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Catalysts
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Heteroaromatic N-oxides in Synthesis and Asymmetric Catalysis
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Heteroaromatic N-oxides in Synthesis and Asymmetric Catalysis

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Catalysis in Organic and Polymer Chemistry".

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 8983

Special Issue Editor

Dr. Renata Siedlecka

E-Mail Website
Guest Editor
Faculty of Chemistry, Department of Organic and Medical Chemistry, Wroclaw University of Science and Technology, Wyspianskiego 27, 50-370 Wroclaw, Poland
Interests: organic synthesis; chemo-, diastereo-, and enantioselective reactions; synthesis of chiral compounds in enantiomeric form and using them as a source of asymmetric induction in catalytic reactions; preparation of heteroaromatic compounds and their N-oxides and their catalytic applications

Special Issue Information

Dear Colleagues,

The design of catalytic processes applying transition metal-free methodologies remains an important task in organic synthesis. An observed increasing interest in chiral N-oxides can be explained by their numerous advantages, including their cost-effectiveness, low environmental harmfulness, and stability in air. The nucleophilicity of the oxygen atom in N-oxides, coupled with a high affinity of silicon to oxygen, represent ideal properties for the development of synthetic methodology based on nucleophilic activation of organosilicon reagents. Their application as catalysts has attracted considerable attention since Nakajima’s report (1998) regarding the asymmetric allylation of aldehydes with allyltrichlorosilanes. However, their usefulness in catalytic ring-opening of meso-epoxides, propargylation, allenylation, aldol reaction, and reduction in ketoimines has also been proven. The demand for asymmetric induction in the aforementioned as well as other reactions has motivated researchers to look for chiral N-oxides as organocatalysts. Chiral heteroaromatic N-oxides can work as powerful electron-pair donors, providing suitable electronic environments in the transition state formed within the reaction. This has resulted in a significant increase in interest in the methods of their preparation and their different applications in asymmetric synthesis. The efficiency of both chiral N-oxides and N,N’-dioxides is a topic of debate, as the superiority of sometimes the former and sometimes the latter is touted frequently. A disadvantage of many of the described, albeit effective, catalysts is usually their multi-stage, tedious preparation process. Thus, there is still a need for chiral N-oxides with a simple structure, which are easy to obtain but have at least comparable stereo-differentiating abilities. Scientists now have a wide range of tools for the creation of the desired spatial arrangement of the molecule, but the point is often simplicity. Catalytic applications are of course an additional aspect of the well-documented importance of N-oxides in the planning of the synthesis of substituted azaaromatic systems.

Dr. Renata Siedlecka
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Catalysts is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • heteroaromatic compounds
  • N-oxides
  • Lewis-base properties
  • organocatalysts
  • asymmetric synthesis
  • stereoselectivity
  • enantioenrichment

Published Papers (4 papers)

