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The asymmetric total synthesis of (+)-geniposide via phosphine-catalyzed [3+2] cycloadditionJones, Regan Andrew 03 September 2009 (has links)
The iridoids are a large family of monoterpenoid natural products that possess a wide range of biological activities. A great deal of research has already been done in the field of iridoid total synthesis, but limitations still remain. Specifically, few syntheses of iridoid β-glycosides have been reported. This work describes the 14 step asymmetric total synthesis of the iridoid β-glycoside (+)-geniposide utilizing a phosphine-catalyzed [3+2] cycloaddition as the key step. Other noteworthy steps in the synthesis include a palladium-catalyzed kinetic resolution and a previously unutilized method for iridoid glycosidation. In addition to describing the synthesis of (+)-geniposide, this dissertation will also review 1) phosphine-catalyzed cycloaddition reactions and 2) previous enantioselective total syntheses of iridoid glycosides. / text
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Synthetic Studies of Polysubstituted Pyroglutamates and Its Applications in Natural Products SynthesisSun, Pei-Pei 03 July 2003 (has links)
We have explored a formal [3+2] strategy that is synthetically useful for constructing polysubstituted pyroglutamates with three contiguous chiral centers in one step. Base-induced coupling/cyclization reactions of a-sulfonylacetamide with various ethyl (Z)-2-bromo-2-propenoates have been carried out. This reaction with high diastereoselectivity has been applied to the synthesis of Rolipram, Chlorpheg, Baclofen, Pseudoheliotridane and Kainic acid.
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Intermolecular [3+2] Cycloadditions of Imino-isocyanates to Access β-Amino Carbonyl CompoundsBongers, Amanda L. January 2017 (has links)
In modern synthetic organic chemistry, chemists are driven to develop efficient methods for important C-C and C-N bond formation reactions. The challenge lies with establishing new uses for readily available substrates. In this regard, the synthesis of β-aminocarbonyl compounds from alkenes remains a long-standing challenge. Innovation in reaction discovery often requires finding new reagents, or rare reagents with underappreciated value in synthesis. In Chapter 1, N-isocyanates and other heterocumulenes are introduced as versatile amphoteric reagents. Their amphoteric properties are valuable in the discovery of new synthetic approaches, especially in cycloaddition reactions. While C-isocyanates are bulk industrial chemicals, the formation and reactivity of N-isocyanates remains underexplored.
Chapter 2 describes the development of reactivity with rare imino-isocyanates. This includes methods to access the reagent in situ with a blocking group approach, and the establishment of intermolecular cycloaddition reactivity with a variety of alkenes. This stereospecific reaction provides complex N,N’-cyclic azomethine imines, and enables access to β-aminocarbonyl compounds from alkenes. β-Amino amides and esters, pyrazolidinones, and pyrazolones were accessed by reductive derivatization of the aminocarbonylation products. Exploration into the limits of this reactivity gave insight into fundamental properties of imino-isocyanates. This includes the first detection of imino-isocyanates by IR spectroscopy.
A kinetic resolution of the azomethine imines obtained from this alkene aminocarbonylation reaction was then developed, which gave access to enantioenriched β-amino carbonyl compounds (Chapter 3). This was accomplished by Brønsted acid catalysed reduction, with a selectivity factor of 13-43. This was the first example of the enantioselective reduction of azomethine imines, and represents a new activation mode for reactions of N,N’-cyclic azomethine imines. Using this reductive method, both enantiomers of the β-amino amide could be obtained from a racemic azomethine imine in ≥ 97% ee.
The discovery of new reactivity of imino-isocyanates with imines in described in Chapter 4, which allowed the synthesis of eight new azomethine imines with the triazolone core. Our initial scope studies revealed different trends with imines than with alkenes, including increased reactivity, which led to investigation of the mechanism of this reaction. In addition, this was shown to be a valuable new approach for the synthesis of triazolones from imines.
