Relevant bibliographies by topics / Umpolung

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters

Academic literature on the topic 'Umpolung'

Author: Grafiati
Published: 4 June 2021
Last updated: 7 July 2024

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Journal articles on the topic "Umpolung"

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J. Boluda, Carlos, Carolina Juncá, Emily Soto, Darah De la Cruz, and Anny Peña. "Umpolung in reactions catalyzed by thiamine pyrophosphate dependent enzymes." Ciencia, Ambiente y Clima 2, no. 2 (December 13, 2019): 27–42. http://dx.doi.org/10.22206/cac.2019.v2i2.pp27-42.

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El intercambio temporal del carácter electrofílico/nucleofí-lico de un átomo mediante manipulación química, es cono-cido con el vocablo alemán de umpolung. Esta inversión de polaridad permite explorar nuevas posibilidades sintéticas que no pueden llevarse a cabo partiendo de la reactividad normal de los grupos funcionales. Se trata de una herra-mienta sintética útil, que también es utilizada por ciertas enzimas en determinadas reacciones bioquímicas que tienen lugar en las células. Las enzimas dependientes del pirofosfato de tiamina, como la piruvato descarboxilasa, la piruvato deshidrogenasa, la α-cetoglutarato deshidrogenasa, la deshidrogenasa de α-cetoácidos de cadena ramificada y la transcetolasa, proporcionan ejemplos claros de umpolungen reacciones celulares. En esta revisión, tras una discusión sobre el significado del término umpolung encontrado en la literatura química, se analizan los mecanismos de reacción y el significado bioquímico de las transformaciones llevadas a cabo por las enzimas mencionadas.
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Sukhorukov, Alexey Yu. "Umpolung of Enamines: An Overview on Strategies and Synthons." Synlett 31, no. 05 (January 13, 2020): 439–49. http://dx.doi.org/10.1055/s-0037-1610741.

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Umpolung strategies are of considerable interest to organic chemists because they provide alternative synthetic routes to those imposed by the natural polarity of classical synthons. Reverse-polarity reactions of aldehydes, α,β-unsaturated carbonyl compounds, and imines are deeply embedded in the methodology of organic synthesis. In recent years, umpolung of enols and enamines has received much attention as a novel strategy to access α-substituted ketones. Here, state-of-the-art approaches to umpolung of enamine reactivity are discussed, with a particular focus on recent developments in this field from the author’s research group.1 Introduction2 Approaches toward Umpolung of Enamines3 Umpolung of Enamines through Single-Electron Oxidation4 Azadienes as Synthetic Equivalents of Enamine Umpolung Synthons5 Enamines Possessing a Leaving Group at the Nitrogen Atom6 Enamines Possessing a Directing Group at the Nitrogen Atom7 Summary and Outlook
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Huang, Zhusheng, Qingqing Chen, Xiuqin Yang, Yang Liu, Li Zhang, Tao Lu, and Qingfa Zhou. "Phosphine-mediated domino reactions of phthalimidomalonates with allenoates or but-2-ynoate: facile entry into highly functionalized pyrroloisoindolinone derivatives." Organic Chemistry Frontiers 4, no. 6 (2017): 967–71. http://dx.doi.org/10.1039/c6qo00775a.

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A phosphine-mediated γ-umpolung/Wittig/γ-umpolung reaction between phthalimidomalonates and allenoates/but-2-ynoate furnishes highly functionalized pyrroloisoindolinone derivatives in synthetically useful yields.
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Sun, Xi-Shang, Xin Chang, Li-Min Shi, Zuo-Fei Wang, Liang Wei, and Chun-Jiang Wang. "Palladium catalyzed cascade umpolung allylation/acetalation for the construction of quaternary 3-amino oxindoles." Chemical Communications 57, no. 64 (2021): 7958–61. http://dx.doi.org/10.1039/d1cc03075b.

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A highly diastereoselective synthesis of quaternary 3-amino oxindoles via a palladium catalyzed three-component cascade umpolung allylation/acetalation process has been developed. The current method could be extended to cascade umpolung allenylation/acetalation.
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Hou, Yading, Yuwen Zhang, and Xiaofeng Tong. "Phosphine-catalysed α-umpolung addition of nucleophiles to δ-acetoxy allenoates: stereoselective synthesis of 2,4-dienoates." Organic & Biomolecular Chemistry 16, no. 29 (2018): 5245–49. http://dx.doi.org/10.1039/c8ob00933c.

