Interest in homogeneous gold catalysis has undergone a marked increase. As strong yet air- and moisture-tolerant π-acids, cationic gold(
i
) complexes have been shown to catalyze diverse ...transformations of alkenes, alkynes and allenes, opening new opportunities for chemical synthesis. The development of efficient asymmetric variants is required in order to take full advantage of the preparative potential of these transformations. During the last few years, the chemical community has achieved tremendous success in the area. This review highlights the updated progress (2011-2015) in enantioselective gold catalysis. The discussion is classified according to the π-bonds activated by gold(
i
), in an order of alkynes, allenes and alkenes. Other gold activation modes, such as σ-Lewis acid catalyzed reactions and transformations of diazo compounds are also discussed.
This review highlights advances in enantioselective gold catalysis over the past five years.
New methods for preparation of tailor-made fluorine-containing compounds are in extremely high demand in nearly every sector of chemical industry. The asymmetric construction of quaternary C–F ...stereogenic centers is the most synthetically challenging and, consequently, the least developed area of research. As a reflection of this apparent methodological deficit, pharmaceutical drugs featuring C–F stereogenic centers constitute less than 1% of all fluorine-containing medicines currently on the market or in clinical development. Here we provide a comprehensive review of current research activity in this area, including such general directions as asymmetric electrophilic fluorination via organocatalytic and transition-metal catalyzed reactions, asymmetric elaboration of fluorine-containing substrates via alkylations, Mannich, Michael, and aldol additions, cross-coupling reactions, and biocatalytic approaches.
New direction: Changes in the ligand structure divert the reactivity of vanadium(V) oxo complexes from alcohol oxidation to a novel non‐oxidative CO bond cleavage. Thus, highly functionalized aryl ...enones can be selectively generated from lignin model compounds by vanadium‐catalyzed cleavage of the β‐O‐4 linkage (see scheme; N blue, O red).
Recent advances related to catalytic enantioselectice fluorination are examined. Catalytic enantioselective monofluoromethylation and catalytic enantioselective difluoromethylation are among the ...topics discussed.
With its impressive features, gold has led to completely new reaction types in recent years, which in turn have strongly influenced both organic catalysis and material science. Other fields where a ...significant amount of new results has been obtained include nanotechnology, self assembly/supramolecular systems and biochemical/medicinal chemistry. As a result, gold is one of the hottest topics in catalysis at the moment, with an increasing amount of research being carried out in this field. While focusing on homogeneous catalysis, this monograph also covers the main applications in heterogeneous catalysis. Following a look at the gold-catalyzed addition of heteroatom nucleophiles to alkynes, it goes on to discuss gold-catalyzed additions to allenes and alkenes, gold-catalyzed benzannulations, cycloisomerization and rearrangement reactions, as well as oxidation and reduction reactions. The whole is finished off with a section on gold-catalyzed aldol and related reactions and the application of gold-catalyzed reactions to natural product synthesis. Of interest to synthetic chemists and inorganic chemists, as well as organic chemists working in homogeneous catalysis, physical and technical chemists.
A self-assembled supramolecular complex is reported to catalyze alkyl-alkyl reductive elimination from high-valent transition metal complexes such as gold(III) and platinum(IV), the central ...bond-forming elementary step in many catalytic processes. The catalytic microenvironment of the supramolecular assembly acts as a functional enzyme mimic, applying the concepts of enzymatic catalysis to a reactivity manifold not represented in biology. Kinetic experiments delineate a Michaelis-Menten-type mechanism, with measured rate accelerations (Kcat/Kuncat)up to 1.9 × 10⁷ (here Kcat and Kuncat are the Michaelis-Menten enzymatic rate constant and observed uncatalyzed rate constant, respectively). This modality has further been incorporated into a dual catalytic cross-coupling reaction, which requires both the supramolecular microenvironment catalyst and the transition metal catalyst operating in concert to achieve efficient turnover.
