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Asymmetric synthesis of cyclopentenones with benzylic alpha-quaternary carbon stereogenic centres from furans
No full textA new procedure for the synthesis of cyclopentenones containing benzylic alpha-quaternary carbon stereogenic centres is reported. This method makes use of a one-pot alkylation-elimination sequence from readily available starting materials and simple procedures, which makes it useful for the large-scale preparation of densely functionalised cyclopentanoids. (C) 2004 Elsevier Ltd. All rights reserved
Enantioselective synthesis of gamma,delta-disubstituted beta-hydroxy delta-lactones from furans: Synthesis of (+)-prelactone B and its C-4 epimer
No full textA new method for the enantioselective synthesis of gamma,delta-disubstituted beta-hydroxy delta-lactones (5,6-dialkyl-5,6-dihydropyran-2-ones) is reported and exemplified for (+)-prelactone B and its C-4 epimer. Our approach is based on the ring-enlargement of suitably functionalized optically pure 4-hydroxycyclopentanones, which are readily obtained from chiral 4-hydroxycyclopent-2-enones derived from furans. The procedure is amenable to the large-scale synthesis of the title compounds
Regio- and stereoselective addition of Grignard and organolithium reagents to 4-hydroxy-2-cyclopentenones
No full texta highly regio- and stereoselective
method for the 1,2- or 1,4-addition reactions to 4-hydroxy-
2-cyclopentenones has been devised, which makes use of
readily available organolithium and Grignard reagents.
This procedure allows for stereochemistry complementary
to that observed in the 1,4-addition of organocuprates
and makes possible the attachment of aromatic
groups to carbons C-2 and C-3 of cyclopentenones 5 or 6 and carbons C-4 and C-5 of cyclopentanones 7, which are
of interest for further elaboration into biologically active
target
Asymmetric C-C bond formation by the mixed oxidative coupling of 1,1 '-bi-2-naphthyl esters
No full textAsymmetric C-C bond formation was effected by the oxidative coupling of two different ester enolates using (R)-(+)-1,1'-bi(2-naphthol) as a common tether which served to link together both ester moieties in an asymmetric environment. Reduction of the corresponding succinates afforded diastereomerically pure 2,3-disubstituted-1,4-butanediols
Regioselective synthesis of trisubstituted cyclopentadienyl ligands from furans
No full text1,2,3- And 1,2,4-trisubstituted cyclopentadienyl manganese tricarbonyl compounds have been synthesized regioselectively from furans following a common synthetic strategy. The key steps include the transformation of furylcarbinols into hydroxycyclopentenones followed by the conjugate addition of Grignard reagents under chelation directed conditions. This affords hydroxycyclopentanones which can be dehydrated to cyclopentenones. These compounds are further elaborated into the final targets by the 1,2-addition of organolithium reagent
Stereoselectivity control in the Rh(I)-catalyzed conjugate additions of aryl and alkenylboronic acids to unprotected hydroxycyclopentenones
No full textThe stereoselective Rh(I)-catalyzed conjugate addition reaction of aryl and alkenylboronic acids to unprotected 2-phenyl-4-hydroxycyclopentenone is presented. The free OH group on the substrate is responsible for the stereochemistry, which is cis for arylboronic derivatives. In the case of the alkenylboronic compounds, the stereochemistry can be tuned to either a cis (bases as additives) or trans addition (CsF as additive) without the need of protecting groups
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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