1,721,000 research outputs found
Last decade of unconventional methodologies for the synthesis of substituted benzofurans
No full textThis review describes the progress of the last decade on the synthesis of substituted benzofurans, which are useful scaffolds for the synthesis of numerous natural products and pharmaceuticals. In particular, new intramolecular and intermolecular C–C and/or C–O bond-forming processes, with transition-metal catalysis or metal-free are summarized. (1) Introduction. (2) Ring generation via intramolecular cyclization. (2.1) C7a–O bond formation: (route a). (2.2) O–C2 bond formation: (route b). (2.3) C2–C3 bond formation: (route c). (2.4) C3–C3a bond formation: (route d). (3) Ring generation via intermolecular cyclization. (3.1) C7a-O and C3–C3a bond formation (route a + d). (3.2) O–C2 and C2–C3 bond formation: (route b + c). (3.3) O–C2 and C3–C3a bond formation: (route b + d). (4) Benzannulation. (5) Conclusion
Recent Advances in Synthetic Strategies to 2,3-Dihydrobenzofurans
Full text linkThis review gives an overview on recent developments in methods for the construction of compounds with the 2,3-dihydrobenzo furan core in the period 2012 to 2019. Interest in 2,3-dihydrobenzofurans is constantly increasing. The methods are divided into intermolecular and intramolecular approaches. Intermolecular approaches are subdivided according to the parent intermediate for the key reaction, while intermolecular approaches are subdivided according by which bond is formed in the key reaction. The transformation of benzofurans to dihydrobenzofurans and other miscellaneous methods are also discussed. Approaches useful for the synthesis of natural products are emphasized. 1 Introduction 2 Intermolecular Approaches 2.1 o -Quinone Methides and o -Quinones 2.2 p -Quinone Methides and p -Quinones 2.3 Nitrogen-Containing Phenols and Quinones 2.4 o -Hydroxyphenylcarbonyl Derivatives and Phenols 2.5 Miscellaneous 3 Intramolecular Approaches 3.1 O-C2 Bond Forming 3.2 C2-C3 Bond Forming 3.3 C3-Aryl Bond Forming 3.4 O-Aryl Bond Forming 4 From BF to DHB 5 Rearrangements and Aromatizations
Structural Insights into the TES/TFA Reduction of Differently Substituted Benzofurans: Dihydrobenzofurans or Bibenzyls?
No full textVarious polysubstituted benzofurans were reduced by using triethylsilane in trifluoracetic acid. 2,3-Dihydrobenzofurans or bibenzyl compounds were obtained in high yields, depending on the nature of the substituents at C2 and on the benzene ring of the core structure. A p -anisole substituent at C2 of benzofurans always led to the corresponding bibenzyls
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
Regio- and Diastereo-Selective Biomimetic Synthesis of (±)-ε-Viniferin by NIS and Resveratrol
No full textIn this work, we describe the synthesis of (±)-permethylated-ε-viniferin from resveratrol by successive iodination, methylation and dehalogenation reactions. Iodination reaction by N-iodosuccinimide (NIS) was studied to optimize and confirm a proposed radical mechanism. Switching to acetyl protecting group, a new straightforward regio- and diastereo-selective biomimetic synthesis of (±)-ε-viniferin was obtained. Permethylated and free ε-viniferin were isolated up to 20 %yield
Regio- and Diastereoselective Organo-Zinc-Promoted Arylation of trans-2,3-Diaryloxiranes by Arylboronic Acids: Stereoselective Access to trans-2,3-Diphenyl-2,3-dihydrobenzofuran
No full textortho-Oxo substituted trans 2,3-diaryloxiranes were regio- and stereoselectively arylated by arylzinc reagents, obtained from the corresponding boronic acids by B–Zn exchange. The reaction was quite general, irrespective to the aryl nucleophile and proceeded via a ring opening at the α-carbon with respect to the substituted aryl ring. The stereoselectivity was from high to complete toward the alcohol resulted from retention of configuration at the electrophilic carbon. The method allowed a direct and high yielding access to trans 2,3-diphenyl-2,3-dihydrobenzofuran, which is a key structural motif in resveratrol dimers as viniferins. The use of enantioenriched starting diaryloxiranes resulted in no loss of stereochemical integrity in the final trans 2,3-dihydrobenzofuran, which was characterized for the first time in enantioenriched form
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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