1,720,975 research outputs found
Ir-Catalyzed Selective Hydroboration of 2-Substituted 1,3-Dienes: A General Method to Access Homoallylic Boronates
No full textAn operationally simple protocol for the 4,3-selective hydroboration of 2-substituted 1,3-dienes using an iridium catalyst is described. Independently of the nature (alkyl, aryl, heteroaryl) and the size of the substituent in the 2-position, it provides access to a variety of homoallylic boronates featuring a 1,1-disubstituted olefin in high yield and chemo- and regioselectivity. An array of potentially sensitive functional groups is well-tolerated, and the method can be extend to 1,2-disubstituted 1,3-dienes. Derivatization of the homoallylic boronates is also demonstrated using contemporary catalytic and enantioselective processes
Transition metal-catalyzed alkene isomerization as an enabling technology in tandem, sequential and domino processes
Full text linkOne-pot reactions elaborated around transition metal-catalyzed isomerization of alkenes not only offer the inherent advantages of atom-, step-and redox-economy but also enable the preparation of value-Added products that would be difficult to access by conventional methods. In this Review, we cover seminal and recent examples of tandem, sequential and domino processes, which incorporate the most attractive features of olefin isomerization
Introduction (a Chroniques vulciennes, I. De l'age d'or des fouille à la création du service de tutelle des monuments)
No full textIntroduzione al volum
‘Ritorno a Vulci’. New tools for the study of the south-eastern necropolises
No full textThe project ‘Ritorno a Vulci’ focuses on specific sectors of the south-eastern necropolis of Vulci, where excavations have been conducted since the 1800s. One of the primary objectives of this project is to create a dedicated WebGIS that will generate and manage new topographical documentation of the area. This will serve as a collaborative digital research platform, making document consultation more accessible and contributing to their preservation.
Another significant digital project is ‘Vulci nel Mondo’ (VNM), which is conceived as a Virtual Museum. The Authors illustrate this highly versatile tool as an online space to bring together a permanent collection on Vulci. The standard virtual tour model is built on two key aspects: navigation, providing access to the collections and other information on the museum’s website, and interaction, simulating a physical space with which visitors can engage
Exploring Site Selectivity of Iridium Hydride Insertion into Allylic Alcohols: Serendipitous Discovery and Comparative Study of Organic and Organometallic Catalysts for the Vinylogous Peterson Elimination
Full text linkThe vinylogous Peterson elimination of a broad range of primary, secondary, and tertiary silylated allylic alcohols by two distinct and complementary catalytic systems - a cationic iridium complex and a Brønsted acid - is reported. These results are unexpected. Nonsilylated substrates are typically isomerized into aldehydes and silylated allylic alcohols into homoallylic alcohols with structurally related iridium complexes. Although several organic acids and bases are known to promote the vinylogous Peterson elimination, the practicality, mildness, functional group tolerance, and generality of both catalysts are simply unprecedented. Highly substituted C=C bonds, stereochemically complex scaffolds, and vicinal tertiary and quaternary (stereo)centers are also compatible with the two methods. Both systems are stereospecific and enantiospecific. After optimization, a vast number of dienes with substitution patterns that would be difficult to generate by established strategies are readily accessible. Importantly, control experiments secured that traces of acid that may be generated upon decomposition of the in situ generated iridium hydride are not responsible for the activity observed with the organometallic species. Upon inspection of the reaction scope and on the basis of preliminary investigations, a mechanism involving iridium-hydride and iridium-allyl intermediates is proposed to account for the elimination reaction. Overall, this study confirms that site selectivity for [Ir-H] insertion across the C=C bond of allylic alcohols is a key parameter for the reaction outcome
Copper-catalyzed enantioselective 1,2-borylation of 1,3-dienes
