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CeCl3·7H2O/NaI as Lewis acid catalyst in the Povarov reaction for the synthesis of functionalized tetrahydroquinolines
No full textMany different biologically active compounds contain the widespread scaffold of tetrahydroquinolines. Hence the interest toward their synthesis has stimulated the development of several synthetic strategies, among which the Povarov reaction is one of the most applied. The performance of this three-components imino Diels-Alder reaction can be improved by Lewis acid catalysis. In the last years the search for more economic and environmentally benign synthetic methodologies has stimulated the use of nontoxic and nonexpensive catalytic systems, and in this perspective Cerium trichloride has became interesting because of its low toxicity and cost and for the ease of application also in non anhydrous conditions.2,3
Here we describe the study of the CeCl3·7H2O/NaI system as Lewis acid catalyst in the Povarov reaction for the synthesis of substituted tetrahydroquinolines.
The reaction proceeds well, in acceptable reaction times and up to 86% yield. Both syn and anti diastereomers of the final tetrahydroquinoline can be obtained preferentially, depending on the reaction conditions, because the stereoselectivity is opposite in acetonitrile or in solventless conditions. Also substituted anilines and aromatic aldehydes have been employed with good results. A further investigation was made about the mechanism, to understand the formation of the main byproducts
CeCl3 catalyzed imino Diels-Alder reactions: hydrated vs anhydrous
Full text linkAza-Diels-Alder reaction is a straightforward way to synthesize useful nitrogen containing heterocyclic structures.1 In particular, the known reaction between imines and Danishefsky’s diene has proved to be an excellent way to obtain the 1,2-substituted-2,3-dihydropyridinone scaffold, widely present in bioactive small molecules and versatile building block for the synthesis of more complex structures.2
The reaction of Danishefsky’s diene with aromatic imines has been widely studied in last years, anyway less examples of the same reaction involving imines derived from aliphatic amines or aldehydes are present. For this reason the possibility to extend the potentiality of this reaction performing it on a large variety of imines was studied, under the Lewis acid promoting system CeCl3.7H2O/CuI, previously applied with success3 in many other synthetic methodologies.
Imines 3 were prepared by direct condensation of aliphatic or aromatic amines and aldehydes and then the diene was added together with the catalyst, obtaining dihydropyridinones 4 with good to excellent yields in short reaction times. To extend the scope of this work, also imines derived from aminoacids were tested as dienophiles.
The only moderate diastereoselectivity and the long time needed with some homochiral dienophiles prompted us to have a deeper insight into the mechanism, with the conclusion that the reaction proceed also through a slower competitive Mannich-Michael pathway, favoured by the presence of water in the catalyst.
1) Buonora, P.; Olsen, J.-C.; Oh, T. Tetrahedron 2001, 57, 6099-6138.
2) Cant, A. A.; Sutherland, A. Synthesis 2012, 44, 1935-1950.
3) Bartoli, G.; Marcantoni, E.; Marcolini, M.; Sambri, L. Chem. Rev. 2010, 110, 6104-6143
An Efficient Lewis Acid Catalyzed Povarov Reaction for the One-Pot Stereocontrolled Synthesis of Polyfunctionalized Tetrahydroquinolines
Full text linkAn easy and efficient synthetic methodology for the one-pot stereocontrolled synthesis of tetrahydroquinolines through Lewis acid activated Povarov reaction is described. The protocol takes advantage of the very cheap, easy to handle, and environmentally friendly cerium trichloride as catalyst and allows to obtain either the anti- or the syn-isomer of the final tetrahydroquinoline with good selectivity, by performing the reaction in solvent or solventless conditions. The scope of the reaction is expanded to the one-pot synthesis of N-alkyltetrahydroquinolines through a very efficient iminium-Povarov approach. A deeper insight on the reaction system was provided by the study on the side reactions occurring in the reaction conditions and on the nature of the stereoselectivity
Complessi di rame(I) con leganti tris(azolil)borati e fosfine monodentate: sintesi e studi biologici
No full textI complessi di Cu(I) rappresentano un’emergente alternativa agli antitumorali a base di platino. Alla base del recente interesse scientifico vi è sia l’alterazione del metabolismo del rame nelle cellule tumorali, sia la diversa risposta tra cellule normali e cellule tumorali. Nell’ottica di sintetizzare stabili complessi di Cu(I) combinando le proprietà dei leganti scorpionati con la capacità riducente di fosfine terziarie, sono stati recentemente sintetizzati e caratterizzati complessi tetraedrici di Cu(I) del tipo TpCuP, dove Tp è un N,N,N-tris(azolil)borato e P è una fosfina terziaria (Figura 1).2 Tutti i complessi sono stati valutati per la loro attività antiproliferativa nei confronti di linee cellulari tumorali umane, anche cisplatino resistenti e i due complessi più efficaci, [HB(pz)3]Cu(PCN) e [HB(pz)3]Cu(PTA), hanno evidenziato: a) selettività verso il tessuto tumorale rispetto alle cellule sane, b) inibizione dell’attività del proteosoma 26S associata allo stress del reticolo endoplasmatico, c) attivazione dell’UPR. Studi morfologici hanno inoltre rivelato un’ampia vacuolizzazione citoplasmatica coerente con un meccanismo di morte cellulare parapoptotica. Infine, l'efficacia antitumorale di [HB(pz)3]Cu(PCN) è stata validata nel modello murino del carcinoma polmonare di Lewis
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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