Isocyanides are diverse C1 building blocks considering their potential to react with nucleophiles, electrophiles, and radicals. Therefore, perhaps not surprisingly, isocyanides are highly valuable as inputs for multicomponent reactions (MCRs) and other one‐pot cascade processes. In the field of organometallic chemistry, isocyanides typically serve as ligands for transition metals. The coordination of isocyanides to metal centers alters the electronic distribution of the isocyano moiety, and reaction pathways can therefore be accessed that are not possible in the absence of the metal. The tunable reactivity of the isocyanide functional group by transition metals has evolved into numerous useful applications. Especially palladium‐catalyzed isocyanide insertion processes have emerged as powerful reactions in the past decade. However, reports on the use of earth‐abundant and cheap base metals in these types of transformations are scarce and have received far less attention. In this Minireview, we focus on these emerging base metal catalyzed reactions and highlight their potential in synthetic organic chemistry. Although mechanistic studies are still scarce, we discuss distinct proposed catalytic cycles and categorize the literature according to 1) the (hetero)atom bound to and 2) the type of bonding with the transition metal in which the (formal) insertion occurs. 相似文献
Azacycles such as indoles and tetrahydroquinolines are privileged structures in drug development. Reported here is an unprecedented regiodivergent intramolecular nucleophilic addition reaction of imines as a flexible approach to access N‐functionalized indoles and tetrahydroquinolines, by the control of reaction at the N‐terminus and C‐terminus, respectively. Using ketimines derived from 2‐(2‐nitroethyl)anilines with isatins or α‐ketoesters, the regioselective N‐attack reaction gives N‐functionalized indoles, while the catalytic enantioselective C‐attack reaction affords chiral tetrahydroquinolines featuring an α‐tetrasubstituted stereocenter. Mechanistic studies reveal that hydrogen‐bonding interactions may greatly facilitate such unusual N‐attack reactions of imines. The utility of this protocol is highlighted by the catalytic enantioselective formal synthesis of (?)‐psychotrimine, and the construction of various fused aza‐heterocycles. 相似文献
Twelve naphthochromenone photocatalysts (PCs) were synthesized on gram scale. They absorb across the UV/Vis range and feature an extremely wide redox window (up to 3.22 eV) that is accessible using simple visible light irradiation sources (CFL or LED). Their excited‐state redox potentials, PC*/PC.? (up to 1.65 V) and PC.+/PC* (up to ?1.77 V vs. SCE), are such that these novel PCs can engage in both oxidative and reductive quenching mechanisms with strong thermodynamic requirements. The potential of these bimodal PCs was benchmarked in synthetically relevant photocatalytic processes with extreme thermodynamic requirements. Their ability to efficiently catalyze mechanistically opposite oxidative/reductive photoreactions is a unique feature of these organic photocatalysts, thus representing a decisive advance towards generality, sustainability, and cost efficiency in photocatalysis. 相似文献
Anion‐π catalysis functions by stabilizing anionic transition states on aromatic π surfaces, thus providing a new approach to molecular transformation. The delocalized nature of anion–π interactions suggests that they serve best in stabilizing long‐distance charge displacements. Aiming therefore for an anionic cascade reaction that is as charismatic as the steroid cyclization is for conventional cation‐π biocatalysis, reported here is the anion‐π‐catalyzed epoxide‐opening ether cyclizations of oligomers. Only on π‐acidic aromatic surfaces having a positive quadrupole moment, such as hexafluorobenzene to naphthalenediimides, do these polyether cascade cyclizations proceed with exceptionally high autocatalysis (rate enhancements kauto/kcat >104 m ?1). This distinctive characteristic adds complexity to reaction mechanisms (Goldilocks‐type substrate concentration dependence, entropy‐centered substrate destabilization) and opens intriguing perspectives for future developments. 相似文献
Metallo-ene reactions, hardly recognized until very recently, have experienced a breathtaking development when applied in an intramolecular sense. Efficient regio- and stereoselective magnesium-ene cyclizations have served as a cornerstone for numerous syntheses of structurally diverse natural products (e.g., sesquiterpenes of marine or plant origin, alkaloids, fragrances, insect defense compounds, and a fungitoxin). A brilliant example is the synthesis of the elusive odorant (+)-khusimone which outshines 20 years of work in the field of tricyclovetivane synthesis. Palladium-, platinum-, and nickel-catalyzed versions of the metallo-ene reaction are in a comparatively early stage of exploration, but, nevertheless, reveal intriguing potential. Hence an almost 100% stereospecific C? O→C? ;Pd-→ C? C chirality transfer permits simple and selective, cis- or trans-annelation processes. The mild cyclization conditions are compatible with various functional groups, such as nitrogen moieties, which offer interesting perspectives for the preparation of heterocycles (e.g., alkaloids) difficult to obtain by other methods. Carbon monoxide insertion reactions of the cyclized σ-metal intermediates were shown to afford annelated cyclopentanones and cyclopentenones with concomitant stereocontrolled formation of four carbon–carbon bonds. These and other observations, highlighted in this article, provide a platform for further extensions and applications of this powerful method in organic synthesis. 相似文献
A non‐targeted, ultra‐high‐resolution mass spectrometric, direct analysis of oak‐wood extracts from two species (Quercus robur L. and Quercus petraea Liebl.) from three French forests, and of a wine aged in barrels derived therefrom has been performed to identify families of metabolites that could discriminate both the species and the geographical origin of woods. From 12 T ultra‐high‐resolution Fourier transform ion cyclotron resonance mass spectra of wood extracts, hundreds of mass signals were identified as possible significant biomarkers of the two species, with phenolic and carbohydrate moieties leading the differentiation between Q. robur and Q. petraea, respectively, as corroborated by both FTMS and NMR data. For the first time, it is shown that oak woods can also be discriminated on the basis of hundreds of forest‐related compounds, and particular emphasis is put on sessile oaks from the Tronçais forest, for which sugars are significantly discriminant. Despite the higher complexity and diversity of wine metabolites, forest‐related compounds can also be detected in wines aged in related barrels. It is only by using these non‐targeted analyses that such innovative results, which reveal specific chemodiversities of natural materials, can be obtained. 相似文献
InBr 3 promotes the addition of ketene silyl acetals to monosubstituted alkynes to afford 2,2‐disubstituted alkenylindium compounds in high regio‐ and stereoselectivity (see scheme). In addition, the alkenylindium derivatives have been subsequently coupled with iodobenzene in the presence of a palladium catalyst.
Going through the phases : The title reaction was found to proceed by an initial base‐mediated isomerization to allenyl esters and subsequent phase transfer catalyzed alkylation at the α position of the ester (see scheme).
Theoretically speaking : The mechanistic details associated with the generation and reaction of [CuO]+ species from CuI–α‐ketocarboxylate complexes, especially with respect to modifications of the ligand supporting the copper center, were investigated (see scheme). Theoretical models were used to characterize the electronic structures of different [CuO]+ species and their reactivity in C? H activation and O‐atom transfer reactions.
