1,720,959 research outputs found
Developments in the synthesis of polyfunctionalized heteroaromatic systems and applications in asymmetric catalysis
No full textHeterocycles are an important class of organic compounds, due to their occurrence in almost all the biological macromolecules. For this reason, the large majority of pharmaceuticals are synthetic heterocycles which have found widespread use as anticancer agents, analeptics, analgesics, hypnotics, and vasopressor modifiers. Other heterocycles serve as pesticides, insecticides, herbicides, and rodenticides. As result, more than 90% of new drugs contain heterocycles. Other applications include dyestuffs, copolymers, solvents, photographic sensitizers and developers, and antioxidants and vulcanization accelerators in the rubber industry. \ud
The aim of this work is to provide a contribution to the vast area of heterocyclic chemistry. It could be divided in two parts: in the first one new strategies for the synthesis of heteroaromatic-containing compounds are proposed. In the second part, some applications of heterocyclic compounds in organic asymmetric synthesis have been identified.\ud
For the construction of substituted heterocycles, the ability of CeCl3 to promote carbon-heteroatom bond-forming has been exploited. Recent studies in our laboratories have shown that commercially available reagents such as CeCl3.7H2O can be used without any special caution, and its activity increases dramatically in the presence of an iodide source, such as NaI or CuI, resulting in shorter reaction times, diminished byproduct formation, and improved yields and purity of products. \ud
It is very well known that microwave irradiation can shorten the reaction time of many organic reactions and it is a convenient method to promote rapid reactions with much less energy. During our investigation we discovered that the long time (in order of days) of reactions in thermal conditions, are reduced at few hours by employing microwave-assisted procedure. Besides, higher yields may be possible increasing the rate of reactions by effect of microwave irradiation.\u
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
Efficient One-pot Catalyst in the Construction of 2-Substituted Benzimidazoles: Synthesis of Benzimidazo[1,2-c]quinazolines
No full textThe benzimidazole core is a common moiety in a large number of natural products and pharmacologically active small molecules. The synthesis of novel benzimidazole derivatives remains a main focus in medicinal research. In continuation of the efforts towards Ce(III) catalysts for organic transformations, we observed for the first time the activity of the iodide ion and copper cation in activating CeCl3·7H2O in the selective formation of prototypical 2-substituted benzimidazoles. The one-pot CeCl3·7H2O–CuI catalytic system procedure includes the cyclo-dehydrogenation of aniline Schiff’s bases, generated in situ from the condensation of 1,2-phenylenediamine and aldehydes, followed by the oxidation with iodine, which works as a hydrogen sponge. Mild reaction conditions, good to excellent yields, and clean reactions make the procedure a useful contribution to the synthesis of biologically active fused heterocycles containing benzimidazoquinazolines.
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
Influence of Cerium (III) Cation of the Witting Olefination
No full textThe Wittig reaction is probably the most widely recognized method for the carbonyl olefination, mainly thanks to the certainty with wich the position of the newly formed double bond can be established
Usefulness of the CeCl3 in the Preparation of Nitrogen-Containing Substituted Heterocycles
No full textHeterocyclic compounds are of considerable interest because of their extensive use in the design of biologically active molecules and advance organic materials, and, in general, cyclization of acylic precursors is the method used for their preparation
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