“…Thus, it has been deduced from reactivity data that ruthenium catalysts, in particular complex 1 , respond in a delicate way to chelation by carbonyl groups in vicinity to the olefins. − While some level of Lewis acid/Lewis base interaction seems to be necessary for productive macrocyclization (cf. Scheme ), stable ruthenium chelate complexes must be avoided because they might sequester the catalyst in an unproductive form, as suggested by the data shown in Scheme . , Addition of an appropriate Lewis acid such as Ti(O i Pr) 4 , which competes with the Ru center for the coordination site, may help to rectify such a situation. , 1 2 …”
The ruthenium chelate complexes 4 and 5 were prepared by reaction of the Grubbs catalyst
1 and its second-generation analogue 2 with the 2-vinylbenzoic acid isopropyl ester 3 in the
presence of CuCl. The fact that the chelating carbonyl group in these complexes attenuates
their catalytic activity sets an experimental basis for the interpretation of reactivity data
previously described in the literature.
“…Thus, it has been deduced from reactivity data that ruthenium catalysts, in particular complex 1 , respond in a delicate way to chelation by carbonyl groups in vicinity to the olefins. − While some level of Lewis acid/Lewis base interaction seems to be necessary for productive macrocyclization (cf. Scheme ), stable ruthenium chelate complexes must be avoided because they might sequester the catalyst in an unproductive form, as suggested by the data shown in Scheme . , Addition of an appropriate Lewis acid such as Ti(O i Pr) 4 , which competes with the Ru center for the coordination site, may help to rectify such a situation. , 1 2 …”
The ruthenium chelate complexes 4 and 5 were prepared by reaction of the Grubbs catalyst
1 and its second-generation analogue 2 with the 2-vinylbenzoic acid isopropyl ester 3 in the
presence of CuCl. The fact that the chelating carbonyl group in these complexes attenuates
their catalytic activity sets an experimental basis for the interpretation of reactivity data
previously described in the literature.
“…Diese Reaktionssequenz ist sowohl stufenund atomçkonomischer als bestehende Routen, die typi- Organokatalysierte Eintopf-Reaktionen Angewandte Chemie scherweise lineare Sequenzen mit mehr als neun aufreinigungspflichtigen Schritte enthalten, als auch vollkommen schutzgruppenfrei. [25]…”
Section: Der Aufreinigungsfaktor (P F )unclassified
Die asymmetrische Organokatalyse konnte erfolgreich in vielen mehrstufigen Eintopf‐Sequenzen eingebunden werden und stellt so einen einfachen, hoch stereoselektiven Zugang zu strukturell komplexen Zielmolekülen dar. Der Schlüssel zu diesem Erfolg liegt in der Eigenschaft organokatalysierter Reaktionen, auch in Gegenwart großer Mengen unbeteiligter Reagentien effizient zu verlaufen. Da der Organokatalysator in substöchiometrischen Mengen vorliegt und es sich um ein organisches Molekül handelt, kann man erwarten, dass er sich in nachfolgenden Reaktionen ebenfalls als passiver Zuschauer verhält. In diesem Kurzaufsatz wird ein einfach anzuwendendes Klassifizierungs‐ und Nomenklatursystem vorgestellt, das die systematische und aussagekräftige Beschreibung von Eintopf‐Reaktionen ermöglicht, und ausgewählte Beiträge aus dem Feld der organokatalysierten Eintopf‐Reaktionen werden gemäß diesem System besprochen. Zum Schluss wird ein Ausblick auf zukünftige Entwicklungen gegeben.
Using two catalytic ring closing metatheses as the key events, a short, completely diastereoselective and highly enantioselective access to the molluscicidal sesquiterpenoids ricciocarpin A and ricciocarpin B was achieved. The hitherto unknown absolute configuration of these natural products is unambiguously established.
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