1,720,978 research outputs found
Rh(III)-catalyzed 7-azaindole synthesis via C-H activation/annulative coupling of aminopyridines with alkynes
No full textAn efficient Rh(III)-catalyzed 7-azaindole synthesis was developed via C-H activation/annulative coupling of aminopyridines with alkynes. The reaction was highly regioselective and tolerated various functional groups, permitting the construction of various 7-azaindoles. © The Royal Society of Chemistry 20151171sciescopu
Synthesis of heterocyclic-fused benzopyrans via the Pd(II)-catalyzed C–H alkenylation/C–O cyclization of flavones and coumarins
No full textAn efficient and practical method for effecting a tandem C-H alkenylation/C-O cyclization has been achieved via the C-H functionalization of flavone derivatives. The synthetic utility of the one-pot sequence was demonstrated by obtaining convenient access to coumarin-annelated benzopyrans. The reaction scope for the transformation was found to be fairly broad, affording good yields of a wide range of flavone-or coumarin-fused benzopyran motifs, which are privileged structures in many biologically active compounds.131311sciescopu
Synthesis of heterocyclic-fused benzofurans via C–H functionalization of flavones and coumarins
No full textAn efficient method to effect C–O cyclization was developed via the C–H functionalization of chromones and coumarins, affording heterocyclic-fused benzofurans.242811sciescopu
A copper-mediated cross-coupling approach for the synthesis of 3-heteroaryl quinolone and related analogues
No full textAn efficient and practical method for the direct cross-coupling between quinolones and a range of azoles was developed via copper-mediated C-H functionalization. This synthetic strategy provides a convenient access to a variety of C3-heteroaryl quinolones, quinolinone, nalidixic acid, uracil, pyridone and chromone derivatives, which are prominent structural motifs in many biologically active compounds.1991sciescopu
Visible-light-induced cascade radical ring-closure and pyridylation for the synthesis of tetrahydrofurans
No full text© 2019 The Royal Society of Chemistry. Reported is a novel visible-light-enabled alkoxy radical ring-closure and pyridylation from N-alkenyloxypyridinium salts serving as both alkoxy radical precursors and heteroaryl sources. This strategy features a photoredox tandem radical process involving a sequential fragmentation of an N-alkoxypyridinium salt, a radical cyclization process, and a pyridylation process. This method exhibited broad substrate scope, good functional group compatibility, and metal-free mild conditions, offering a powerful synthetic tool for assembling various pyridine-tethered tetrahydrofurans and late-stage functionalization of complex biorelevant molecules. Moreover, radical cascade cyclization could be successfully achieved, leading to the synthesis of previously challenging and important pyridine-tethered bicyclic oxaspiro ring systems11sci
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
Stereoselective construction of sterically hindered oxaspirocycles: Via chiral bidentate directing group-mediated C(sp3)-O bond formation
No full textThe systematic investigation of chiral bidentate auxiliaries has resulted in the discovery of a chiral 2,2-dimethyl-1-(pyridin-2-yl)propan-1-amine-derived directing group that enables stereoselective palladium(ii)-catalyzed intramolecular C(sp3)-O bond formation. This new chiral directing group exhibited high reactivity in the activation of methylene C(sp3)-H bonds with excellent levels of stereoselectivity (a diastereomeric ratio of up to 39:::1), which allowed the construction of a wide range of oxaspirocycles. Mechanistic investigations were also conducted to elucidate the reaction mechanism and understand the origin of the diastereoselectivity. DFT calculations suggest that only modest levels of diastereoselectivity are accomplished at the rate-determining C-H metalation-deprotonation step and the d.r. is further enriched at the reductive elimination step. © 2018 The Royal Society of Chemistry11sciescopu
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