212 research outputs found
Alkylwanderungen bei Sextettumlagerungen
Die Wanderungstendenzen von Alkylgruppen bei der Beckmann- Criegee- und Isonitril-Nitril-Umlagerung werden untersucht. Aus den relativen Reaktionsgeschwindigkeiten der substituierten Benzylreste werden RĂŒckschlĂŒsse auf die Ladungsverteilung im Ăbergangszustand dieser Reaktionen gezogen und aus dem VerhĂ€ltnis der Wanderungstendenzen des exo und endo- 2- Norbornylrestes auf die Geometrie der wandernden Gruppe im Ăbergangszustand. Der in verschiedenen Sextettumlagerungen unterschiedliche EinfluĂ der -Methylverzweigung in der wandernden Gruppe wird interpretiert
Cobalt-Impregnated Magnetite as General Heterogeneous Catalyst for the Hydroacylation Reaction of Azodicarboxylates
Catalysts consisting of cobalt and nickel impregnated on magnetite have been prepared, characterized and used for the hydroacylation reaction of different azodicarboxylate compounds with aldehydes, using nearly stoichiometric amounts of both reagents in only 3 h. Furthermore, this reaction has been conducted with the smallest amount of catalyst. The cobalt catalyst is stable enough to be removed by magnetic decantation and recycled ten-fold without any detrimental effect on the results.This work was supported by the Spanish Ministerio de EconomĂa y Competitividad (MICINN; CTQ2011-24151) and University of Alicante. J. M.P. thanks the MICINN (FPI program) for her fellowship
Quinones as dienophiles in the Diels-Alder reaction: history and applications in total synthesis
In the canon of reactions available to the organic chemist engaged in total synthesis, the DielsâAlder reaction is among the most powerful and well understood. Its ability to rapidly generate molecular complexity through the simultaneous formation of two carboncarbon bonds is almost unrivalled, and this is reflected in the great number of reported applications of this reaction. Historically, the use of quinones as dienophiles is highly significant, being the very first example investigated by Diels and Alder. Herein, we review the application of the DielsâAlder reaction of quinones in the total synthesis of natural products. The highlighted examples span some 60â
years from the landmark syntheses of morphine (1952) and reserpine (1956) by Gates and Woodward, respectively, through to the present day examples, such as the tetracyclines
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