1,720,953 research outputs found
Allylic Functionalization Reactions Enabled by Photoinduced Radical Generation of Π-allylpalladium
No full textThis thesis describes two photocatalytic radical strategies for accessing π-allyl Pd(II) complexes
and the transformations thereof. In the first approach, a photoexcited Pd(0) catalyst engages alkyl
iodides in a single electron transfer event, producing alkyl radicals that undergo radical addition
to conjugated dienes to generate hybrid allyl Pd(I) radicals. These open-shell species can then
collapse into electrophilic π-allyl Pd(II) intermediates via radical–polar crossover. Subsequent
interception by external nucleophiles, such as amines, phenols, and malonates, through Tsuji–
Trost-type mechanism yields a range of carbofunctionalization products. This work represents one
of the early examples of alkene difunctionalization in palladium photocatalysis. The second
strategy involves generating hybrid allyl Pd(I) radicals by homolytically activating the allylic C–
H bonds of alkenes via hydrogen atom transfer to aryl radicals, which are similarly derived from
aryl bromides under photocatalytic conditions. Likewise, radical–polar crossover furnishes
classical π-allyl Pd(II) complexes, which upon nucleophilic attack by external nucleophiles afford
allylic C–H functionalization products. Notably, the aryl bromide serves as an oxidant in this
process, which is unconventional given their well-established role as cross-coupling partners in
transition metal catalysis. Furthermore, employing a chiral ligand renders the transformation
stereoselective, representing the first instance of asymmetric palladium photocatalysis. This
radical-based strategy provides new mechanisms for intermolecular C(sp3)–H functionalization
with the potential to complement current technologies or address their limitations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Copper(I)-catalyzed interrupted click reaction with TMSCF3: synthesis of 5-trifluoromethyl 1,2,3-triazoles
No full textM.Phil.The first part of this thesis details a copper(I)-catalyzed interrupted click reaction for the synthesis of 5-trifluoromethyl 1,2,3-triazoles. This work has recently been published (Cheung, K. P. S.; Tsui, G. C. Org. Lett. 2017, 19, 2881).Since its initial discovery, the click reaction has become a premier reaction to access 1,4-disubstituted 1,2,3-triazoles from terminal alkynes and organic azides. To synthesize fully substituted triazoles, the interrupted click reaction is the most direct and efficient approach in which a third reaction partner is added.On the other hand, incorporation of a trifluoromethyl group can significantly increase the pharmacological properties of an organic molecule. Given the extensive applications of 1,2,3-triazoles in medicinal and pharmaceutical chemistry, the 5-trifluoromethyl 1,2,3-triazole could be an important addition to the current library.However, literature approaches involve the use of CF3-building blocks or prefunctionalized triazoles, which are tedious to prepare and require multiple steps to synthesize. Herein, a new protocol for the one-step synthesis of 5-trifluoromethyl 1,2,3-triazoles from readily available terminal alkynes, organic azides and (trifluoromethyl)trimethylsilane (TMSCF3) is described. This three-component reaction demonstrates a high functional group tolerability in both alkynes and azides,allowing for the modular synthesis of various trifluoromethylated 1,2,3-triazoles with complete regioselectivity. The application of this protocol is also demonstrated by the expedient synthesis of the drug analogue of rufinamide. Control experiments support the mechanism in which the catalytic cycle is intercepted by TMSCF3 under an oxidative condition.The second part of this thesis describes the preliminary exploration of a regiodivergent boron-copper addition to trifluoromethylated alkenes.Asymmetric copper-catalyzed borylation of alkenes has become an important method for the synthesis of enantioenriched boron-containing compounds, which are valuable synthons for further transformations such as arylation and amination. While bis(pinacolato)diboron has been extensively used, ligand-controlled regiodivergent boron-copper addition remained underexplored. On the other hand, seldom are trifluoromethylated alkenes used in borylation reactions. We therefore became interested to develop protocols that deliver a- and b-borylated products selectively fromtrifluoromethylated alkenes. Through screening of different types of ligands, our preliminary results showed that ligand can indeed control the regio-outcome of the borylation products. Further exploration is ongoing in our laboratory.本論文第一部分詳細描述銅(I)催化的Interrupted Click 反應，以此合成5-三氟甲基 1,2,3-三唑。自從被發現以來，Click反應已成為通過末端炔烴和有機疊氮來製備1,4-二取代1,2,3-三唑的主要反應。而要合成全取代的三唑，加入第三個反應組份的Interrupted Click 反應是最直接和有效的方法。另一方面，引入三氟甲基可顯著改善有機分子的藥理學性質。鑑於1,2,3-三唑在醫藥和藥物化學中的廣泛應用，5-三氟甲基1,2,3-三唑具有成為藥物的潛在價值，然而此類三唑的文獻合成方法主要使用CF3模塊或預官能化的三唑，其製備方法一般需要多個步驟。在此，我們描述一個使用易獲取的末端炔烴、有機疊氮和三氟甲基三甲基矽烷(TMSCF3)一步合成5-三氟甲基1,2,3-三唑的新方法。這個三組份反應在炔烴和疊氮中顯示出高官能團耐受性，允許以組合化學方式來合成具有完全區域選擇性的各種三氟甲基化1,2,3-三唑。這個方法也被應用到rufinamide的藥物類似物的高效合成。對照實驗支持在氧化條件下TMSCF3 參與催化循環的機理。本論文第二部分探討三氟甲基化烯烴的區域多樣性硼銅加成反應。銅催化的烯烴不對稱硼化已成為合成手性硼化合物的重要方法。硼化合物可用於進一步轉化為有價值的芳基和胺基化合物。雖然雙（頻哪醇合）二硼已被廣泛使用，但配體控制的區域多樣性硼銅加成仍然未被深入研究。另一方面，三氟甲基取代烯烴很少應用於硼化反應。鑑於此，三氟甲基取代烯烴的a-和b-選擇性硼化吸引了我們的注意。初步的實驗結果顯示配體可以控制硼化產物的區域選擇性。進一步的研究正在進行中。Cheung, Pak Shing.TMSCF3, 3 in title is subscript.Thesis M.Phil. Chinese University of Hong Kong 2018.Includes bibliographical references.Abstracts also in Chinese.Title from PDF title page (viewed on 21, August, 2020)
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