1,720,960 research outputs found
Synthesis of new enantiopure trans-3,4-diaminocaranes from (+)-3-carene.
No full textA synthetic strategy to obtain new enantiopure trans-3,4-diaminocaranes derived from (+)-3-carene via a stereoselective methodology is described. The stereoselective preparation of 3,4-a-carene- or 3,4-b-carene-epoxide is followed by a ring opening by sodium azide to obtain the azido-alcohols. Subsequent cyclization affords the corresponding aziridine diastereoisomers, which are converted to azido amines by opening of the aziridine rings by sodium azide and then reduced to the final diamine diastereoisomers. The absolute configurations of the final diamines and of novel intermediates are established by 1H-NMR spectra correlated with conformational analysis supported by molecular modeling
Enantiopure a-Imino Glyoxylate: Versatile Substrate for the Spontaneous Asymmetric Synthesis of Unnatural Hydroxyaryl Glycinates.
No full textA novel synthesis of useful enantiomerically pure arylglycinates via spontaneous reaction between phe-nol or naphthol derivatives and enantiopurea-imino glyoxylate in the absence of an acid catalyst is reported. A library of enantiopure substituted phenol or naphthol glycinates was obtained in good yields and high diastereoselectivities. Diastereoisomerically pure aryl glycinates were obtained by direct flash chromatography separation of the crude reaction mixture. The free OH moiety of the phenols or naph-thols contributed to the activation of the imino group to form an intermolecular hydrogen bond and pro-moted the reaction in the absence of an acid catalyst, as shown in the transition state reported. The diastereoselectivity is due to thermodynamic control in the addition step
Betti Reaction of Cyclic Imines with Naphthols and Phenols - Preparation of New Derivatives of Betti's Bases
No full textA large library of aminocycloalkylphenols and -naphthols is obtained by the Betti reaction between activated phenols and naphthols and five- and six-membered cyclic imines. Due to the formation of an intramolecular hydrogen bond in the transition state, the attack takes place regioselectively at the position adjacent to the hydroxy group of the aromatic compounds. X-ray crystallography and chirooptical methods (electronic circular dichroism) were used to ascertain the ab-solute configuration of two aminoalkylnaphthols obtained, after resolution of the corresponding racemates with (R,R)-tartaric acid. In addition, some aminoalkylnaphthols and -phenols were alkylated at the nitrogen atom to obtain N-methylated products in good yields
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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