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The first example of phosphine-catalyzed α-umpolung addition of nucleophiles to allenoates is described, which features the use of δ-acetoxy allenoate to generate a 3-phosphonium-2,4-dienoate intermediate, thus facilitating the α-umpolung addition of nucleophiles.
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Finkbeiner, Peter, and Boris J. Nachtsheim. "Umpolung von Iminen." Nachrichten aus der Chemie 63, no. 11 (November 2015): 1089–93. http://dx.doi.org/10.1002/nadc.201590367.

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Allmann, Rudolf, Wolfgang Hanefeld, Magda Krestel, and Bernd Spangenberg. "A Sulfene Umpolung." Angewandte Chemie International Edition in English 26, no. 11 (November 1987): 1133–34. http://dx.doi.org/10.1002/anie.198711331.

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Zhao, Baoguo, and Wen-Wen Chen. "Decarboxylative Umpolung Synthesis of Amines from Carbonyl Compounds." Synlett 31, no. 16 (July 12, 2020): 1543–50. http://dx.doi.org/10.1055/s-0040-1707157.

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2-Azaallyl anions are valuable intermediates which have versatile applications in functionalization with various electrophiles. Decarboxylation of the imines formed from aromatic aldehydes and α,α-diphenylglycine provides an interesting and efficient way to generate delocalized 2-azaallyl anions, which display high reactivity toward different electrophiles with excellent regioselectivity at the diphenylketimino aryl carbon of the 2-azaallyl anions. The transformation produces various amines in good yields under very mild conditions. This Synpacts article highlights the recent advances on the decarboxylative umpolung synthesis of amines from carbonyl compounds.1 Introduction2 Decarboxylative Umpolung Reactions of Carbonyl Compounds with Different Electrophiles2.1 Reaction with π-Allyl–Pd(II) Species2.2 Reaction with Morita–Baylis–Hillman Adducts2.3 Reaction with Imines2.3.1 Intermolecular Reaction with N-Ts Imines2.3.2 Intramolecular Reaction with Chiral N-tert-Butanesulfinyl Imines2.4 Reaction with Aldehydes and Ketones3 Decarboxylative Umpolung Reaction of α,β-Unsaturated Aldehydes with Aldehydes4 Conclusion
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Jaenicke, Lothar. "Umpolung der Peptid-Synthese." Chemie in unserer Zeit 44, no. 5 (October 2010): 319. http://dx.doi.org/10.1002/ciuz.201090065.

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Korte, Monia. "Die Umpolung des Erdmagnetfelds." Physik in unserer Zeit 50, no. 6 (November 2019): 308. http://dx.doi.org/10.1002/piuz.201970613.

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Dissertations / Theses on the topic "Umpolung"

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Ryzhakov, Dmytro. "Désaromatisation radicalaire d'indoles pour la synthèse de spiroindolines trifluorométhylées ou phosphorées." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS366.

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Les spirooxindoles se retrouvent fréquemment dans les produits naturels et les composés biologiquement actifs. Certains principes actifs pharmaceutiques contenant un motif spirooxindole ont également été décrits, stimulant un grand intérêt pour la construction et la modification de ce squelette. Cependant, peu de travaux ont été réalisés pour remplacer le carbonyle en position 2 par un autre groupe fonctionnel d’intérêt. Basées sur l’expertise reconnue de notre équipe en désaromatisation d’indoles par umpolung et l’importance des fonctions CF₃ et PO(OR)₂ nous avons entrepris la synthèse de 3,3-spiroindolines substitueés en position 2 par un trifluoromethyl ou un phosphonate. Nous avons ainsi généré des radicaux trifluoromethyl ou phosphonyl par oxydation respective de trifluoromethyl sulfinate de sodium et de phosphites. Les espèces radicalaires obtenues peuvent ensuite s’additionner sur la position 2 des indoles et effectuer la désaromatisation d’indoles
Spirooxindoles are frequently found in natural products and biologically active compounds. Certain pharmaceutical active ingredients containing a spirooxindole motif have also been described, stimulating great interest in the construction and modification of this structures. However, not a lot of work has been done to replace the carbonyl in position 2 with another functional group of interest. Based on the recognized expertise of our team in deflation of indoles by umpolung and the importance of CF₃ and PO(OR)₂ functions, we have undertaken the synthesis of 3,3-spiroindolines substituted in position 2 by a trifluoromethyl or a phosphonate . We have thus generated trifluoromethyl or phosphonyl radicals by respective oxidation of sodium trifluoromethyl sulfinate and phosphites. The radical species obtained can then be added to the position 2 of the indoles and perform the dearomatization of indoles
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Knappke, Christiane [Verfasser]. "Untersuchungen zur Umpolung von Alkylhalogeniden durch N-heterocyclische Carbene / Christiane Knappke." München : Verlag Dr. Hut, 2011. http://d-nb.info/1011441578/34.

