1,720,973 research outputs found
Pummerer chemistry of benzothiophene S-oxides: Metal-free alkylation and arylation of benzothiophenes
No full textFunctionalized benzothiophenes are important constructs found in molecules with wide ranging biological activity and in organic materials. An efficient, metal-free approach to C3 and C2 arylated and alkylated benzothiophenes is summarized in this review. The strategy utilizes synthetically unexplored yet readily accessible benzothiophene S-oxides in an interrupted Pummerer/charge accelerated [3,3]-sigmatropic rearrangement cascade process to regioselectively install aryl, allyl or propargyl groups at C3 of benzothiophenes at the expense of C–H bonds. The intermediate sulfonium salts generated after the interrupted Pummerer reaction lack aromaticity and therefore allow the [3,3]-sigmatropic rearrangement, the key C–C bond-forming event, to occur under mild conditions. In addition, a previously unexplored 1,2-migration of substituents in benzothiophenium salts, generated during the cascade process, can be used to access C2 functionalized benzothiophenes
Metal-free synthesis of benzothiophenes via 2-fold C-H functionalization: direct access to materials-oriented heteroaromatics
Full text linkDue to their ubiquity in nature and frequent use in organic electronic materials, benzothiophenes are highly sought after. Here we set out an unprecedented procedure for the formation of benzothiophenes via the dual vicinal C–H functionalization of arenes that does not require metal catalysis. This one‐pot annulation proceeds through an interrupted Pummerer reaction/[3,3]‐sigmatropic rearrangement/cyclization sequence to deliver various benzothiophene products. The procedure is particularly effective for the rapid synthesis of benzothiophenes from non‐prefunctionalized polyaromatic hydrocarbons (PAHs).<br/
Enantioselective and Regioselective Copper-Catalyzed Borocyanation of 1-Aryl-1,3-Butadienes
Full text linkA multicomponent copper-catalyzed enantio- and regioselective borocyanation of 1-aryl-1,3-butadienes has been developed. The method provides access to functionalized allylic nitriles in up to 90% yield and 94% ee and thus overcomes some of the long-standing problems associated with the enantioselective insertion of cyano groups into unsaturated organic molecules. Both boron and cyano functionalities can be used as handles for selective manipulation
Transition-Metal-Free Synthesis of C3-Arylated Benzofurans from Benzothiophenes and Phenols
Full text linkWe report a transition metal-free synthesis of benzofurans from benzothiophenes and phenols that exploits the unique reactivity of sulfoxides. Through a sequence involving an interrupted Pummerer reaction and [3,3] sigmatropic rearrangement, phenols can be combined with readily accessible yet synthetically unexplored benzothiophene S-oxides to provide C3- arylated benzofuran products. The products from this approach can undergo subsequent functionalization to gain access to a range of important benzofuran derivatives
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
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