Mechanism and Enantioselectivity in Palladium-Catalyzed Conjugate Addition of Arylboronic Acids to β‑Substituted Cyclic Enones: Insights from Computation and Experiment

Enantioselective conjugate additions of arylboronic acids to β-substituted cyclic enones have been previously reported from our laboratories. Air- and moisture-tolerant conditions were achieved with a catalyst derived in situ from palladium(II) trifluoroacetate and the chiral ligand (S)-t-BuPyOx. We now report a combined experimental and computational investigation on the mechanism, the nature of the active catalyst, the origins of the enantioselectivity, and the stereoelectronic effects of the ligand and the substrates of this transformation. Enantioselectivity is controlled primarily by steric repulsions between the t-Bu group of the chiral ligand and the α-methylene hydrogens of the enone substrate in the enantiodetermining carbopalladation step. Computations indicate that the reaction occurs via formation of a cationic arylpalladium(II) species, and subsequent carbopalladation of the enone olefin forms the key carbon–carbon bond. Studies of nonlinear effects and stoichiometric and catalytic reactions of isolated (PyOx)Pd(Ph)I complexes show that a monomeric arylpalladium–ligand complex is the active species in the selectivity-determining step. The addition of water and ammonium hexafluorophosphate synergistically increases the rate of the reaction, corroborating the hypothesis that a cationic palladium species is involved in the reaction pathway. These additives also allow the reaction to be performed at 40 °C and facilitate an expanded substrate scope

Netzwerk Teilchenwelt - Jugendliche und Lehrkräfte erfahren aktuelle Forschung

Das bundesweit agierende Netzwerk Teilchenwelt ist ein Netzwerk zur Förderung von Teilchenphysik in der Gesellschaft. Hierbei werden vor allem Jugendliche und Lehrkräfte angesprochen, die anhand zweier authentischer Projekte lernen können, wie (Astro-)Teilchenphysiker Erkenntnisse gewinnen. Neben den bereits etablierten Teilchenphysik Masterclasses, können die Zielgruppen im Cosmic Projekt mehr über die Messung von kosmischen Teilchen lernen. Im folgenden Beitrag werden neben dem Format des Projekts auch beide Experimente und mögliche Messungen detaillierter vorgestellt. Weiterhin wird auf die Evaluation der Wirksamkeit der Veranstaltungen eingegangen. Hierbei soll untersucht werden inwiefern eine physikbezogene Interessensteigerung durch das Cosmic Projekt hervorgerufen werden kann. Ebenfalls soll ein Vergleich zwischen den Durchführungen in außerschulischen Lernorten und dem Lernort Schule gezogen werden

Cu-catalyzed formation of triazole-linked glycoamino acids and application in chemoenzymatic peptide synthesis

Item does not contain fulltext9 p

Enantioselective Synthesis of Tertiary Alcohols through a Zirconium-Catalized Friedel-Crafts Alkylation of Pyrroles with alpha-Ketoesters

Chiral complexes of 1,10-bi-2-naphthol-based ligands with zirconium tert-butoxide catalyze the Friedel Crafts alkylation of pyrroles with R-ketoesters to afford tertiary alcohols in good yields and ee up to 98%. The reaction is also of application to 4,7-dihydroindole to give C2-alkylated indoles after oxidation with p-benzoquinone.We thank the Ministerio de Ciencia e Innovacion and FEDER (Grant CTQ2009-13083) and the Generalitat Valenciana (Grant ACOMP/2011/267) for financial support. C.V. thanks the Generalitat Valenciana for a predoctoral grant.Blay, G.; Fernández, I.; Muñoz Roca, MDC.; Pedro, J.; Recuenco, A.; Vila, C. (2011). Enantioselective Synthesis of Tertiary Alcohols through a Zirconium-Catalized Friedel-Crafts Alkylation of Pyrroles with alpha-Ketoesters. Journal of Organic Chemistry. 76:6286-6294. https://doi.org/10.1021/jo2010704S628662947

Catalytic asymmetric carbon–carbon bond formation via allylic alkylations with organolithium compounds

Carbon–carbon bond formation is the basis for the biogenesis of nature’s essential molecules. Consequently, it lies at the heart of the chemical sciences. Chiral catalysts have been developed for asymmetric C–C bond formation to yield single enantiomers from several organometallic reagents. Remarkably, for extremely reactive organolithium compounds, which are among the most broadly used reagents in chemical synthesis, a general catalytic methodology for enantioselective C–C formation has proven elusive, until now. Here, we report a copper-based chiral catalytic system that allows carbon–carbon bond formation via allylic alkylation with alkyllithium reagents, with extremely high enantioselectivities and able to tolerate several functional groups. We have found that both the solvent used and the structure of the active chiral catalyst are the most critical factors in achieving successful asymmetric catalysis with alkyllithium reagents. The active form of the chiral catalyst has been identified through spectroscopic studies as a diphosphine copper monoalkyl species.