1,720,980 research outputs found
Novel Photocatalytic Approaches for Ecosustainable Synthesis
Full text linkOver the past decades, photochemical synthesis, i.e. organic synthesis that uses light as
source of energy to break and forge bonds, has vehemently re-emerged as an important theme of research in
ecosustainable organic chemistry. Thanks to the possibility to excite a precise functional group in a complex reaction
mixture and the peculiar reactivity of the so-formed excited states, photochemistry is very attractive for both synthetic
researchers and industrial practitioners. An added value to this activation manifold is represented by photocatalysis: in
these reactions, the substrate does not absorb light directly, instead low-energy light is absorbed by a purposely added
molecule (photocatalyst, PC) that converts this energy into chemical energy for substrate activation, thus limiting
undesired processes. This activation step can occur via Single-Electron Transfer (SET), Hydrogen-Atom Transfer
(HAT) or Energy Transfer (ET) and in the present thesis I decided to study their application to develop novel
ecosustainable synthetic protocols
Merging photoinduced protic HAT and radical-polar crossover for olefin difunctionalization
No full textIn this issue of Chem Catalysis, Wei, Shi, and co-workers describe a robust methodology for the regioselective difunctionalization of alkenes by combining photocatalyzed hydrogen atom transfer for the generation of electrophilic radicals and radical-polar crossover. The simplicity of the methodology suggests its rapid uptake for syn-thetic purposes
Hydrogen Atom Transfer (HAT): A Versatile Strategy for Substrate Activation in Photocatalyzed Organic Synthesis
No full textThe adoption of hydrogen atom transfer (HAT) in a photocatalytic approach, in which an excited catalyst is responsible for substrate activation, offers unique opportunities in organic synthesis, enabling the straightforward activation of R–H (R = C, Si, S) bonds in desired reagents. Either a direct strategy, based on the intrinsic reactivity of a limited number of photocatalysts in the excited state, or an indirect one, in which a photocatalytic cycle is used for the generation of a thermal hydrogen abstractor, can be exploited. This microreview summarizes the most recent advances (mainly from the last two years) in this rapidly developing area of research, collecting the selected examples according to the nature of the species promoting the HAT process. From the synthetic point of view, this area has led to the development of a plethora of strategies for C–C, C–Si, C–N, C–S, and C–halogen (particularly, fluorine) bond formation, as well as for oxidation reactions
Vinylpyridines as Building Blocks for the Photocatalyzed Synthesis of Alkylpyridines
No full textThis is the final peer-reviewed manuscript accepted for publication in Chemistry - A European Journal
Citation of the published version is: Chem. Eur. J. 2017, 23, 6527-653
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
Visible Light-Induced Halogen-Atom Transfer by N-Heterocyclic Carbene-Ligated Boryl Radicals for Diastereoselective C(sp3)–C(sp2) Bond Formation
Full text linkPhotoinduced Halogen-Atom Transfer (XAT) has rapidly emerged as a programmable approach to generate carbon-centered radical intermediates, mainly relying on silyl and α-aminoalkyl radicals as halogen abstractors. More recently, ligated boryl radicals have also been proposed as effective halogen abstractors under visible-light irradiation. In this study, we describe the use of this approach to enable C(sp3)–C(sp2) bond formation via radical addition of carbon-centered radicals generated via XAT onto chloroalkynes. Our mechanistic investigation reveals a complex interplay of highly reactive radical intermediates which, under optimized conditions, delivered the targeted vinyl chlorides in excellent yields and Z:E ratios. Finally, we demonstrated the synthetic value of these products in transition metal-based cross-coupling reactions
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
Mechanochemical Aerobic Activation of Metallic Copper for the Synthesis of 1,4‐Allenynes
No full textMechanical activation of zero-valent metals is emerging as a new paradigm in sustainable synthesis, opening up a broad swath of chemical space under more practical conditions than solution-phase methods. Contrary to its neighboring elements in the periodic table, copper has been significantly overlooked in this domain, especially for C.C bond formation. Herein, a mechanochemical method for synthesizing >25 previously unreported conjugated allenynes—a valuable scaffold in organic synthesis is presented—through copper-catalyzed homocoupling of propargylic esters. This approach utilizes ball milling to activate inexpensive zero-valent copper under solvent-minimized conditions, sourced from both powders and recycled waste materials, including wires and bolts, into catalytically active CuI species under aerobic conditions. The synthetic utility of the synthesized compounds is showcased through an unprecedented rhodium-catalyzed cyclocarbonylation and a gold-catalyzed cyclization reaction
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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