1,721,083 research outputs found
Sulfoxide-mediated oxidative cross-coupling of phenols
No full textA metal-free, oxidative coupling of phenols with various nucleophiles, including arenes, 1,3-diketones and other phenols, is reported. Cross-coupling is mediated by a sulfoxide which inverts the reactivity of the phenol partner. Crucially, the process shows high selectivity for cross-versus homo-coupling and allows efficient access to a variety of aromatic scaffolds including biaryls, benzofurans and, through an iterative procedure, aromatic oligomers.</p
Enantio- and diastereoselective synthesis of homopropargyl amines by copper-catalyzed coupling of imines, 1,3-enynes, and diborons
No full textAn efficient, enantio- and diastereoselective, copper-catalyzed coupling of imines, 1,3-enynes, and diborons is reported. The process shows broad substrate scope and delivers complex, chiral homopropargyl amines; useful building blocks on the way to biologically-relevant compounds. In particular, functionalized homopropargyl amines bearing up to three contiguous stereocenters can be prepared in a single step.</p
Para-coupling of phenols with C2/C3-substituted benzothiophene S-oxides
No full textC2 and C3 substituted benzothiophenes are common structures in medicinal and materials chemistry. The cross-coupling of phenols with benzothiophenes is a useful route towards these important molecules. In this report we reveal an efficient C–H/C–H-type cross-coupling of benzothiophenes, activated as their S-oxides, with phenols to give C2/C3 arylated benzothiophenes. Whereas previous reports describe cross-coupling at the ortho-position between phenols and sulfoxides, this procedure allows para-functionalization of phenols that typically have their ortho positions blocked.</p
Copper-Catalyzed Functionalization of 1,3-Dienes: Hydrofunctionalization, Borofunctionalization, and Difunctionalization
No full textThe catalytic conversion of chemical feedstocks into products of medicinal and agricultural value is a key theme across modern synthetic chemistry. As 1,3-dienes are readily available from industrial cracking processes, there is great interest in the development of sustainable methods for the functionalization of these simple molecules. Although initial developments in this field have required precious-transition-metal catalysts, there has been a push toward the use of inexpensive, nontoxic, and more abundant copper catalysts to promote functionalization. This Perspective covers the many developments in the area of copper-catalyzed functionalization of 1,3-dienes, in particular hydrofunctionalization, borofunctionalization, and difunctionalization (e.g., diamination).</p
Metal-free photoredox-catalysed formal C–H/C–H coupling of arenes enabled by interrupted Pummerer activation
No full textAryl–aryl cross-coupling constitutes one of the most widely used procedures for the synthesis of high-value materials that range from pharmaceuticals to organic electronics and conducting polymers. The assembly of (hetero)biaryl scaffolds generally requires multiple steps; coupling partners must be functionalized before the key bond-forming event is considered. The development of selective C–H arylation processes in arenes—which sidestep the need for prefunctionalized partners—is thus crucial for streamlining the construction of these key architectures. Here we report an expedient, one-pot assembly of (hetero)biaryl motifs using photocatalysis and two non-prefunctionalized arene partners. The approach is underpinned by the functionalization of a C–H bond in an arene coupling partner using the interrupted Pummerer reaction. A unique pairing of the organic photoredox catalyst and the intermediate dibenzothiophenium salts enables highly selective reduction in the presence of sensitive functionalities. The utility of the metal-free, one-pot strategy is exemplified by the synthesis of a bioactive natural product and the modification of complex molecules of societal importance.</p
Copper-catalyzed functionalization of enynes
No full textThe copper-catalyzed functionalization of enyne derivatives has recently emerged as a powerful approach in contemporary synthesis. Enynes are versatile and readily accessible substrates that can undergo a variety of reactions to yield densely functionalized, enantioenriched products. In this perspective, we review copper-catalyzed transformations of enynes, such as boro- and hydrofunctionalizations, copper-mediated radical difunctionalizations, and cyclizations. Particular attention is given to the regiodivergent functionalization of 1,3-enynes, and the current mechanistic understanding of such processes. </p
Radical C–C bond formation using sulfonium salts and light
Full text linkSulfonium salts are playing an increasingly significant role in contemporary organic synthesis. In particular, the generation of radicals from sulfonium salts is a fundamental process in Nature and has been the subject of investigation for over 50 years. However, general synthetic methods that use sulfonium salts as radical precursors are rare. The advent of photoredox catalysis has triggered an upsurge of interest in the radical chemistry of sulfonium salts and this review surveys recent applications of aryl and alkyl sulfonium salts in light‐mediated, radical C–C bond formation
Pummerer chemistry of benzothiophene S-oxides: Metal-free alkylation and arylation of benzothiophenes
No full textFunctionalized benzothiophenes are important constructs found in molecules with wide ranging biological activity and in organic materials. An efficient, metal-free approach to C3 and C2 arylated and alkylated benzothiophenes is summarized in this review. The strategy utilizes synthetically unexplored yet readily accessible benzothiophene S-oxides in an interrupted Pummerer/charge accelerated [3,3]-sigmatropic rearrangement cascade process to regioselectively install aryl, allyl or propargyl groups at C3 of benzothiophenes at the expense of C–H bonds. The intermediate sulfonium salts generated after the interrupted Pummerer reaction lack aromaticity and therefore allow the [3,3]-sigmatropic rearrangement, the key C–C bond-forming event, to occur under mild conditions. In addition, a previously unexplored 1,2-migration of substituents in benzothiophenium salts, generated during the cascade process, can be used to access C2 functionalized benzothiophenes
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
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