No full textA highly enantioselective Cu-catalyzed borylation of 2-substituted 1,3-dienes is reported. The use of a chiral phosphanamine ligand is essential in achieving high chemo-, regio-, diastereo- and enantioselectivity. It provides access to a variety of homoallylic boronates in consistently high yield and enantiomeric excess with 2-aryl and 2-heteroaryl 1,3-dienes as well as sterically demanding 2-alkyl 1,3-dienes. Preliminary investigations based on a non-linear effect study point to a mechanism involving more than one metal center
Remote Functionalization of α,β-Unsaturated Carbonyls by Multimetallic Sequential Catalysis
No full textThe remote functionalization of α,β-unsaturated carbonyls by an array of multimetallic sequential catalytic systems is described. The reactions are triggered by hydrometalation using [Pd-H] or [Ru-H] isomerization catalysts and driven by the formation of thermodynamically more stable 1,2-vinyl arenes. The Pd-catalyzed deconjugative isomerization was combined with a Cu-catalyzed β-borylation of the transiently generated styrenyl derivatives to deliver a range of products that would not be accessible with the use of a single catalyst. [Pd/Cu] catalytic systems were also identified for the highly enantioselective α-hydroboration and α-hydroamination of the styrenyl intermediates. Difunctionalization simultaneously at the benzylic and homobenzylic positions was achieved by combining the isomerization process with Sharpless asymmetric dihydroxylation (SAD) using [Pd/Os] or [Ru/Os] couples. Starting from a simple α,β-unsaturated ester, an isomerization/dihydroxylation/lactonization sequence gave access to a naturally occurring γ-butyrolactone in good yield, with excellent diastereo- and enantioselectivity
Access to Highly Stereodefined 1,4- cis-Polydienes by a [Ni/Mg] Orthogonal Tandem Catalytic Polymerization
Full text linkA [Ni/Mg]-catalyzed orthogonal tandem polymerization has been developed starting from enol phosphates. Initial investigations conducted on branched 1,3-dienes as monomers enabled identification of a Mg-initiated polymerization process leading to 1,4-cis-polydienes. When aryl enol phosphates are used as monomers, the [Ni/Mg]-catalyzed tandem polymerization affords 1,4-cis-polydienes with selectivities up to 99%. Elastomeric or crystalline materials were obtained by simple structural modifications of the monomeric unit. This tandem approach appears as a straightforward and efficient way to enforce diversity and selectivity in diene polymerization while retaining a fair degree of control, just as observed for stepwise systems that are accessible through established time- and manpower-consuming synthetic procedures
Direct Access to Chiral Secondary Amides by Copper-Catalyzed Borylative Carboxamidation of Vinylarenes with Isocyanates
Full text linkA Cu-catalyzed borylative carboxamidation reaction has been developed using vinylarenes and isocyanates. Alkynes, branched 1,3-dienes, and bicyclic alkenes were also found to be competent coupling partners. Using a chiral phosphanamine ligand, an enantioselective variant of this transformation was developed, affording a set of α-chiral amides with unprecedented levels of enantioselectivity. The synthetic utility of the method was demonstrated through a series of representative stereoretentive postcatalytic derivatizations
A General Nickel-Catalyzed Kumada Vinylation for the Preparation of 2-Substituted 1,3-Dienes
No full textThe identification of two nickel(II) precatalysts for the preparation of 2-substituted 1,3-dienes by a Kumada cross-coupling between vinyl magnesium bromide and vinyl phosphates is described. This is noteworthy as engaging only one vinyl derivative in a transition-metal-catalyzed cross-coupling reaction is already reputedly challenging. Salient features of this method are its operational simplicity, the mild reaction conditions, the low catalyst loadings, the short reaction times, its scalability, and the use of stoichiometric quantities of each coupling partner. The tolerance of the two nickel catalysts to an important number of reactive functional groups and their compatibility with structurally complex molecular architectures has been extensively delineated. A Negishi variant of the reaction has been developed for even more sensitive organic functions such as ester or nitrile. Several other conjugated 1,3-dienes with various substitution patterns have been prepared by combining commercial alkenyl Grignard reagents and/or readily available alkenyl enol phosphates. Proper choice of the nickel catalyst and the reaction temperature gave access to a variety of different olefin isomers with high levels of stereocontrol. Overall, this approach affords conjugated dienes that would not be accessible otherwise and therefore provides a valuable complement to existing methods
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