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Patra, A. "N-heterocyclic carbene-organocatalyzed umpolung of aldehydes and imines for new synthetic transformations." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2017. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4272.

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Esgulian, Mathieu. "Oxyhomologation diastéréosélective de la sérine : développement de la méthodologie MAC." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS392/document.

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La méthodologie MAC consiste à employer des réactifs umpolung pour permettre l’insertion formelle d’une fonction carbonyle entre un électrophile et un nucléophile. Cette thèse est consacrée à l’oxyhomologation diastéréosélective de la L-sérine grâce à un développement significatif de la méthodologie MAC à trois composants en one-pot, conduisant à l’obtention de dérivés orthogonalement protégés de l’acide α, γ-dihydroxy-β-aminobutyrique. Ce dernier est une brique moléculaire acyclique à 4 atomes de carbone hautement fonctionnalisée qui est souvent intégrée dans les squelettes de molécules biologiquement actives.Nous avons tout d’abord étudié la synthèse de réactifs MAC silylés à partir du malononitrile. La synthèse du H-MAC-TBS a été optimisée et deux nouveaux réactifs MAC silylés, le H-MAC-TES et le H-MAC-TBDPS, ont été préparés.Dans un premier temps, nous avons étudié l’oxyhomologation du N-Boc-O-Bn-L-sérinal avec le H-MAC-TBS en présence de différents alcools dans des conditions réactionnelles douces. En présence de méthanol, des α, γ-dihydroxy-β-aminobutanoates de méthyle orthogonalement protégés ont été préparés avec des bons rendements et avec un ratio diastéréoisomérique syn/anti = 80/20.L’utilisation du H-MAC-TBDPS a permis d’améliorer la diastéréosélectivité de la réaction MAC (syn/anti = 90/10). L’étude des différents modes de cyclisation des α, γ-dihydroxy-β-aminobutanoates de méthyle a été réalisée par la suite. Des hétérocycles fonctionnalisés à 3, 5 et 6 chaînons ont été ainsi sélectivement synthétisés.De nouvelles oxazolidinones et oxazolines hautement fonctionnalisées ont été préparées de cette façon. En revanche, malgré nos efforts approfondis, une cyclisation pour donner un hétérocycle à 4 chaînons n’a pas été réalisée.L’absence de réactivité de la fonction alcool libre en α de ces esters N-protégés et γ activés a été inattendue.Dans un deuxième temps, nous avons étudié l’oxyhomologation de l’aldéhyde de Garner, un dérivé cyclique N,O-protégé du L-sérinal, par des réactions MAC. En présence de divers nucléophiles, cette réaction a conduit diastéréosélectivement à des esters et des amides protégés de l’acide α, γ-dihydroxy-β-aminobutyrique avec des bons rendements et avec une diastéréoselectivité anti, allant jusqu’à un ratio diastéréoisomérique syn/anti = 10/90 en utilisant le H-MAC-TBDPS. Il s’agit des premiers exemples de diastéréosélectivité antiobservée pour une réaction MAC. Des hétérocycles fonctionnalisés à 3 et 5 chaînons ont été sélectivement synthétisés et, grâce à une oxydation sélective en position γ, des dérivés de l’acide érythro-β-hydroxyaspartique et de l’érythro-β-hydroxyasparagine orthogonalement protégés ont été préparés
MAC methodology is a synthetic technique which employs an umpolung reagent to formally insert a carbonyl function between an electrophile and a nucleophile. This thesis is devoted to the diastereoselective oxyhomologation of L-serine thanks to a significant development of 3-component one pot MAC methodology, providing a synthesis of orthogonally-protected derivatives of α, γ-dihydroxy-β-aminobutyric acid. This latter is a highly functionalized, acyclic, 4-carbon molecular building block which is a constituent part of various biologically active molecules.The synthesis of silylated MAC reagents from malononitrile was first studied. H-MAC-TBS’s synthesis was optimized and two new silylated MAC reagents, H-MAC-TES and H-MACTBDPS,were prepared.In a first study, the oxyhomologation of N-Boc-O-Bn-L-serinal was examined using H-MACTBS and a panel of alcohols in mild conditions.Methyl esters of orthogonally-protected α, γ-dihydroxy-β-aminobutanoic acid were prepared in good yields and with a diastereoisomeric ratio syn/anti = 80/20. The use of H-MAC-TBDPS improved the diastereoselectivity of the MAC reaction to syn/anti = 90/10.Subsequently, different cyclization modes of methyl α, γ-dihydroxy-β-aminobutanoate were investigated, leading to the selective synthesis of functionalized 3-, 5- and 6-membered ring heterocycles, including new highly functionalized oxazolidinones et oxazolines. In contrast, despite considerable efforts, we were unable to induce cyclisation to forma a 4-membered ring heterocycle, due to the surprising lack of nucleophilicity of the free alcohol function in the acyclic precursors.In a second study, we examined the oxyhomologation of Garners aldehyde, a cyclicN,O-protected derivative of L-serinal, using a selection of nucleophiles via one-pot MAC methodology. These reactions furnished protected ester and amide derivatives of α, γ-dihydroxy-β-aminobutyric acid in good yields with an anti diastereoselectivity with a ratio as high as syn/anti = 10/90 when H-MAC-TBDPS was used as the MAC reagent. These are the first known examples of MAC reactions which proceed with anti diastereoselectivity.Functionalized 3- and 5-membered ring heterocycles were prepared from these adducts,and via selective oxidation at the γ-position,orthogonally-protected derivatives of erythro-β-hydroxyaspartic acid and erythro-β-hydroxyasparagine were prepared
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RAGNO, Daniele. "Reactivity of Alpha-Diketones in Umpolung Catalysis and Enantioselective Sulfoxidation by Novel Titanium Complexes." Doctoral thesis, Università degli studi di Ferrara, 2016. http://hdl.handle.net/11392/2403389.

