1,721,027 research outputs found
La via Appia tra Taranto e Brindisi: ricostruzione del percorso e rapporti con il popolamento
No full textil lavoro propone la ricostruzione del percorso della via Appia tra Taranto e Brindisi, attraverso l’analisi delle fonti storiche e archeologiche, cartografiche e aerofotografiche. Esamina quindi i rapporti della strada con i principali centri abitati e con il popolamento dei comprensori attraversati, in particolare di quello brindisino (territorio di Mesagne). I risultati delle indagini topografiche condotte in quest’area permettono di evidenziare lo stretto rapporto esistente tra la strada e le forme di organizzazione e l’assetto economico del territori
Enantioselective Catalytic Synthesis of Inherently Chiral Calixarenes
No full textSince the introduction of the concept of inherent chirality by B & ouml;hmer, an important part of research focused on the asymmetric synthesis of calixarene macrocycles. However, long synthetic procedures and tedious separation strategies hampered the application of this technology in many topics of organic chemistry, including enantioselective molecular recognition and catalysis. Very recently, a new generation of enantioselective catalytic methodologies has been reported, able to provide highly functionalized, inherently chiral calixarenes in a straightforward manner. In this review, we will discuss these new catalytic methods and the versatile properties of such macrocycles that call for potential applications in many areas of science
Iron-Catalyzed C-H Functionalization Processes
No full textIron-catalyzed C-H activation has recently emerged as an increasingly powerful tool for the step-economical transformation of unreactive C-H bonds. Particularly, the recent development of low-valent iron catalysis has set the stage for novel C-H activation strategies via chelation assistance. The low-cost, natural abundance, and low toxicity of iron prompted its very recent application in organometallic C-H activation catalysis. An overview of the use of iron catalysis in C-H activation processes is summarized herein up to May 2016
Weak O-Assistance Outcompeting Strong N,N-Bidentate Directing Groups in Copper Catalyzed C-H Chalcogenation
No full textA copper-mediated C-H chalcogenation of triazoles has been achieved by weak coordination. The user-friendly protocol showed high functional-group tolerance and ample substrate scope, yielding fully substituted 1,2,3-triazoles with complete positional site-selectivity. The C-H selenylation could likewise be achieved by means of copper catalysis. Our findings highlight for the first time that weak O-coordination can outcompete the strong N,N-bidentate coordination mode in C-H functionalization technology
Recent advances with calix[6]- and calix[8]arene organometallic catalysts
No full textCalixarenes represent a fascinating class of macrocycles with several applications in supramolecular chemistry such as synthetic receptors for ion recognition, prototypes of molecular machines and devices and catalysts. In this scenario, larger calix[6]-and calix[8]arenes represent a modular platform to build novel and more efficient organometallic catalysts. Within this digest review, we aim to survey the latest advancements in this area of research including CAC and C-Het bond formations and fundamental inor-ganic transformations such as ammonia production and carbon dioxide reduction. (c) 2022 Elsevier Ltd. All rights reserved
Iron-Catalyzed C-H Alkynylation through Triazole Assistance: Expedient Access to Bioactive Heterocycles
No full textTriazole assistance enabled the first iron-catalyzed C−H alkynylation of arenes, heteroarenes, and alkenes. The modular TAM directing group set the stage for a sequential C−H alkynylation/annulation strategy with ample scope, enabling the iron-catalyzed assembly of isoquinolones, pyridones, pyrrolones, and isoindolinones with high levels of chemo-, site-, and regioselectivity
Expedient Iron-Catalyzed C-H Allylation/Alkylation by Triazole Assistance with Ample Scope
No full textTriazole assistance set the stage for a unified strategy for the iron-catalyzed C-H allylation of arenes, heteroarenes, and alkenes with ample scope. The versatile catalyst also proved competent for site-selective methylation, benzylation, and alkylation with challenging primary and secondary halides. Triazole-assisted C-H activation proceeded chemo-, site-, and diastereo-selectively, and the modular TAM directing group was readily removed in a traceless fashion under exceedingly mild reaction conditionsTriazole assistance set the stage for a unified strategy for the iron-catalyzed C-H allylation of arenes, heteroarenes, and alkenes with ample scope. The versatile catalyst also proved competent for site-selective methylation, benzylation, and alkylation with challenging primary and secondary halides. Triazole-assisted C-H activation proceeded chemo-, site-, and diastereo-selectively, and the modular TAM directing group was readily removed in a traceless fashion under exceedingly mild reaction condition
Iron Photocatalysis for C─H Functionalizations
No full textPhoto-assisted, iron-catalyzed C─H functionalizations represent nowadays a sustainable tool to develop unprecedented transformations, unviable by common catalytic organometallic approaches promoted by transition metals. In fact, the use of this new technology allows for more efficient synthetic transformations by increasing the chemo-, regio- and site-selectivity of the catalysis while reducing the formation of by-products and shortening reaction times. Further, the replacement of precious transition-metals with iron catalysts is highly desiderable for the development of environmentally-friendly synthetic methods. Within this review, we aim to summarize the latest achievements combining the most abundant and safe transition metal in “outer-sphere” C─H functionalization reactions mediated by light for the formation of new C─C and C─Het bonds, including challenging C─N, C─P, C─B and C─S bonds. Particular attention has been directed toward the description of mechanistic aspects of the iron catalysis and the application of the synthetic methods for late-stage C─H functionalizations of polymers, marketed drugs, biologically-active compounds and materials
Palladium/Brønsted Acid Catalysis for Hydrofunctionalizations of Alkynes: From Tsuji-Trost Allylations to Stereoselective Methodologies
Full text linkAlkynes are one of the most abundant feedstocks for chemical
transformations. By merging palladium and Brønsted acid
catalysts, they are converted into reactive allylmetal species,
which become suitable for Tsuji-Trost functionalizations with
complete atom-economy. This approach, which overcomes the
limitations of traditional methods that suffer from the formation
of over-stoichiometric amounts of by-products, has been
disclosed for developing new C-C and C-Het bond forming
methodologies. Within this review, we aim to survey the latest
advancements in this area including applications in polymer
chemistry, deuterium-labeling and stereoselective catalysi
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