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Maxence Valla James W. Harris Rajamani Gounder William N. P. van der Graaff Evgeny A. Pidko Emiel J. M. Hensen Paola Ferrini Jan Dijkmans Bert Sels Ive Hermans Christophe Copéret 《Helvetica chimica acta》2016,99(12):916-927
In recent years, various protocols on preparing Lewis acidic Sn‐β zeolite hydrothermally and postsynthetically have been reported. However, very little is known about the effects of different synthesis protocols on the Sn(IV) speciation in the final material. Even the effects of individual synthesis parameters within a certain preparation method have not been studied systematically. Here, we demonstrate that hydrothermally synthesized Sn‐β zeolites prepared via very similar recipes show significantly different 119Sn‐NMR spectra, suggesting different Sn site speciation. Among postsynthetically prepared Sn‐β zeolites, less variation in the resulting 119Sn‐NMR spectra have been observed, indicating a more reproducible synthesis procedure compared to hydrothermal synthesis in fluoride media. This work highlights the importance of 119Sn‐NMR measurements to elucidate the precise local geometry of the Sn heteroatoms in Sn‐β, and the need to quantify the number of reactive Sn sites on each sample that participate in a given catalytic reaction, in order to accurately compare materials prepared by different routes. 相似文献
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Computational SN2‐Type Mechanism for the Difluoromethylation of Lithium Enolate with Fluoroform through Bimetallic C−F Bond Dual Activation
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Kazuya Honda Dr. Travis V. Harris Dr. Miho Hatanaka Prof. Dr. Keiji Morokuma Prof. Dr. Koichi Mikami 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(26):8796-8800
The reaction mechanism for difluoromethylation of lithium enolates with fluoroform was analyzed computationally (DFT calculations with the artificial force induced reaction (AFIR) method and solvation model based on density (SMD) solvation model (THF)), showing an SN2‐type carbon–carbon bond formation; the “bimetallic” lithium enolate and lithium trifluoromethyl carbenoid exert the C?F bond “dual” activation, in contrast to the monometallic butterfly‐shaped carbenoid in the Simmons–Smith reaction. Lithium enolates, generated by the reaction of 2 equiv. of lithium hexamethyldisilazide (rather than 1 or 3 equiv.) with the cheap difluoromethylating species fluoroform, are the most useful alkali metal intermediates for the synthesis of pharmaceutically important α‐difluoromethylated carbonyl products. 相似文献
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Nadiia Kovalenko Dr. Jonathan A. Swain Georgina K. Howard Yann O. Hermant Dr. Alan J. Cameron Dr. Louise A. Stubbing Prof. Paul W. R. Harris Prof. Margaret A. Brimble 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202554
In the current global crisis of antimicrobial resistance, antimicrobial peptides represent a promising source of alternative antibiotics. Recently discovered cadaside B, a novel calcium-dependent antibiotic, exhibits potent antimicrobial activity towards Gram-positive pathogens including multi-drug resistant strains. These properties, coupled with a novel structure, non-cytotoxicity, and low likelihood of developing resistance render cadaside B an important synthetic target. Herein, a synthetic strategy towards cadaside B is reported with the key steps involving on-resin depsipeptide bond formation and solution-phase macrolactamization. Good agreement of the synthetic cadaside B MS/MS fragmentation pattern was observed with the natural product, but a different 1H NMR spectrum and absence of antimicrobial activity suggest an undetected epimerization event took place during the synthesis. Herein the findings of our synthetic journey and suggestions for future directions are presented. 相似文献
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Thomas Osborne und Isaak F. Harris 《Fresenius' Journal of Analytical Chemistry》1904,43(6-7):378-382
Ohne ZusammenfassungNach einem gefälligst zugesandten Abdruck aus dem Journal of the American Chemical Society25, No. 8, übersetzt und bearbeitet von Dr. Griessmayer. 相似文献