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APPLICATIONS OF ENANTIOPURE SULFINIMINE DERIVED CHIRAL AMINE BUILDING BLOCKS FOR THE ASYMMETRIC SYNTHESIS OF TROPANE ALKALOIDS AND CYCLIC CIS BETA-AMINO ACID DERIVATIVESTheddu, Naresh January 2011 (has links)
Chiral amines are ubiquitous in natural products and are found in many drugs and drug candidates. Enantiopure sulfinimines [RS(O)N=CHR1] are useful chiral building blocks for the stereoselective synthesis of amines and amine derivatives. The aim of this thesis research is to develop new methods to access chiral amine building blocks for applications in the synthesis of nitrogen-heterocycles including ring-substituted tropinones, tropanes, cyclic cis-beta-amino acid derivatives, and amino-cyclopentitols. / Chemistry
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Cycloaddition [3+2] de cétènes avec des aziridines / [3+2] cycloaddition of ketenes with aziridinesViceriat, Audrey 03 December 2015 (has links)
Ce travail de thèse a permis de développer un nouveau type de cycloaddition [3+2] des cétènes impliquant des aziridines. Les aziridines sont de bons précurseurs de dipôles 1,3-azotés zwittérioniques, via la coupure sélective de leur liaison C-N par activation avec un acide de Lewis. Nous avons montré qu'en présence d'un cétène et d'iodure de lithium, l'aziridine s'ouvre, et le dipôle 1,3 formé réagit avec le cétène pour offrir des gamma-lactames de manière très efficace. Cette nouvelle cycloaddition [3+2] s'étend à la transformation monotope d'une imine en gamma-lactame, stratégie compatible avec une large gamme d'imines aromatiques et de cétènes stables. Enfin, une synthèse monotope, catalytique et asymétrique de gamma-lactames énantioenrichis a été développée à partir d'oléfines par aziridination asymétrique avec des nitrènes. / This thesis work focuses on a new type of [3+2] cycloaddition of ketenes with aziridines. Aziridines are good precursors of zwitterionic 1,3-aza-dipoles, by selective C-N bond cleavage catalyzed by Lewis acid. We have found that ketenes react with the 1,3-dipole generated by addition of lithium iodide to the aziridine, efficiently providing the gamma-lactams. This new cycloaddition could be extended to a one-pot simple transformation of imines to gamma-lactams. The synthesis is compatible with a wide range of aromatic imines and stable ketenes. Finally, a one-pot catalytic asymmetric synthesis of enantioenrichied gamma-lactams have been developed starting from olefins, involving an asymmetric nitrene aziridination.
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Nitrene Transfer Reactions Mediated by Transition Metal Scorpionate ComplexesLiang, Shengwen 11 September 2012 (has links)
No description available.
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Nouvel accès chimio-, régio- et stéréosélectif aux motifs spirolactones polycycliques via une réaction de cycloaddition [3+2] / New chemo-, regio- and stereoselective access to polycyclic spirolactone residue via a [3+2] cycloadditionRodier, Fabien 16 November 2012 (has links)
Le système spirocyclique (7,5) est un motif récurrent dans un certain nombre de produits naturels tels que les Micrandilactones ou les Rubriflordilactones. Ces structures polycycliques représentent un réel défi synthétique pour les chimistes organiciens puisqu'elles présentent au moins neuf centres stéréogènes dont plusieurs sont quaternaires. L'objectif principal de ce travail était de développer de nouvelles réactions de cycloaddition [3+2] et de les utiliser comme étape clé afin d'obtenir rapidement et efficacement le squelette polycylique de ces composés. La première partie de ces travaux a été consacrée au développement d'une réaction de cycloaddition [3+2] intra- et intermoléculaire mettant un jeu un nouveau partenaire dipolarophile, les γ-alkylidènes-buténolides. Cette étape clé conduit à la formation de cycloadduits hautement fonctionnalisés de façon rapide et efficace avec d'excellents rendements et de façon hautement chimio-, régio- et diastéréosélective. De plus, des calculs théoriques ont permis d'appréhender le mécanisme réactionnel entre un 2-diazo-1,3-cétoester et la protoanémonine catalysé par un sel de rhodium mis en jeu dans ce type de processus et ainsi d'expliquer les résultats obtenus.Dans une deuxième partie, deux approches aux cœurs ABC et CD de la micrandilactone C ont été développées mettant respectivement en jeu une cycloaddition [3+2] formellement intermoléculaire utilisant un lien de type acétal de silicium et suivie par une réaction de Diels Alder. Ainsi, le motif tétracyclique devrait être rapidement accessible après quelques aménagements de la voie de synthèse initiale. / The spiro (7, 5) ring system is a recurring structural moiety in numerous natural products such as Micrandilactones and Rubriflordilactones. In term of complexity, these polycyclic structures represent a synthetic challenge for organic chemist. Indeed, these molecules present at least nine stereogenic centres including several quaternary ones. The main goal of this work was to use unprecedented partners in the [3+2] cycloaddition reaction to obtain quickly and efficiently the polycyclic core of those natural products. The first part of these studies was dedicated to the development of an intra- and intermolecular [3+2] cycloaddition using for the first time a γ-alkylidene-butenolide dipolarophile. This approach provides rapid and facile access to highly functionalised polycyclic molecules along with excellent regio-, chemo- and stereoselectivities. In addition, thanks to computational studies an overall picture of the mechanism of the intermolecular rhodium catalysed [3+2] cycloaddition between 2-diazo-1,3-ketoester and protoanemonin was apprehended, and experimental results have been rationalised.Finally, two approaches to the ABC and CD cores of Micrandilactone C were developed using respectively a formal intermolecular [3+2] cycloaddition reaction in presence of a silicon acetal linker followed by a Diels Alder reaction. The ACDE tetracyclic moiety should be quickly accessible after few modifications of the initial strategy.
