1,720,974 research outputs found
New environmental friendly N-aryl indolines synthesis through C-N bond formation
No full textThe indoline skeleton is an ubiquitous scaffold found in a range of biologically active alkaloid and pharmaceutically active compounds. Indolines have also been successfully employed as chiral auxiliaries in asymmetric synthesis.1-2 On the other hand indolines are also useful for various application ranging from dyes, dye sensitized solar cell, to fuel cell (H2 storage).3 Our research group is always interested in heterocyclic systems synthesis and to this goal Pd-catalyzed reactions have been extensively studied.4
Among the known Pd-catalyzed reactions typologies Heck reaction, Buchwald-Hartwig reaction, oxidative coupling, arylation have been reported previously by our research group. In particular the amination reaction are nowadays one of the most powerful tool to obtain C-N bond formation.5-8 The evolution of this reaction was toward the use of weak bases in order to leave intact other functional groups. The further evolution was addressed to improve yield and applicability, and this goal was achieved using different ligands and through their optimization. Today we try to further enlarge the applicability and to use environmental friendly procedures. Last but not least we try to develop economic and scalable synthesis to switch the use of this reactions from research to industry. We present here a new kind of solvent “QUASI-free” reaction, combined with the use of a commercially available ligand and the use of a weak and cheap base, K2CO3. Irradiation by microwaves is the other key feature of this protocol
Palladium-catalyzed intramolecular arylation of electron-poor heterocycles
No full textFormation of aryl-aryl bonds is a very interesting reaction especially for the synthesis of new chemical entities in drug discovery[1]. One of the most utilized method is the metal-catalyzed cross-coupling reaction with the limitation of the use of activating group in both of the arene coupling partner. Recently palladium-catalyzed direct arylations have emerged as attracting alternative. The advantage of this reaction consist in the opportunity to start from very simple building blocks: a non-activated aryl C-H bond and an aryl-halide. Most literature citation involves electron rich substrate[2], on the contrary there are only few examples regarding electron-poor heterocycles[3]; we report intramolecular version of this reaction regarding azines and diazines. Starting from functionalized nicotinic amides and 1,2-, 1,3- and 1,4-diazine amides, in only one step, azapolycyclic systems are obtaine
SYNTHESIS AND REACTIVITY OF N-CONTAINING HETEROCYCLES THROUGH CATALYTIC SYSTEMS.
Full text linkN-containing heterocycles are the more represented in natural products and drugs. Our research has been focused on various aspects of heterocycles synthesis and reactivity. For this purpose we use transition metals catalysis, among which Pd has a central role due to the existence of different and easily and interconvertible oxidation states, Pd(0), Pd(II) and Pd(IV).
For the arylation reaction electron poor aryl derivatives are problematic substrates, but we are successful in apply an intramolecular Pd(0) catalyzed reaction, in ligand free conditions, to synthesize azine and diazine polyheterocycles.
Following our study on the reactivity and functionalization of indole derivatives we focus our attention on the amination reaction applied to the heterocycle indoline. The indoline skeleton is a ubiquitous scaffold found in many biologically active alkaloids and pharmaceutically active compounds, useful even as chiral auxiliary and for advanced materials. We selected the best conditions to functionalize this heterocycle at the nitrogen atom; then we find environmental friendly conditions using a solvent-free, microwaves assisted, reaction method and substantially reducing the catalyst load. Further to this we demonstrate the possibility of making Pd(0)-catalyzed amination reactions even in ligand-free conditions.
In the third part we study a new synthesis of tetracyclic 1,4-Benzodiazepin-5-ones. The exploited reactions are Pd(0) catalyzed heterocyclization on imidazolidinones allenylamide followed by 1,3-dipolar cycloaddition. In the last step of the synthesis we obtain an unexpected total diasteroselectivity so we make a DFT and HF computational study that justify our results also thanks to the use of the recent QTAIM theory.
In the last part we use Pd(II) and Au(III)-catalyzed reactions to realize C-H activation reaction. Starting from isoxazol-5-ones we obtain a solvent based regioselectivity in the alkenylation with acrylates or propiolates. The use of Pd(II)/O2 catalysis with acrylates lead to regioselectivity but with low yield; Au(III) catalysis with propiolates gives better yield and shows a complete regioselectivity
Efficient palladium-catalyzed direct arylation of azines and diazines using ligand- free conditions
No full textThe use of the palladium-catalyzed direct arylation was successfully tested on different electron-deficient heterocycles. The results demonstrate the effectiveness of the method based on the intramolecular coupling reaction providing polyazacyclic systems. This new application was obtained by using ligand-free conditions with the mixture of Pd(OAc)2 and TBAC as catalytic system. With suitable substrates different products arising from regioselective coupling were observed
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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