1,720,962 research outputs found
Synthetic Applications of 2-(Azidomethyl)allyltrimethylsilane
No full textStarting from commercially available 2-(chloromethyl)-allyltrimethylsilane, the corresponding 2-(azidomethyl)allyl silane was prepared through reaction with NaN3. The product was stable upon isolation and storage and could be used for thermal cycloaddition of the azido group with alkenes to give allylsilane-containing triazolines or aziridines. This reaction was not accelerated by microwave (MW) dielectric heating, however, the azide fragment undergoes MW-assisted Cu(I)-catalyzed cycloaddition with a range of alkynes (including ynamides). Lewis acid mediated Hosomi-Sakurai reaction of the allylsilane with aldehydes was also possible. A one-pot transformation into different triazolo-containing homoallyl alcohols was carried out through a sequence of Cu(I)-catalyzed azide cycloaddition under MW dielectric heating and BCl3-mediated reaction with aromatic aldehydes. © Georg Thieme Verlag Stuttgart · New York
Microwave Assisted Hydrogenation of Pyridinecarboxylates: a Convenient Access to Valuable Scaffolds for Diversity Oriented Synthesis
No full textHydrogenation of pyridine under Microwave (MW) dielectric heating is a valuable method for a rapid approach to piperidine synthesis. Starting from easily available pyridinecarboxylate derivatives, aminopipecolic scaffolds were prepared and further decorated with a procedure potentially useful for parallel synthesis. MW hydrogenation on PtO2 proceeded with high stereoselectivity and low catalyst loading under mild conditions (80°C and 850 MPa of H2 pressure). MWs were also effective to perform a Pinner reaction on 2-cyano-nitropyridines to obtain the corresponding methyl nitropyridine carboxylates. A general procedure to decorate the 3-, 4-, and 5-amino-pipecolic derivatives obtained from the pyridine hydrogenation has been also developed
[4+2]Cycloaddition on densely functionalized cyclopentadiene
No full textThe Diels-Alder (DA) and hetero-Diels-Alder (HDA) reaction of N-(2,4-dicyano-1,5-dimethyl-3-phenylcyclopenta-2,4-dienyl)-2,2,2-trifluoroacetamide 1 can be conveniently used for the synthesis of biarylic and polycyclic compounds, depending on whether you use alkynes or alkenes as dienophiles. We observe a totally regioselectivity and endo-diastereoselectivity of the cycloaddition reactions
Synthesis of Isoxazolopyridobicyclooxacalix[4]arenes: A New Family of Heteracalixarene Systems
No full textA new family of isoxazolopyridobicyclooxacalix[4]arenes was obtained by reaction of dichloroisoxazolopyridines with phloroglucinol. X-ray crystallography and density functional calculations were used for their structural determination and evaluation of their chemical properties. Their role as metal chelators was studied by mass spectrometry. This new family of heteracalixarenes is of potential interest for host-guest interactions
Aryl triazole compounds with antitumoural activity
No full texte present invention relates to aryl triazole derivs. of Formula I having antitumoral activity through, as one possible biol. target, the mol. chaperone heat shock protein 90 (Hsp90) inhibition. The invention includes the use of such compds. in medicine, in relation to cancer disease as well as other diseases where an inhibition of Hsp90 is responsive, and the pharmaceutical compn. contg. such compd
Stereoselective synthesis of trans-beta-lactams by palladium-catalysed carbonylation of vinyl aziridines
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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
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