The development of a gold(III) catalyzed direct enantioconvergent 1,5-enyne cycloisomerization and kinetic resolution reaction is described. The transformation results in highly enantioenriched ...bicyclo3.1.0hexenes at all levels of conversion, with no racemization or symmetrization taking place during the course of the reaction, and simultaneously affords optically enriched 1,5-enynes. This report marks the first highly enantioselective transformation catalyzed by a well-defined cationic gold(III) catalyst and demonstrates the unique potential of gold(III) complexes in enantioselective catalysis.
Transition-metal catalysts containing gold present new opportunities for chemical synthesis, and it is therefore not surprising that these complexes are beginning to capture the attention of the ...chemical community. Cationic phosphine-gold(i) complexes are especially versatile and selective catalysts for a growing number of synthetic transformations. The reactivity of these species can be understood in the context of theoretical studies on gold; relativistic effects are especially helpful in rationalizing the reaction manifolds available to gold catalysts. This Review draws on experimental and computational data to present our current understanding of homogeneous gold catalysis, focusing on previously unexplored reactivity and its application to the development of new methodology.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The palladium‐catalyzed defluorinative coupling of 1‐aryl‐2,2‐difluoroalkenes with boronic acids is described. Broad functional‐group tolerance arises from a redox‐neutral process by a palladium(II) ...active species which is proposed to undergo a β‐fluoride elimination to afford the products. The monofluorostilbene products were formed with excellent diastereoselectivity (≥50:1) in all cases, and it is critical, as traditional chromatographic techniques often fail to separate monofluoroalkene isomers. As a demonstration of this method's unique combination of reactivity and functional‐group tolerance, a Gleevec® analogue, using a monofluorostilbene as an amide isostere, was synthesized.
In neutral: Monofluorostilbenes were prepared by palladium‐catalyzed defluorinative coupling of 1‐aryl‐2,2‐difluoroalkenes with boronic acids. A redox‐neutral process via a palladium(II) species that undergoes a β‐fluoride elimination to afford the products is proposed. Broad functional‐group tolerance arises from the mild reaction conditions and mechanistically distinct reaction manifold. TFA=trifluoroacetate.
During the past decade, the use of Au(I) complexes for the catalytic activation of C–C π-bonds has been investigated intensely. Over this time period, the development of homogeneous gold catalysis ...has been extraordinarily rapid and has yielded a host of mild and selective methods for the formation of carbon–carbon and carbon–heteroatom bonds. The facile formation of new bonds facilitated by gold naturally led to efforts toward rendering these transformations enantioselective. In this Account, we survey the development of catalysts and ligands for enantioselective gold catalysis by our research group as well as related work by others. We also discuss some of our strategies to address the challenges of enantioselective gold(I) catalysis. Early on, our work with enantioselective gold-catalyzed transformations focused on bis(phosphinegold) complexes derived from axially chiral scaffolds. Although these complexes were highly successful in some reactions like cyclopropanation, the careful choice of the weakly coordinating ligand (or counterion) was necessary to obtain high levels of enantioselectivity for the case of allene hydroamination. These counterion effects led us to use the anion itself as a source of chirality, which was successful in the case of allene hydroalkoxylation. In general, these tactics enhance the steric influence around the reactive gold center beyond the two-coordinate ligand environment. The use of binuclear complexes allowed us to use the second gold center and its associated ligand (or counterion) to exert a further steric influence. In a similar vein, we employed a chiral anion (in place of or in addition to a chiral ligand) to move the chiral information closer to the reactive center. In order to expand the scope of reactions amenable to enantioselective gold catalysis to cycloadditions and other carbocyclization processes, we also developed a new class of mononuclear phosphite and phosphoramidite ligands to supplement the previously widely utilized phosphines. However, we needed to judiciously design the steric environment to create “walls” that enclose the gold center. We also successfully applied these same considerations to the development of binuclear carbene ligands for gold. Finally, we describe the design of bifunctional urea–monophosphine ligands used in a gold-catalyzed three-component coupling.
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