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Nella continua ricerca di metodologie atte alla formazione di nuovi legami carbonio-carbonio, l’organocatalisi svolge un ruolo sempre più fondamentale; in questo contesto, la catalisi di Umpolung, che prevede l’inversione di reattività di un dato substrato, rappresenta un’importante via per accedere a nuove strategie sintetiche. All’interno di quel gruppo di molecole in grado di fornire reattività di umpolung, gli α-dichetoni rappresentano senza dubbio substrati molto interessati ed innovativi. Alla luce di queste premesse, la reattività di α-dichetoni di-arilici è stata oggetto dei nostri studi. Inizialmente è stata valutata la reattività in reazioni di tipo cross-benzoinico con aldeidi, introducendo un nuovo catalizzatore di umpolung, il metil solfonil (dimsile) carbanione, con ottimi risultati in termini di efficienza di reazione e di chemoselettività. La messa a punto di questa metodologia ha inspirato lo sviluppo di un nuova strategia sintetica per l’accesso a 1,2-dichetoni asimmetrici, che ha previsto una prima reazione cross-benzoinica catalizzata dall’anione dimsile , seguita da un’ossidazione in situ con riscaldamento a microonde. Successivamente, si è passati all’impiego di α-dichetoni di-arilici in reazioni di addizione nucleofila con accettori di Michael; in questo caso è stata sviluppata una nuova reazione di doppia aroilazione catalizzata dal metil solfonil anione. E’ stato infine conferito un ulteriore valore aggiunto ai prodotti di reazione grazie ad un successivo stadio ossidativo, che ha consentito l’accesso ai corrispettivi alcheni tetrasostituiti. Inoltre, uno degli aspetti più rilevanti della nostra attività di ricerca è consistito nell’indagine meccanicistica supportata da misure di tipo NMR ed ESI-MS. In questo contesto, è stato recentemente condotto lo studio ESI-MS della reazione di ossidazione aerobica di aldeidi catalizzata, da N-eterociclo carbeni (NHC). Mediante l’utilizzo di un NHC opportunamente funzionalizzato è stato possibile individuare le diverse specie e gli equilibri coinvolti nel processo catalitico. Alla luce dell’esperienza pregressa del mio gruppo di ricerca nel campo della chimica in flusso, diversi processi di umpolung, quali reazioni di tipo benzoinico, aciloinico e di Stetter, sono stati studiati utilizzando microreattori monolitici tiazolio-funzionalizzati in regime di flusso. Infine, durante il periodo svolto presso il gruppo del Prof. Berkessel, l’attività di ricerca si è incentrata sulla sintesi e l’impiego di ligandi cis-DACH-salalen in reazioni di solfossidazione stereoselettiva catalizzate da complessi di Titanio, utilizzando H2O2 come ossidante; durante questo lavoro è stato messo a punto un solido protocollo per lo step di solfossidazione enantioselettiva della sintesi dell’esomeprazolo.
In the investigation of effective chemical transformations, organocatalyzed carbon-carbon bond forming reactions play an outstanding role. Particularly, the inversion of the typical reactivity of a given substrate (umpolung) opens up new and unconventional synthetic pathways. In the continuous research of new acyl anion precursors, α-diketones actually represent innovative and efficient substrates. In this regard, the it was studied the umpolung reactivity of α-diketones confirming their crucial role as acyl anion precursors; after previous investigations by our group on dialkyl diketones, we focused our research on diaryl diketones. First, their reactivity in the cross-benzoin reaction with aldehydes was evaluated, introducing a new umpolung catalyst, the methyl sulfinyl (dimsyl) anion, with great results in terms of yields and chemoselectivity. This new optimized procedure opened a new synthetic route towards the synthesis of unsymmetrical αdiketones, thanks to a one-pot two-step process that involved a first cross-benzoin reaction catalyzed by the dimsyl anion, followed by in situ oxidation performed under microwave conditions. As a logical development of our research, the reactivity of diaryl 1,2-diketones with Michael acceptors in “Stetter-like” reactions was investigated; a new double aroylation reaction catalyzed by the methyl sulfinyl carbanion was discovered. The utility of the resulting 2-benzoyl-1,4-diones was also demonstrated by their facile conversion into the corresponding tetrasubstituted olefins. Investigation of reaction mechanisms by NMR and ESI-MS analysis represented an important part of our work. In this regard, a charge-tagged N-heterocyclic carbene (NHC) was employed as mass spectrometric probe to identify the species involved in the different oxidation steps of the aerobic NHC-catalyzed oxidation of aldehydes. Moreover, in continuation of the reserach of our group in the flow chemistry field, we prepared thiazolium-functionalized monolithic microreactors and demonstrated their synthetic potential in continuous-flow umpolung transformations such as benzoin, acyloin-type, and Stetter reactions. Finally, during my period in Prof. Berkessel group, a series of cis-DACH-derived salalen ligands were synthetized and their activity evaluated in the titanium-catalyzed asymmetric sulfoxidation of thioethers with aqueous hydrogen peroxide; a solid methodology for the last enantioselective sulfoxidation step of Esomeprazole synthesis was developed.
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Le, Xuan-Tien. "Nouvelles réactions d’allylations induites par le samarium divalent. Application à la modification contrôlée de dérivés de l’acide sialique." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112073.

