhong-Hua Gao, Chun-Lin Zhang y Song Ye. "Photoredox cooperative N-heterocyclic carbene/palladium-catalysed alkylacylation of alkenes". Nature Communications 13, n.º 1 (30 de septiembre de 2022). http://dx.doi.org/10.1038/s41467-022-33444-0.

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AbstractThree-component carboacylation of simple alkenes with readily available reagents is challenging. Transition metal-catalysed intermolecular carboacylation works for alkenes with strained ring or directing groups. Herein, we develop a photoredox cooperative N-heterocyclic carbene/Pd-catalysed alkylacylation of simple alkenes with aldehydes and unactivated alkyl halides to provide ketones in good yields. This multicomponent coupling reaction features a wide scope of alkenes, broad functional group compatibility and free of exogenous photosensitizer or external reductant. In addition, a series of chlorinated cyclopropanes with one or two vicinal quaternary carbons is obtained when chloroform or carbon tetrachloride is used as the alkyl halide. The reaction involves the alkyl radicals from halides and the ketyl radicals from aldehydes under photoredox cooperative N-heterocyclic carbene/Pd catalysis.

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Sanzone, Jillian R. y K. A. Woerpel. "ChemInform Abstract: High Reactivity of Strained Seven-Membered-Ring trans-Alkenes." ChemInform 47, n.º 21 (mayo de 2016). http://dx.doi.org/10.1002/chin.201621212.

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Smyth, Megan, Thomas S. Moody, Scott Wharry y Marcus Baumann. "Continuous Flow Synthesis of Cyclobutenes Using LED Technology". Synlett, 4 de mayo de 2023. http://dx.doi.org/10.1055/a-2086-0630.

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Cyclobutenes are highly strained ring systems of considerable synthetic interest that can be accessed via cycloaddition reactions between alkenes and alkynes. However, their traditional preparation relies on photochemical [2+2]-cycloadditions that exploit low wavelength UV radiation emitted from inefficient medium-pressure Hg-lamps. This paper reports on the development of a modern approach using a high-power LED set-up emitting at the boundary of UV-A and visible light in conjunction with a continuous flow reactor. The resulting flow process renders a series of cyclobutenes from maleimides and various commercial alkynes. This provides a more energy-efficient approach that is readily scalable to access multigram quantities of cyclobutenes in high chemical yields and short residence times. The value of these products is exemplified by flow-based hydrogenations yielding highly substituted cyclobutanes which represent sought after building blocks in modern medicinal chemistry programs.

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Du, Yuhui, Yang Yang, Peter Deglmann, Thomas W. Holcombe, Yifeng Du y E. Bryan Coughlin. "The competition between radical copolymerization and charge separation of cyclic ketene acetals and electron‐deficient olefins". Journal of Polymer Science, 15 de septiembre de 2023. http://dx.doi.org/10.1002/pol.20230480.

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AbstractCyclic ketene acetals (CKAs) possess unique features in two aspects. On one hand, after the addition of a radical on the alkene, CKAs can undergo ring‐opening via radical rearrangement, enabling polyester preparation based on chain‐growth polymerization. On the other hand, the alkene connected with two electron‐donating oxygens in a strained form exhibit unique reactivities, resulting in complex reactions in the presence of electron deficient compounds. In this investigation, fundamental studies on CKA radical ring‐opening polymerization and charge‐mediated reactions were performed. Alternating copolymers of CKA and maleimides, or maleates, were prepared and characterized. Quantum chemistry modeling from the perspectives of reaction kinetics and thermodynamics enabled an in‐depth mechanistic study on the side reactions between CKA and maleic anhydride or itaconic anhydride, inspiring the techniques to minimize those side reactions in competition with radical copolymerization. After purifying the anhydride monomers with sublimation, the copolymerization with CKA successfully occurred. The anhydride containing polyester structures with an alternating sequence were confirmed with comprehensive characterizations. Facile post‐functionalization with an alcohol was performed, resulting in carboxylate containing polyesters.

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Moradi, Hanieh, R. Govindarajan, Huy Gia Nguyen, Shubham Deolka, Hoan M. Dinh, Eugene Khaskin, Robert R. Fayzullin, Serhii Vasylevskyi y Julia Khusnutdinova. "Synthesis and Aerobic Oxidation of Perfluoroalkyl d10 Metal Complexes Supported by 2,7‐Dimethyl‐1,8‐naphthyridine". European Journal of Inorganic Chemistry, 23 de mayo de 2024. http://dx.doi.org/10.1002/ejic.202400257.

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The coordination chemistry of 2,7‐dimethyl‐1,8‐naphthyridine has been explored with perfluoroalkyl d10 metals, CuI, ZnII, and AgI. This ligand was shown to form dicoordinate CuI and AgI mono‐perfluoroalkyl complexes where naphthyridine coordinates with only one N‐donor, while bidentate coordination with both N‐atoms was observed in Zn bis(perfluoroalkyl) complexes forming a strained four‐membered chelate ring. Copper complexes undergo facile oxidation in the presence of air or excess O2 to give tetracoordinate CuII complexes coordinated to perfluorocarboxylates formed by oxygenation of the metal‐adjacent α‐CF2 position of the corresponding perfluoroalkyl ligands. Another type of product formed by the oxidation of perfluoroethylcopper(I) complexes in the presence of substoichiometric O2 are binuclear CuI‧‧‧CuI complexes with two perfluorocarboxylate ligands. In the presence of an external substrate, alkene, O‐atom transfer was observed to give oxygenated products, resembling the recently reported O‐transfer reactivity of naphthyridine‐supported Ni long‐chain perfluoroalkyl complexes.

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