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Research

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17 pages, 1588 KiB  
Article
Synthesis and Selected Transformations of 2-Unsubstituted Imidazole N-Oxides Using a Ball-Milling Mechanochemical Approach
by Grzegorz Mlostoń, Małgorzata Celeda, Heinz Heimgartner, Damian Duda, Emilia Obijalska and Marcin Jasiński
Catalysts 2022, 12(6), 589; https://doi.org/10.3390/catal12060589 - 28 May 2022
Cited by 6 | Viewed by 2037
Abstract
Synthetically relevant 2-unsubstituted imidazole N-oxides were obtained by using the ball-milling mechanochemical method. The presented approach extended the scope of the known method and enabled the preparation of hitherto little known N(1)-aryl-substituted derivatives, which are of interest as starting materials for [...] Read more.
Synthetically relevant 2-unsubstituted imidazole N-oxides were obtained by using the ball-milling mechanochemical method. The presented approach extended the scope of the known method and enabled the preparation of hitherto little known N(1)-aryl-substituted derivatives, which are of interest as starting materials for the synthesis of more complex imidazole-based organic materials, generally in good to excellent yields. In addition, selected one-pot mechanochemical transformations including N- and O-alkylations as well as sulfur transfer reactions based on either (3+2)-cycloaddition reaction with 2,2,4,4-tetramethylcyclobutane-1,3-dithione or sulfurization of the transient imidazol-2-ylidenes, generated from corresponding imidazolium salts, were studied. The reported results can be considered as a continuation of long-term studies focused on the synthesis and applications of 2-unsubstituted imidazole N-oxides. Full article
(This article belongs to the Special Issue Heteroaromatic N-oxides in Synthesis and Asymmetric Catalysis)
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10 pages, 1755 KiB  
Article
Diastereoselective Formation of Quaternary Stereocenters in Imidazole N-Oxide Cycloaddition with Fluoroalkenes
by Patrycja Bukowska and Rafał Loska
Catalysts 2022, 12(2), 177; https://doi.org/10.3390/catal12020177 - 29 Jan 2022
Viewed by 2116
Abstract
Imidazole N-oxides are attractive starting materials for the preparation of complex molecules containing an imidazole ring. Dipolar cycloaddition between 1,1-difluoroalkenes and imidazole N-oxides bearing a chiral auxiliary performed in the presence of oxygen or nitrogen nucleophiles was found to provide access [...] Read more.
Imidazole N-oxides are attractive starting materials for the preparation of complex molecules containing an imidazole ring. Dipolar cycloaddition between 1,1-difluoroalkenes and imidazole N-oxides bearing a chiral auxiliary performed in the presence of oxygen or nitrogen nucleophiles was found to provide access to esters and amides bearing a 2-azaheteroaryl substituent at the α position of the imidazole ring as mixtures of diastereomers that, in most cases, are readily separable. This three-component reaction introduces a new tertiary or quaternary all-carbon stereocenter into the heterocyclic ring at a position originally occupied by hydrogen. Importantly, products containing a trifluoromethyl group attached to this stereocenter are readily available as well. Full article
(This article belongs to the Special Issue Heteroaromatic N-oxides in Synthesis and Asymmetric Catalysis)
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9 pages, 2415 KiB  
Article
Steps toward Rationalization of the Enantiomeric Excess of the Sakurai–Hosomi–Denmark Allylation Catalyzed by Biisoquinoline N,N’-Dioxides Using Computations
by Pierpaolo Morgante, Coty Deluca, Tegla E. Jones, Gregory J. Aldrich, Norito Takenaka and Roberto Peverati
Catalysts 2021, 11(12), 1487; https://doi.org/10.3390/catal11121487 - 04 Dec 2021
Viewed by 2154
Abstract
Allylation reactions of aldehydes are chemical transformations of fundamental interest, as they give direct access to chiral homoallylic alcohols. In this work, we focus on the full computational characterization of the catalytic activity of substituted biisoquinoline-N,N’-dioxides for the allylation of 2-naphthaldehyde. We characterized [...] Read more.
Allylation reactions of aldehydes are chemical transformations of fundamental interest, as they give direct access to chiral homoallylic alcohols. In this work, we focus on the full computational characterization of the catalytic activity of substituted biisoquinoline-N,N’-dioxides for the allylation of 2-naphthaldehyde. We characterized the structure of all transition states as well as identified the π stacking interactions that are responsible for their relative energies. Motivated by disagreement with the experimental results, we also performed an assessment of 34 different density functional methods, with the goal of assessing DFT as a general tool for understanding this chemistry. We found that the DFT results are generally consistent as long as functionals that correctly account for dispersion interactions are used. However, agreement with the experimental results is not always guaranteed. We suggest the need for a careful synergy between computations and experiments to correctly interpret the data and use them as a design tool for new and improved asymmetric catalysts. Full article
(This article belongs to the Special Issue Heteroaromatic N-oxides in Synthesis and Asymmetric Catalysis)
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Review

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26 pages, 8885 KiB  
Review
Selectivity in the Aliphatic C–H Bonds Oxidation (Hydroxylation) Catalyzed by Heme- and Non-Heme Metal Complexes—Recent Advances
by Renata Siedlecka
Catalysts 2023, 13(1), 121; https://doi.org/10.3390/catal13010121 - 05 Jan 2023
Cited by 3 | Viewed by 2148
Abstract
The oxyfunctionalization of non-activated C-H bonds has attracted considerable attention for several years. Following the example of enzymatic systems, a multitude of catalytic systems capable of carrying out such a transformation efficiently and selectively have been described. The great discoveries in this area [...] Read more.
The oxyfunctionalization of non-activated C-H bonds has attracted considerable attention for several years. Following the example of enzymatic systems, a multitude of catalytic systems capable of carrying out such a transformation efficiently and selectively have been described. The great discoveries in this area were described at the beginning of the 21st century, but due to the growing demand for precise syntheses (e.g., for the needs of the pharmaceutical industry), new solutions or new applications for already known catalytic systems are constantly being sought. This review article summarizes the development of metal complex-catalyzed selective functionalization of saturated C-H bonds since 2010. However, brief references to previous studies are also made for clarity. There is a huge amount of literature reports in this area, so we intend to highlight only the most important findings in the selective hydroxylation of saturated C–H bonds. Their practical applications in synthesis will also be pointed out. Full article
(This article belongs to the Special Issue Heteroaromatic N-oxides in Synthesis and Asymmetric Catalysis)
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