1,720,962 research outputs found
Synyhesis of a renewable hydroperoxide from (+)-norcamphor:implications of steric modification of the bicyclic framework on asymmetric sulfoxidation
No full textA renewable tertiary hydroperoxide has been efficiently synthesized in 83% overall yield starting from commercially available (+)-endo-2-norborneol. This oxygen donor, derived from (+)-norcamphor, when employed in Ti(O i-Pr)(4)-catalyzed sulfoxidations, proved to be considerably more reactive when compared to a previously reported camphor-derived hydroperoxide. Reduced steric hindrance of the new oxidant lowered the level of asymmetric induction achieved in the oxidation, but stereo-convergent kinetic resolution has been exploited to improve enantioselectivity. Excellent recovery (95%) of the tertiary alcohol at the end of the sulfoxidation provides a highly advantageous chiral resource saving protocol
Catalytic asymmetric epoxidation of allylic alcohols using a renewable hydroperoxide
No full textSharpless modified asymmetric epoxidation of allylic alcohols can be successfully performed using an easily accessible and renewable tertiary furyl hydroperoxide in the presence 20 mol% of the chiral Ti(O-i-Pr)(4)/L-DIPT/MS 4 Angstrom system
Synthesis of easily accessible enantiopure tertiary furyl hydroperoxide and use in asymmetric sulfoxidation
No full textEnantioselective epoxidation of chalcones and naphtoquinones by (+)norcamphor-derived hydroperoxide
No full text(+)-Norcamphor-derived hydroperoxide has been employed in the asymmetric epoxidation of electron poor alkenes such as trans-chalcones and naphthoquinones. Optimization of the reaction conditions required the employment of n-BuLi/THF at -20degreesC to achieve ees up to 58%. The epoxide of vitamin K-3 has now been obtained with the best up to now reported value of enantioselectivity (51% ee)
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
Convenient procedure of Horner-Wadsworth-Emmons olefination for the synthesis of simple and functionalised a,b-unsaturated nitriles
No full textA mild and practical procedure of Horner-Wadsworth-Emmons olefination promoted by lithium hydroxide and alpha-cyano phosphonates has been set up for the synthesis of alpha,beta-unsaturated nitrites. The reaction conditions are tolerated by functionalized ketones and the exclusive formation of E-gamma-hydroxy alpha,beta-unsaturated nitrites has been observed
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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