First reported less than a decade ago, the α,β-unsaturated acyl azolium has emerged as a central reactive intermediate for reaction discovery using N-heterocyclic carbene catalysis. In this ...Perspective, an introduction to the four main reactivity patterns accessible from this intermediate is provided. The Perspective is handled in a largely chronological fashion, with an emphasis on alternate approaches to the key intermediate and first-in-class reaction cascades. Finally, a brief discussion of emerging trends in this field of catalysis is presented. Although not exhaustive, the Perspective provides an overview of this active area of research and serves as a guide for future investigations.
Abstract
A method for conducting enantioselective bromolactonization reactions of trisubstituted alkenoic acids, using the
C
3
‐symmetric trisimidazoline
1
and 1,3‐dibromo‐5,5‐dimethyl hydantoin as a ...bromine source, has been developed. The process generates chiral δ‐lactones that contain a quaternary carbon. The results of studies probing geometrically different olefins show that (
Z
)‐olefins rather than (
E
)‐olefins are favorable substrates for the process. The method is not only applicable to acyclic olefin reactants but can also be employed to transform cyclic trisubstituted olefins into chiral spirocyclic lactones. Finally, the synthetic utility of the newly developed process is demonstrated by its application to a concise synthesis of tanikolide, an antifungal marine natural product.
The Front Cover shows like the fungi, the organocatalytic multi‐catalytic one‐pot method also stands as a unique kingdom in the field of synthetic organic chemistry by simply making the impossible ...possible. We sincerely thank Mr. A. Vamshi Krishna, Ms. Revoju Sravanthi and Mr. Raghu Ghanapuram for the excellent cover design. More information can be found in the Research Article by D. B. Ramachary et al.
σ‐Hole Interactions in Catalysis Breugst, Martin; Koenig, Jonas J.
European journal of organic chemistry,
September 14, 2020, Letnik:
2020, Številka:
34
Journal Article
Recenzirano
Odprti dostop
Noncovalent interactions like halogen, chalcogen, and pnictogen bonding are known for a very long time. During the last decade, these interactions have found different applications in catalysis. ...These forces are often called σ‐hole interactions which can be explained by the anisotropic distribution of the electron density around these atoms. In this MiniReview, we will present recent applications of halogen, chalcogen, and pnictogen bonding in catalysis and discuss experimental and computational investigations to gain more insights into the underlying mechanisms.
This minireview summarizes the recent applications of halogen, chalcogen, and pnictogen bonding in organocatalysis. In all these cases, a Lewis‐acidic region around an element of group 15–17 (the so‐called σ‐hole) interacts with the electron pair of a suitable Lewis base. Besides a discussion of recent applications, this review focuses on mechanistic investigations and comparisons between the different σ‐hole interactions.
Squaramides are presented as modular, easy to optimize, and effective catalysts for the conversion of epoxides and carbon dioxide into cyclic organic carbonates (COCs). The catalytic potential of ...these squaramides, in combination with a suitable halide nucleophile, is particularly noted when internal epoxides are examined as substrates, and their transformation into disubstituted COCs marks a rare case of an effective organocatalyst for these challenging conversions. Control experiments support the mechanistic view that the squaramides are predominantly involved in the stabilization of intermediate oxo and carbonato anions which, after their formation, are able to displace a bromide nucleophile from an initially formed 1:1 assembly comprising the squaramide host.
Centratherin is a sesquiterpene lactone that has the potential to inhibit target proteins for cancer therapy, such as the inflammatory mediator NF-κB. Indoles also exhibit antitumoral activity and ...can modulate the NF-κB signaling pathway. Here we describe a molecular-docking guided semi-synthesis of indole-containing centratherin derivatives. In silico studies indicated that these compounds have high affinity to NF-κB and do not present toxicity or carcinogenicity. Two enantiomeric series of indole-centratherin hybrids were synthesized in three steps with good yields and ee, employing an organocatalyzed Friedel-Crafts alkylation as a key step. The compounds were evaluated against human leukemia K562 cells and showed promising antitumoral activities with IC50 ranging from 0.49 to 7.83 μM.
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•Centratherin is a sesquiterpene lactone potentially inhibiting target proteins for cancer therapy, including NF-κB.•Indoles demonstrate antitumoral activity and can modulate the NF-κB signaling pathway.•Molecular-docking guided semi-synthesis of indole-centratherin hybrids is described using organocatalyzed Friedel-Crafts alkylation as a key step.•The compounds exhibited promising antitumoral activities against K562 cells with IC50 ranging from 0.49 to 7.83 μM.
The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing both axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted ...3,3′‐bisindoles with 3‐indolylmethanols (up to 98 % yield, all >95:5 d.r., >99 % ee). This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles. This reaction not only provides a good example for simultaneously controlling axial and central chirality in one operation, but also serves as a new strategy for catalytic enantioselective construction of axially chiral 3,3′‐bisindole backbones from prochiral substrates.
Bulk up: The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted 3,3′‐bisindoles with electrophiles. This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles.
On the sunny side: Recent examples of visible‐light‐promoted photoredox catalysis in the presence of Ru(bpy)32+ as an efficient photocatalyst have set new standards for conducting challenging ...reactions under mild and environmentally benign conditions.
Axial chirality widely exists in natural products, pharmaceutical compounds, and other functional molecules; these axially chiral compounds also find wide utility as catalysts or ligands in organic ...synthetic chemistry. Nevertheless, whereas significant progress has been made toward the synthesis of enantioenriched axially chiral molecules over the past two decades, the strategies involving organocatalysis have only started to emerge recently. N-heterocyclic carbene (NHC) organocatalysts have been recognized to be powerful tools for the rapid construction of complex molecular architectures. However, previous works have mainly focused on the assembly of point chirality and only recently has it been realized that the asymmetric synthesis of axial chirality could be achieved by using NHCs as organocatalysts. This Perspective highlights the developments and advances in the synthesis of axially chiral scaffolds catalyzed by NHCs. The aim of this Perspective is to provide an overview of this area and serve as a stepping stone for future investigations.
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