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Le couplage croisé entre les esters allyliques et les composés carbonylés promu par le diiodure de samarium est une méthode efficace pour la formation de liaisons carbone-carbone. Une approche « umpolung » de réaction entre un composé carbonylé électrophile et un allylsamarien nucléophile, obtenu sans la réduction préalable d’espèces de type π-allylmétal de transition intermédiaires, fournirait une nouvelle voie plus simple pour la construction de cette liaison dans des conditions douces.Les esters allyliques de type dihydropyranyle se sont montrés d’excellents substrats dans les réactions d'allylation, d’aldéhydes ou de cétones, induites par le diiodure de samarium évitant ainsi l'utilisation de catalyseurs au palladium ou d’un autre additif. En série glycal, la nature et la configuration du substituant en position C-4 jouent un rôle très important à la fois sur le rendement et sur la structure des produits modifiés. Les couplages réducteurs directs ont lieu régiosélectivement en C-3 avec une stéréochimie relative 3,4-trans. La même stratégie appliquée aux dérivés Neu5Ac2en de l’acide sialique a permis d’obtenir par réactions à basse température, les produits de couplage en C-2 avec des rendements quantitatifs et une parfaite régio- et stéréosélectivité. Cette transformation donne un nouvel accès facile, rapide et très efficace aux α-C-sialosides
The cross-coupling of allylic esters and carbonyl compounds promoted by samarium diiodide is an efficient method for the formation of carbon-carbon bonds. An umpolung approach, reaction between a carbonyl electrophile and an allyl samarium nucleophile, without the prior reduction of the intermediate π-allyl transition metal complexes, would provide a simple route for this bond construction under mild conditions.Dihydropyranyl allylic esters have been found to be excellent substrates for carbonyl allylation reactions mediated by samarium diiodide – without the use of palladium catalysts or any other additive. In glycal series, the nature and the configuration of the substituent at the C-4 position play crucial roles both on yields and structures of the modified products. The direct reductive couplings take place regioselectively at C-3 with a 3,4-trans relationship. Applied to Neu5Ac2en derivatives of sialic acid, the same strategy furnished the coupling products at the anomeric position in quantitative yields and with a perfect regio- and stereoselectivity. This transformation provides an easy, rapid and efficent access to α-C-sialosides
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Vogt, Monika [Verfasser]. "Umpolung von Allyl-Palladium-Komplexen und Anwendung in der Synthese von Naturstoff-Fragmenten / Monika Vogt." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover, 2010. http://d-nb.info/1008410608/34.

