1,721,003 research outputs found
An efficient diastereoselective route to differentially protected anti-4-amino-1-alken-3-ols
No full textMultidecagram Scale Synthesis of an Endoperoxide, Precursor of Anti-malarial and Anti-leishmanial Agents, via Free-Radical [2 + 2 + 2] Annulation with Molecular Oxygen
Full text linkFrom screening experimental parameters to scaling up, a safe approach is reported for the multidecagram scale preparation of methyl ester of 6,6-dibutyl-3-hydroxy-3-methyl-1,2-dioxane-4-carboxylic acid (7), a flexible common intermediate for the synthesis of a variety of anti-malarial and/or anti-leishmanial compounds. The critical feature of the reaction is the use of a pure oxygen flow under batch conditions using methyl acetoacetate and 2-butyl-1-hexene as reagents, and a mixture of Mn(II) and Mn(III) acetates as catalysts, in acetic acid. Once the best solvent, catalyst loading, temperature, and reaction time in the small-scale procedure (10 mL vial) were defined, the process was adapted up to a 3 L flask, eventually resulting in the production of about 70 g of 7. The developed reaction protocol gives a satisfactory result considering: (i) the inexpensive starting materials used, (ii) the 100% atom economy of the [2 + 2 + 2]-annulation reaction, (iii) the stoichiometric ratio of the two reagents (only oxygen is used in excess) coupled with low catalyst loading, and (iv) the mild conditions adopted. The calorimetric studies allow us to classify this reaction as an inherently safe process. On a larger scale, the possible formation of a flammable vapor mixture in the reactor headspace was minimized using two parallel continuous flows of oxygen and argon, thus ensuring a constant headspace vapor phase renewal
A Short Route to 2-(6-Methoxycarbonylhexyl)-cyclopent-2-en-1-one
No full textThe prostaglandin intermediate 2-(6-methoxycarbonylhexyl)-cyclopent-2-en-1-one (5) has been prepared by a short synthetic sequence, consisting of the reaction of 2-(1,3-dioxolan-2-yl)-ethylmagnesium bromide (1) with methyl 9-chloro-9-oxononanoate (2), followed by cleavage of the dioxolane ring of 3 and base-induced cyclisation of 4
Active Metals from Potassium-Graphite. Palladium-Graphite as Catalyst in the Hydrogenation of Nitro-compounds, Alkenes, and Alkynes
No full textPalladium-graphite, prepared by reduction of PdCl2 by means of C8K in 1,2-dimethoxyethane, is an effective catalyst for the hydrogenation of aromatic nitro-compounds, alkenes, and alkynes to anilines, alkanes, and (Z)-alkenes, respectively
A new protocol for the acetoxyallylation of aldehydes mediated by indium in THF
No full textA new precursor of a formal 1-hydroxy allyl anion is represented by 3-bromo-1-acetoxy-1-propene, which is synthesized by the ZnCl2-catalyzed
addition of acetyl bromide to propenal. 3-Bromo-1-acetoxy-1-propene reacts with indium powder in THF to give the corresponding 3-acetoxylated
ally indium complex, which regioselectively adds to aldehydes, affording monoprotected 1-en-3,4-diols. Diastereoselectivity mainly depends
on the nature of the aldehyde; saturated aldehydes afford anti adducts, whereas the r,â-unsaturated aldehydes preferentially lead to the syn
isomer
Active Metals from Potassium-Graphite. Palladium-Graphite-catalysed Vinylic Substitution Reactions
No full textPalladium-graphite, prepared by reduction of PdCl2 by means of C8K, is a convenient catalyst for the arylation or alkenylation of activated carbon-carbon double bonds with aryl or vinyl iodides
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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