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1,3-Dipolare Cycloaddition von N2O an hochreaktive MehrfachbindungenPlefka, Oliver 20 July 2011 (has links) (PDF)
In der vorliegenden Arbeit wird über 1,3-dipolare Cycloadditionen mit Lachgas (N2O) unter milden Reaktionstemperaturen (≈ RT) berichtet.
N2O ist ein sehr unreaktives 1,3-dipolares Reagenz. Bisher in der Literatur durchgeführte 1,3-dipolare Cycloadditionen mit N2O benötigten immer sehr drastische und gefährliche Reaktionsbedingungen (bis zu 300°C und 500 atm.). Dabei entstanden nach einer (postulierten) einleitenden 1,3-dipolaren Cycloaddition von N2O an Olefine oder Alkine immer nur stickstofffreie Reaktionsprodukte.
Durch den Einsatz von hochreaktiven Cycloalkinen als 1,3-Dipolarophile konnten erstmals 1,3-dipolare Cycloadditionen mit N2O bei deutlich milderen Bedingungen (–25°C bis +60°C) als den bisher bekannten durchgeführt werden. Dabei war es mit Cyclooctin und Cycloocten-5-in erstmals möglich, stabile und vollständig charakterisierbare Reaktionsprodukte zu erhalten, die alle drei Atome des addierten N2O-Moleküls enthalten. Mit 4,5-Didehydro-2,3,6,7-tetrahydro-3,3,6,6-tetramethylthiepin konnte sogar erstmals ein alpha-Diazoketon durch 1,3-dipolare Cycloaddition von N2O erhalten und dieses bei –25°C NMR-spektroskopisch untersucht werden.
Diese alpha-Diazoketone entstehen aus der elektrocyclischen Ringöffnung der entsprechenden 1,2,3-Oxadiazole welche aus der Cycloaddition von N2O und dem eingesetzten Cycloalkin stammen.
Mit alpha-substituierten Cyclooctinen konnten auch 1,3-dipolare Cycloadditionen mit N2O bei milden Temperaturen durchgeführt werden, um stickstofffreie Reaktionsprodukte zu erhalten.
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1,3-Dipolare Cycloaddition von N2O an hochreaktive MehrfachbindungenPlefka, Oliver 16 June 2011 (has links)
In der vorliegenden Arbeit wird über 1,3-dipolare Cycloadditionen mit Lachgas (N2O) unter milden Reaktionstemperaturen (≈ RT) berichtet.
N2O ist ein sehr unreaktives 1,3-dipolares Reagenz. Bisher in der Literatur durchgeführte 1,3-dipolare Cycloadditionen mit N2O benötigten immer sehr drastische und gefährliche Reaktionsbedingungen (bis zu 300°C und 500 atm.). Dabei entstanden nach einer (postulierten) einleitenden 1,3-dipolaren Cycloaddition von N2O an Olefine oder Alkine immer nur stickstofffreie Reaktionsprodukte.
Durch den Einsatz von hochreaktiven Cycloalkinen als 1,3-Dipolarophile konnten erstmals 1,3-dipolare Cycloadditionen mit N2O bei deutlich milderen Bedingungen (–25°C bis +60°C) als den bisher bekannten durchgeführt werden. Dabei war es mit Cyclooctin und Cycloocten-5-in erstmals möglich, stabile und vollständig charakterisierbare Reaktionsprodukte zu erhalten, die alle drei Atome des addierten N2O-Moleküls enthalten. Mit 4,5-Didehydro-2,3,6,7-tetrahydro-3,3,6,6-tetramethylthiepin konnte sogar erstmals ein alpha-Diazoketon durch 1,3-dipolare Cycloaddition von N2O erhalten und dieses bei –25°C NMR-spektroskopisch untersucht werden.
Diese alpha-Diazoketone entstehen aus der elektrocyclischen Ringöffnung der entsprechenden 1,2,3-Oxadiazole welche aus der Cycloaddition von N2O und dem eingesetzten Cycloalkin stammen.
Mit alpha-substituierten Cyclooctinen konnten auch 1,3-dipolare Cycloadditionen mit N2O bei milden Temperaturen durchgeführt werden, um stickstofffreie Reaktionsprodukte zu erhalten.
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