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Kipke, Andreas [Verfasser]. "Kupfer-katalysierte oxidative Decarbonylierung chiraler Aldehyde und Untersuchungen zur Umpolung von Allyl-Palladium-Komplexen / Andreas Kipke." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1029588872/34.

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DI, CARMINE Graziano. "Organo- and bio-catalytic approaches to the synthesis of biologically relevant compounds by the Umpolung strategy." Doctoral thesis, Università degli studi di Ferrara, 2019. http://hdl.handle.net/11392/2488244.

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The design of new reactions for carbon-carbon bond formation is certainly the main field in which the efforts of organic chemists have been focused in the last forty years. In addition, the undoubted benefit brought by catalysis has made possible the exploration of new and previously unknown reactivities, which have paved the way for the synthesis of complex molecules in a more efficient manner. In this regard, our group has been involved for years in the investigation of the reversal reactivity of substrate molecules (umpolung), and during my period as Ph.D. student the activity has been mostly devoted to the exploration of this type of reactivity through two main catalytic approaches, namely organocatalysis and biocatalysis. The organocatalytic strategy was successfully employed in the synthesis of imidazoline-2-thiones via a domino process, which was characterized by the formation of a new carbon-carbon bond through an aza-benzoin reaction promoted by a N-Heterocyclic Carbene (NHC) catalyst. Afterwards, a new protocol was developed for the chemo- and enantioselective dearomatization of activated pyridinium salts through the NHC-catalyzed nucleophilic addition of umpoled aldehydes. Finally, the last work based on an organocatalytic approach dealt with the desymmetrization of 1,4-dihydropyridines by chiral NHC-oxidative catalysis. In the context of biocatalysis, the synthetic potential of the enzyme/substrate pair Acetoin: Dichlorophenolindophenol Oxidoreductase from Bacillus licheniformis / methyl acetoin was efficiently exploited for the preparation of optically active phenyl acetyl carbinols ((S) -PACs). In addition, the same enzyme / substrate pair was demonstrated to be extremely effective in the synthesis of dissymmetric acyloins. At the end of my doctoral course, during my period abroad in the group of Prof. Darren J. Dixon at the University of Oxford, I was involved in a research program dealing with the activation of amides promoted by Iridium complexes. In this regard, a new methodology was developed for the synthesis of substituted pyrrolidines, which were obtained through 1,3-dipolar cyclization reactions between acrylates and azomethine ylides generated in situ by catalysis with the Vaska complex in a reductive environment.
