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991.
A General Strategy for the Catalytic,Highly Enantio‐ and Diastereoselective Synthesis of Indolizidine‐Based Alkaloids
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Falko Abels Chris Lindemann Prof. Dr. Christoph Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(7):1964-1979
Sixteen indolizidine‐based alkaloids (IBAs) that were isolated as poison constituents of the skin of frogs were synthesized in a highly flexible and stereoselective manner. As a key step, a three‐component, organocatalytic, highly enantio‐ and diastereoselective vinylogous Mukaiyama–Mannich reaction was employed furnishing optically highly enriched butyrolactams as central intermediates on a multigram scale. The attached six‐membered ring was constructed through cyclization of the pendant enoate moiety onto the pyrrolidine ring. The absolute configuration of the bridgehead chiral center and the adjacent 8‐position was established in the initial vinylogous Mannich reaction, whereas the 3‐ and 5‐substituents were introduced through organometallic addition at a late stage of the synthesis with full stereochemical control from the substrate. With this strategy, simple as well as even more complex alkaloids were accessible in good overall yields as single stereoisomers. These syntheses also served to establish the absolute and relative configuration of those IBAs that had never been synthesized before. 相似文献
992.
van den Berg Jan Bouwe Groothedde Chris Lessard Jean-Philippe 《Journal of Dynamics and Differential Equations》2022,34(2):853-896
Journal of Dynamics and Differential Equations - In this paper we develop a general computer-assisted proof method for periodic solutions to delay differential equations. The class of problems... 相似文献
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The structure of citorellamine, isolated from the tunicate , has been deduced from spectroscopic analyses and chemical transformations. 相似文献
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Kai Wing Cheng Chris S. C. Mak Wai Kin Chan Alan Man Ching Ng Aleksandra B. Djurišić 《Journal of polymer science. Part A, Polymer chemistry》2008,46(4):1305-1317
Two conjugated polymers based on poly(phenylenethiophene) and poly (fluorenethiophene) main chain functionalized with pendant trithiocyanato ruthenium terpyridine complexes were synthesized by the Suzuki coupling reaction. The ruthenium complexes can extend the absorption band to longer wavelength and enhance the photosensitivity in this region. The polymers exhibit very broad absorption band spanning from 400 to 750 nm due to the presence of π‐conjugated system and the ruthenium complexes. Such enhancement in optical absorption enables the utilization of solar light in the near IR region. By space charge limited current modeling, the hole carrier mobilities of the polymers were calculated to be in the order of 10?4 cm2 V?1 s?1, which greatly facilitate the transport of charges after the separation of excitons. Heterojunction photovoltaic cells with simple structure ITO/polymer/C60/Al were fabricated. Under simulated AM1.5 solar light illumination, the short circuit currents, open circuit voltages, and power conversion efficiencies of the photovoltaic cells were measured to be 1.53–2.58 mA cm?2, 0.12–0.24 V, and 0.084–0.12%, respectively. Deposition of PEDOT:PSS on ITO surface did not show significant difference in device performance. Plot of incident photon to charge efficiency as the function of wavelength suggests that absorption by both conjugated main chain and ruthenium complex are essential to the photocurrent generation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1305–1317, 2008 相似文献
998.
Igor Linkov Jeffery Steevens Gitanjali Adlakha-Hutcheon Erin Bennett Mark Chappell Vicki Colvin J. Michael Davis Thomas Davis Alison Elder Steffen Foss Hansen Pertti Bert Hakkinen Saber M. Hussain Delara Karkan Rafi Korenstein Iseult Lynch Chris Metcalfe Abou Bakr Ramadan F. Kyle Satterstrom 《Journal of nanoparticle research》2009,11(3):513-527
Nanomaterials and their associated technologies hold promising opportunities for the development of new materials and applications
in a wide variety of disciplines, including medicine, environmental remediation, waste treatment, and energy conservation.
However, current information regarding the environmental effects and health risks associated with nanomaterials is limited
and sometimes contradictory. This article summarizes the conclusions of a 2008 NATO workshop designed to evaluate the wide-scale
implications (e.g., benefits, risks, and costs) of the use of nanomaterials on human health and the environment. A unique
feature of this workshop was its interdisciplinary nature and focus on the practical needs of policy decision makers. Workshop
presentations and discussion panels were structured along four main themes: technology and benefits, human health risk, environmental
risk, and policy implications. Four corresponding working groups (WGs) were formed to develop detailed summaries of the state-of-the-science
in their respective areas and to discuss emerging gaps and research needs. The WGs identified gaps between the rapid advances
in the types and applications of nanomaterials and the slower pace of human health and environmental risk science, along with
strategies to reduce the uncertainties associated with calculating these risks. 相似文献
999.
Summary The mass absorption coefficients of some glassy and crystalline silicates of astrophysical relevance have been measured. We
produced and characterized also synthetic silicates of olivine type since this material is considered one of the most likely
components of cometary dust grains. The experimental data are used to fit the emission feature observed in the Comet Halley
spectrum between 8 and 13 μm. Satisfactory results are obtained by using synthetic olivine mixed with a small amount (5%)
of crystalline grains.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献
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