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641.
Dr. Daniel M. Wanner Patrick M. Becker Simon Suhr Dr. Nick Wannenmacher Dr. Slava Ziegler Justin Herrmann Dr. Felix Willig Julia Gabler Khushbu Jangid Dr. Juliane Schmid Andreas C. Hans Dr. Wolfgang Frey Prof. Dr. Biprajit Sarkar Prof. Dr. Johannes Kästner Prof. Dr. René Peters 《Angewandte Chemie (International ed. in English)》2023,62(36):e202307317
Pyrazolones represent an important structural motif in active pharmaceutical ingredients. Their asymmetric synthesis is thus widely studied. Still, a generally highly enantio- and diastereoselective 1,4-addition to nitroolefins providing products with adjacent stereocenters is elusive. In this article, a new polyfunctional CuII-1,2,3-triazolium-aryloxide catalyst is presented which enables this reaction type with high stereocontrol. DFT studies revealed that the triazolium stabilizes the transition state by hydrogen bonding between C(5)−H and the nitroolefin and verify a cooperative mode of activation. Moreover, they show that the catalyst adopts a rigid chiral cage/pore structure by intramolecular hydrogen bonding, by which stereocontrol is achieved. Control catalyst systems confirm the crucial role of the triazolium, aryloxide and CuII, requiring a sophisticated structural orchestration for high efficiency. The addition products were used to form pyrazolidinones by chemoselective C=N reduction. These heterocycles are shown to be valuable precursors toward β,γ’-diaminoamides by chemoselective nitro and N−N bond reductions. Morphological profiling using the Cell painting assay identified biological activities for the pyrazolidinones and suggest modulation of DNA synthesis as a potential mode of action. One product showed biological similarity to Camptothecin, a lead structure for cancer therapy. 相似文献
642.
A comparative study in the framework of large deformations has been conducted to get insight into micro mechanical response of particulate polymeric composites. The propound model enables finite element predictions of displacement response and resulting debonding of a three-phase material subjected to incremental loading conditions. Predictions employ a unit cell of certain shape under specified loading and constraints. The proposed model involves nonlinear material properties and incorporates a strong or weak non-homogeneous interphase region. The interphase toughness is expressed in terms of the adhesion efficiency between the filler and the matrix, though contact conditions are preserved utilizing special contact elements. Interfacial nonlinear spring joint elements regulate debonding initialization, in relation to the imposed failure criterion. Numerical results are presented and discussed for axial tensile and compressive loadings for a variety of values of the imposed parameters. 相似文献
643.
Wiebke Wunderlich Nick Benfaremo Markus Klapper Klaus Müllen 《Macromolecular rapid communications》1996,17(6):433-438
Bulk polymerizations of methyl methacrylate (MMA) at 60°C initiated with 2,2′-azoisobutyronitrile are influenced by the presence of an organic π-donor such as tetrathiafulvalene (TTF). Upon addition of TTF, the ratio of weight- to number-average molecular weights M̄w/M̄n are significantly reduced and the thermal stability of the poly(methyl methacrylate) samples is increased. Kinetic investigations indicate that TTF acts as a retarder on the polymerization mechanism. 相似文献