La progettazione di nuove reazioni che permettono la formazione di legami carbonio-carbonio è sicuramente il campo principale in cui si sono focalizzati gli sforzi dei chimici organici negli ultimi quarant’anni. In aggiunta, l’indubbio beneficio portato dalla catalisi in tale ambito ha reso possibile l’esplorazione di nuove reattività prima sconosciute, che hanno spianato la strada alla sintesi di molecole complesse, in maniera sempre più efficiente. Su questa linea, il nostro gruppo si è inserito da anni con la premessa di esplorare in maniera critica la reattività che porta all’inversione della naturale polarità nei substrati, e durante il mio periodo di dottorato l’attività svolta ha previsto l’indagine di tale reattività attraverso i suoi due approcci più importanti (organocatalisi e biocatalisi). La via organocatalitica è stata impiegata con successo nella sintesi di imidazoline-2-tioni mediante un processo domino che ha coinvolto la formazione di un nuovo legame carbonio-carbonio, tramite una reazione aza-benzoinica promossa da un carbene N-eterociclico (NHC acronimo del termine inglese N-Heterocyclic Carbene). A seguire è stato messo a punto un protocollo per la dearomatizzazione di sali di piridinio, attivati da un gruppo elettron-attrattore in posizione 3 dell’anello. Questi ultimi hanno ricoperto il ruolo di elettrofili nell’addizione di aldeidi attivate da NHC chirali. Ed infine, l’ultimo lavoro inerente l’organocatalisi, ha riguardato la desimmetrizzazione di 1,4-diidropiridine tramite catalisi da NHC chirali in ambiente ossidativo. Nell’ambito della biocatalisi la coppia enzima/substrato, Acetoin:Dichlorophenolindophenol Oxidoreductase from Bacillus licheniformis / metil acetoino, è stata impiegata efficacemente nella preparazione di fenil acetil carbinoli otticamente attivi ((S)-PAC). In aggiunta, la medesima coppia enzima/substrato si è rivelata essere estremamente efficiente per sintesi enantioselettiva di aciloini dissimmetrici. Al termine del mio percorso dottorale, durante il mio periodo svolto all’estero presso il gruppo del Prof. Darren J. Dixon (Università di Oxford), mi sono occupato dell’attivazione di ammidi mediante complessi di Iridio. Nella fattispecie è stata sviluppata una metodologia che porta alla sintesi di pirrolidine sostituite, attraverso una reazione di ciclizzazione 1,3-dipolare, resa possibile dalla formazione in situ di azometinilidi grazie alla reattività del complesso di Vaska in ambiente riduttivo.
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10

Marquet, Bernard. "Electrofluoration en position benzylique." Lyon 1, 1990. http://www.theses.fr/1990LYO10196.

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L'oxydation anodique de derives benzyliques fonctionnalises dans cette position par un groupement electro-attracteur (carbonyle, nitrile, sulfonate) dans l'acetonitrile en presence de trihydrofluorure de triethylamine permet d'introduire un atome de fluor sur le chainon benzylique, via un mecanisme transitant par un carbocation destabilise. En serie paramethoxylee, les mono et les difluorures benzyliques sont obtenus avec de bons rendements quel que soit le groupement electro-attracteur. Pour les autres structures, la formation concurrentielle d'acetamide, ainsi qu'une fluoration du noyau aromatique sont observees. L'utilisation du sulfolane comme solvant en remplacement de l'acetonitrile permet d'eviter l'acetamidation. La fluoration de derives paramethyles a ete egalement etudiee. Elle conduit a une fonctionnalisation regioselective de ces composes. Les principaux facteurs responsables de cette regioselectivite ont ete examines
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Books on the topic "Umpolung"

1

Wallimann, Silvia. Die Umpolung: Vom Materiellen zum Geistigen. 2nd ed. Freiburg im Breisgau: Verlag Hermann Bauer, 1989.

