1,720,960 research outputs found
FRAGMENTATION-CYCLIZATION REACTIONS BY PHOTOINDUCED ELECTRON-TRANSFER
No full textKIRSCHBERG T, Mattay J. FRAGMENTATION-CYCLIZATION REACTIONS BY PHOTOINDUCED ELECTRON-TRANSFER. Tetrahedron Letters. 1994;35(39):7217-7220.Irradiation of unsaturated bicyclo[4.1.0]heptanones and bicyclo[3.1.0]hexanones under reductive PET conditions leads to a regioselective cleavage of the cyclopropane moiety followed by cyclization. By this method various types of ring anellated and spirocyclic compounds are accessible
Reductive cyclization of alpha-cyclopropylketones with alkynyl- and aryl-tethered substituents
No full textFagnoni M, Schmoldt P, Kirschberg T, Mattay J. Reductive cyclization of alpha-cyclopropylketones with alkynyl- and aryl-tethered substituents. Tetrahedron. 1998;54(23):6427-6444.Photoinduced electron transfer (PET) reactions of alpha-cyclopropyl-substituted ketones and triethylamine (TEA) were used to initiate the cyclopropylcarbinyl-homoallyl rearrangement. The intramolecular cyclization reaction onto triple bonds was performed yielding bicyclic and spirocyclic compounds. Furthermore, in some preliminary studies it was shown that even intramolecular aromatic substitutions are feasible. (C) 1998 Elsevier Science Ltd. All rights reserved
Photochemical reactions of cyclopropyl ketones by electron transfer
No full textSchmoldt P, Kirschberg T, Fagnoni M, Mattay J. Photochemical reactions of cyclopropyl ketones by electron transfer. JOURNAL OF INFORMATION RECORDING. 1998;24(3-4):249-252.Photoinduced electron transfer (PET) from triethylamine (TEA) to cyclopropyl ketones initiated a cyclopropylcarbinyl-homoallyl rearrangement. Attack of the so formed homoallyl radicals on a terminally unsaturated side chain gave various bicyclic products the structure of which depends on the position and length of that side chain
Photoinduced electron transfer reactions of alpha-cyclopropyl- and alpha-epoxy ketones. Tandem fragmentation-cyclization to bi-, tri-, and spirocyclic ketones
No full textKirschberg T, Mattay J. Photoinduced electron transfer reactions of alpha-cyclopropyl- and alpha-epoxy ketones. Tandem fragmentation-cyclization to bi-, tri-, and spirocyclic ketones. The Journal of Organic Chemistry. 1996;61(25):8885-8896.Reductive photoinduced electron transfer (PET) reactions have been performed with various bicyclic alpha-cyclopropyl-substituted ketones and tertiary amines. The reaction resulted in a regioselective cleavage of one cyclopropyl bond under formation of an exocyclic radical with an endocyclic enolate unit. In the case of bicyclic ketones with an unsaturated side chain, various bicyclic, spirocyclic, and tricyclic products are accessible via radical cyclization, depending on the position of the alkenyl substituent. In addition to triethylamine, N-silylated amines have also been used as electron donors, leading to a variety of compounds, among them are silylated fragmentation products, indicating that a proton is transferred from not only the amine radical cation but also the cationic silyl group. The intramolecular Paterno-Buchi reaction has also been studied for cyclopropane derivatives of the jasmone type leading to tetracyclic oxetanes. Finally, alpha-epoxy-substituted ketones have been investigated under PET conditions, yielding ring-opened products
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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