1,721,042 research outputs found
Recent Progress in Decarboxylative Oxidative Cross-Couplings for Biaryl Synthesis
No full textThe beginning of the 21st century has seen a tremendous growth in the field of decarboxylative activation. Benzoic acids are now recognised as atom-economicalternatives to traditional cross-coupling partners and they also benefit from being inexpensive, readily-available and shelfstable reagents. In this microreview, we discuss recent developments in the coupling of benzoic acids with either anarene or a second benzoic acid, a process often labelled as decarboxylative oxidative cross-coupling. These procedures hold great promise for the development of highly selective and atom-economic cross-couplings
Decarboxylative Suzuki-Miyaura Coupling of (hetero)aromatic carboxylic acids using Iodine as the Terminal Oxidant
Full text linkA novel methodology for the decarboxylative Suzuki-Miyaura-type coupling has been established. This process uses iodine or a bromine source as both the decarboxylation mediator and the terminal oxidant, thus avoiding the need for stoichiometric amounts of transition metal salts previously required. Our new protocol allows for the construction of valuable biaryl architectures through the coupling of (hetero)aromatic carboxylic acids with arylboronic acids. The scope of this decarboxylative Suzuki reaction has been greatly diversified, allowing for previously inaccessible non-ortho-substituted aromatic acids to undergo this transformation. The procedure also benefits from low catalyst loadings and the absence of stoichiometric transition metal additives
Carboxylic acid salts as dual-function reagents for Carboxylation and Carbon Isotope labeling
No full textThe potassium salts of carboxylic acids are developed as efficient carboxylating agents through CO2 exchange. We describe these carboxylates as dual-function reagents because they function as a combined source of CO2 and base/metalating agent. By using the salt of a commercially available carboxylic acid, this protocol overcomes difficulties when using CO2 gas or organometallic reagents, such as pressurized containers or strictly inert conditions. The reaction proceeds under mild conditions, does not require transition metals or other additives, and shows broad substrate scope. Through the preparation of several biologically important molecules, we show how this strategy provides an opportunity for isotope labeling with low equivalents of labeled CO2
Selective and general exhaustive cross-coupling of di-chloroarenes with a deficit of nucleophiles mediated by a Pd–NHC complex
No full textWe report the first example of a general, exhaustive Pd-mediated cross-coupling of polychloroarenes in the presence of a deficit of nucleophiles, mediated by the highly active PEPPSI-IPent catalyst. Our results indicate that this catalyst system may be applicable to the pseudo-living polymerisation of chloroarene monomer
A silver-free system for the direct C-H auration of arenes and heteroarenes from gold chloride complexes
No full textA new methodology for the direct C-H auration of electron-deficient arenes and heteroarenes with simple bases and readily available [Au(PR3)Cl] complexes is described. This system allows the preparation of a wide scope of aryl-Au(i) compounds without the need for using Ag(i) additives or preparing and isolating basic Au(i) hydroxide complexes.</p
Transition Metal-Free Decarboxylative Iodination:New Routes for Decarboxylative Oxidative Cross-Couplings
No full textConstructing products of high synthetic value from inexpensive and abundant starting materials is of great importance. Aryl iodides are essential building blocks for the synthesis of functional molecules and efficient methods for their synthesis from chemical feedstocks are highly sought after. Here we report a low-cost decarboxylative iodination that occurs simply from readily available benzoic acids and I2. The reaction is scalable and the scope and robustness of the reaction is thoroughly examined. Mechanistic studies suggest that this reaction does not proceed via a radical mechanism, which is in contrast to classical Hunsdiecker-type decarboxylative halogenations. In addition, DFT studies allow comparisons to be made between our procedure and current transition metal-catalyzed decarboxylations. The utility of this procedure is demonstrated in its application to oxidative cross-couplings of aromatics via decarboxylative/C–H or double decarboxylative activations that use I2 as the terminal oxidant. This strategy allows the preparation of biaryls previously inaccessible via decarboxylative methods and holds other advantages over existing decarboxylative oxidative couplings as stoichiometric transition metals are avoided
The use of carboxylic acids as traceless directing groups for regioselective C-H bond functionalisation
No full textThe ability to selectively functionalise a specific C-H bond is a long-standing challenge due to the ubiquity of such bonds in organic molecules. One of the most common approaches to overcome this obstacle consists of installing directing groups into substrates to direct the functionalisation towards the desired C-H bond, leaving behind the directing group in the molecule. Alternatively, carboxylic acids have been employed as traceless directing groups that are easily removed after carboxylic acid-directed installation of the desired functionality. This review focuses on the development of this concept and its application to organic synthesis during the last decade.</p
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
- …