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Wallimann, Silvia. Die Umpolung. Vom Materiellen zum Geistigen. Bauer, Freiburg, 2000.

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Book chapters on the topic "Umpolung"

1

Podbregar, Nadja. "Magnet Erde - kommt die große Umpolung?" In Im Fokus: Geowissen, 33–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-34791-7_3.

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Schmittel, Michael. "Umpolung of ketones via enol radical cations." In Electron Transfer I, 183–230. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/3-540-57565-0_76.

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3

"Phosphorus Containing Umpolung Reagents." In Handbook of Organophosphorus Chemistry, 253–88. CRC Press, 1992. http://dx.doi.org/10.1201/9781482277241-8.

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"Phosphorus Containing Umpolung Reagents." In Handbook of Organophosphorus Chemistry, 253–88. CRC Press, 1992. http://dx.doi.org/10.1201/9781482277241-8.

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5

Sakander, Norein, Ajaz Ahmed, Bisma Rasool, and Debaraj Mukherjee. "An Overview of N-heterocyclic carbene: Properties and Applications." In Electrophile and Lewis Acid [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.1001331.

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N-Heterocyclic carbenes are regarded as neutral compounds containing a divalent carbon atom with a six-electron valence shell, carbenes are an intriguing class of carbon-containing compounds. The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. They are cyclic molecules that contain one carbene and at least one nitrogen atom within the carbene-containing ring structure. These molecules are widely used as ancillary ligands for the preparation of transition-metal-based catalysts and also possess a unique characteristic feature i.e. Umpolung nature. The underlying principle of many of the NHC-catalyzed reactions is the remarkable ability of NHCs to reverse the normal mode of reactivity of aldehydes (umpolung). NHCs can catalyze transformations proceeding via the umpolung or nonumpolung mode for the synthesis of various functionalized molecules.
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6

Fan, Y. C., and O. Kwon. "Phosphine-Catalyzed γ-Umpolung Addition." In Lewis Base and Acid Catalysts, 1. Georg Thieme Verlag KG, 2012. http://dx.doi.org/10.1055/sos-sd-204-00368.

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Fan, Y. C., and O. Kwon. "Phosphine-Catalyzed α-Umpolung Addition." In Lewis Base and Acid Catalysts, 1. Georg Thieme Verlag KG, 2012. http://dx.doi.org/10.1055/sos-sd-204-00386.

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Narayana, Yatheesh, Sandhya N.C., H. E. Dinesh, Sridhar B. Thimmaiah, Kanchugarakoppal S. Rangappa, and Kempegowda Mantelingu. "N-Heterocyclic Carbene Mediated Organocatalysis Reactions." In Carbene. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.100642.

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Arduengo et al., isolated the first ‘bottleable’ carbene, the first N-heterocyclic carbene (NHC) 1,3-di(adamantyl)imidazol-2-ylidene resulted to an explosion of experimental and theoretical studies of novel NHCs being synthesized and analyzed have huge practical significance. These compounds emerged as successful ligands for coordinating transition metals, the complexes with NHC show diverse applications in the field of catalysis and organic transformation, NHC as ligand to main group elements and their properties and applications. Here this chapter provides the concise overview of N-heterocycle carbene as an organocatalyst that provides different organic transformation on to a carbonyl group. The majority of the NHC catalyzed reactions are employed in the phenomenon of reversing the electrophilic character of carbonyl carbon to nucleophilic carbon (umpolung activity) on coordination suggests benzoin, Stetter and hydroacylation reactions. Also, non-umpolung activity of bis-electrophile α,β-unsaturated acylazoliums reaction with suitable bis-nucleophiles in the organic synthesis have been studied.
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Fan, Y. C., and O. Kwon. "Phosphine-Catalyzed Umpolung-Michael Reaction of Allenoates." In Lewis Base and Acid Catalysts, 1. Georg Thieme Verlag KG, 2012. http://dx.doi.org/10.1055/sos-sd-204-00382.

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Fan, Y. C., and O. Kwon. "γ-Umpolung Addition Using a Chiral Phosphepin." In Lewis Base and Acid Catalysts, 1. Georg Thieme Verlag KG, 2012. http://dx.doi.org/10.1055/sos-sd-204-00406.

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