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1	Development of an Elegant, Thermally Benign Johnson-Claisen Rearrangement Kelly Cosgrove Unknown Date (has links) The Johnson-Claisen rearrangement is a valuable method for the formation of new carbon-carbon bonds, however the rearrangement suffers from high reaction temperatures and prolonged reaction times. On the basis of previous research into substituent-induced rate enhancements of the Claisen rearrangement, we aimed to reduce the severity of the Johnson-Claisen conditions by applying this reaction to allylic cyanohydrins. Application of the standard Johnson-Claisen conditions (excess of orthoester and catalytic protic acid) to allylic cyanohydrins resulted in their decomposition to a,b- unsaturated aldehydes. The anticipated d-ethoxycarbonyl-a,b-unsaturated nitriles were formed in trace amounts. Subsequent optimisation of this reaction has allowed a practical entry into a,b- unsaturated nitriles in reasonable yields, however high reaction temperatures were necessary for an efficient conversion. Clearly, a change of approach was desired; we have since discovered that mixed orthoesters derived from allylic alcohols undergo methanol elimination in the presence of triisobutylaluminium (TIBAL) at room temperature to form mixed ketene acetals. TIBAL then promotes immediate Claisen rearrangement of these intermediates, and subsequent reduction of the ester products to yield, g,d- unsaturated primary alcohols in a convenient one-pot procedure, with yields ranging from 52-81% and with a range of functional group tolerance.
2	Cycloaddition (4+1) formelle intermoléculaire entre un carbène libre riche en électrons et des carbonyles α,β-insaturés et transformations de l’orthoester obtenu en furanne et 5H-furanone Croisetière, Jean-Philippe January 2017 (has links) Le premier chapitre traite d’une réaction de cycloaddition (4+1) sur des énones et des énals à l’aide du diméthoxycarbène. Cette méthode permettrait d’obtenir des hétérocycles à cinq membres à partir de substrats linéaires simples et faciles à fabriquer. On retrouve dans ce chapitre l’optimisation de cette étape réactionnelle, ainsi que son utilisation pour préparer une gamme de substrats. Le second chapitre traite de la transformation des hétérocycles obtenus, et décrits au chapitre précédent, en furannes ainsi qu’en furanones. Cette méthode permet la transformation d’énones et d’énals en hétérocycles oxygénés à cinq membres en seulement deux étapes. On retrouve dans ce chapitre la description de plusieurs méthodes développées pour parvenir aux substrats, ainsi que les échecs rencontrés pour l’obtention de benzofuranne. Cycloaddition (4+1) Hétérocycle Orthoester Furanne Furanone Building block Furan Butenolide (4+1)-cycloaddition Heterocycle Buténolide Bloc de construction
3	Synthesis with Perfect Atom Economy: Generation of Furan Derivatives by 1,3-Dipolar Cycloaddition of Acetylenedicarboxylates at Cyclooctynes Banert, Klaus, Bochmann, Sandra, Ihle, Andreas, Plefka, Oliver, Taubert, Florian, Walther, Tina, Korb, Marcus, Rüffer, Tobias, Lang, Heinrich 25 September 2014 (has links) (PDF) Cyclooctyne and cycloocten-5-yne undergo, at room temperature, a 1,3-dipolar cycloaddition with dialkyl acetylenedicarboxylates 1a,b to generate furan-derived short-lived intermediates 2, which can be trapped by two additional equivalents of 1a,b or alternatively by methanol, phenol, water or aldehydes to yield polycyclic products 3b–d, orthoesters 4a–c, ketones 5 or epoxides 6a,b, respectively. Treatment of bis(trimethylsilyl) acetylenedicarboxylate (1c) with cyclooctyne leads to the ketone 7 via retro-Brook rearrangement of the dipolar intermediate 2c. In all cases, the products are formed with perfect atom economy. Technische Universität Chemnitz Publikationsfonds Kaskadenreaktionen Cyclopropene Diels-Alder-Reaktionen dipolare Zwischenstufen Epoxide Orthoester Sauerstoffheterocyclen Reaktionsmechanismen Retro-Brook-Reaktionen gespannte Verbindungen cascade reactions cyclopropenes Diels-Alder reactions dipolar intermediates epoxides orthoesters oxygen heterocycles reaction mechanisms retro-Brook reactions strained compounds Technische Universität Chemnitz Publication funds ddc:540 Epoxide Ortho-Ester Sauerstoffheterocyclen
4	Synthesis with Perfect Atom Economy: Generation of Furan Derivatives by 1,3-Dipolar Cycloaddition of Acetylenedicarboxylates at Cyclooctynes Banert, Klaus, Bochmann, Sandra, Ihle, Andreas, Plefka, Oliver, Taubert, Florian, Walther, Tina, Korb, Marcus, Rüffer, Tobias, Lang, Heinrich 25 September 2014 (has links) Cyclooctyne and cycloocten-5-yne undergo, at room temperature, a 1,3-dipolar cycloaddition with dialkyl acetylenedicarboxylates 1a,b to generate furan-derived short-lived intermediates 2, which can be trapped by two additional equivalents of 1a,b or alternatively by methanol, phenol, water or aldehydes to yield polycyclic products 3b–d, orthoesters 4a–c, ketones 5 or epoxides 6a,b, respectively. Treatment of bis(trimethylsilyl) acetylenedicarboxylate (1c) with cyclooctyne leads to the ketone 7 via retro-Brook rearrangement of the dipolar intermediate 2c. In all cases, the products are formed with perfect atom economy. info:eu-repo/classification/ddc/540 ddc:540

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