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Chemistry of Heterocycles
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Chemistry of Heterocycles

A special issue of Organics (ISSN 2673-401X).

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 9646

Special Issue Editors

Dr. Aneta Wróblewska

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Guest Editor
Centre of Molecular and Macromolecular Studies of the Polish Academy of Sciences, Lodz, Poland
Interests: mechanosynthesis; peptide synthesis; imidazole chemistry
Dr. Mar Ríos-Gutiérrez

E-Mail Website
Guest Editor
Department of Organic Chemistry, University of Valencia (UV), Burjassot, 46100 Valencia, Spain
Interests: Molecular Electron Density Theory (MEDT); physical-organic chemistry; chemical concepts and reactivity; molecular mechanisms; reaction selectivities; pseudocyclic reactions; chemical bond and chemical structure; conceptual DFT; Quantum Topology of electron distribution functions such as electron density and electron localization function (ELF)
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Radomir Jasiński

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Guest Editor
Department of Organic Chemistry & Technology, Cracow University of Technology, Warszawska 24, 31-155 Krakow, Poland
Interests: cycloaddition reactions; nitrocompounds; cycloaddition; heterocycles; reaction mechanisms; organic reactivity; DFT calculations
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue will cover the most recent trends in the chemistry of heterocyclic compounds. In particular, we invite researchers to publish their recent short laboratory notes and full papers regarding the synthesis of heterocycles and their properties (including the transformation of the heterocyclic system as well as its functionalization), structural studies, as well as theoretical considerations based on the analysis of electron density applied to synthetic aspects, reaction mechanisms, and structural analysis. Review articles by experts in the field will also be welcome.

Dr. Aneta Wróblewska
Dr. Mar Ríos-Gutiérrez
Prof. Dr. Radomir Jasiński
Guest Editors

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. Organics is an international peer-reviewed open access quarterly 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 1000 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

  • Synthesis and transformation of heterocycles
  • Cycloaddition reactions
  • Structural chemistry
  • Biological activity of heterocyclic compounds
  • Molecular electron density theory (MEDT)

Published Papers (5 papers)

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Research

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9 pages, 1162 KiB  
Article
Reinvestigation of the Room Temperature Photochemical Reaction between N-Methyl-1,2,4-triazoline-3,5-dione (MeTAD) and Benzene
by Gary W. Breton
Organics 2023, 4(2), 164-172; https://doi.org/10.3390/org4020013 - 17 Apr 2023
Viewed by 1070
Abstract
The photochemical reaction of N-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with benzene is known to lead to a Diels–Alder cycloaddition product when conducted at low temperatures (i.e., <−60 °C). This reactivity has been exploited recently for novel synthetic applications. It was previously reported that no reaction [...] Read more.
The photochemical reaction of N-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with benzene is known to lead to a Diels–Alder cycloaddition product when conducted at low temperatures (i.e., <−60 °C). This reactivity has been exploited recently for novel synthetic applications. It was previously reported that no reaction between MeTAD and benzene occurs at room temperature. However, it has now been discovered that MeTAD reacts effectively with benzene upon visible light irradiation over a several day period at room temperature. The major product is a para-substituted bisurazole adduct. Our studies indicate that the adduct is formed via sequential aromatic substitution reactions made possible by electron transfer from the aromatic ring to the highly electrophilic triplet state of photoactivated MeTAD. Full article
(This article belongs to the Special Issue Chemistry of Heterocycles)
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18 pages, 7770 KiB  
Article
Exploration of the Divergent Outcomes for the Nenitzescu Reaction of Piperazinone Enaminoesters
by Rebecca Hermans, Max Van Hoof, Luc Van Meervelt and Wim Dehaen
Organics 2023, 4(2), 146-163; https://doi.org/10.3390/org4020012 - 07 Apr 2023
Viewed by 1499
Abstract
The Nenitzescu reaction is a condensation reaction between an enamine and a quinone, which can give rise to a wide variety of reaction products depending on the nature of the starting material and the reaction conditions. The most commonly observed products are 5-hydroxyindoles [...] Read more.
The Nenitzescu reaction is a condensation reaction between an enamine and a quinone, which can give rise to a wide variety of reaction products depending on the nature of the starting material and the reaction conditions. The most commonly observed products are 5-hydroxyindoles and 5-hydroxybenzofurans. Both classes are of interest since they are known to possess a variety of promising bioactivities. Despite the high chemodivergency for this reaction, it remains an interesting synthetic strategy thanks to the mild reaction conditions, easily accessible starting materials and simple reaction procedures. For these reasons, our research group investigated the Nenitzescu reaction of piperazinone enaminoesters, resulting in the unexpected formation of rearranged 2-imidazolidinone benzofurans. In this work, we aimed to develop reaction conditions that favor the formation of 5-hydroxyindoles via an extensive, multivariate optimization study. This led to valuable insights into the parameters that influence regio- and chemoselectivity. Furthermore, two novel products were obtained, a pyrrolo[2,3-f]indole and a benzofuranone, both of which are rarely reported in the literature. Full article
(This article belongs to the Special Issue Chemistry of Heterocycles)
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13 pages, 2153 KiB  
Article
Dihydrooxazine Byproduct of a McMurry–Melton Reaction en Route to a Synthetic Bacteriochlorin
by Vy-Phuong Tran, Nobuyuki Matsumoto, Phattananawee Nalaoh, Haoyu Jing, Chih-Yuan Chen and Jonathan S. Lindsey
Organics 2022, 3(3), 262-274; https://doi.org/10.3390/org3030019 - 08 Aug 2022
Cited by 4 | Viewed by 1744
Abstract
A synthetic route to gem-dimethyl-substituted bacteriochlorins—models of native bacteriochlorophylls—relies on the formation of a dihydrodipyrrin precursor via a series of established reactions: van Leusen pyrrole formation, Vilsmeier formylation, Henry reaction, borohydride reduction, Michael addition, and McMurry–Melton pyrroline formation. The latter is the least [...] Read more.
A synthetic route to gem-dimethyl-substituted bacteriochlorins—models of native bacteriochlorophylls—relies on the formation of a dihydrodipyrrin precursor via a series of established reactions: van Leusen pyrrole formation, Vilsmeier formylation, Henry reaction, borohydride reduction, Michael addition, and McMurry–Melton pyrroline formation. The latter is the least known of the series. Here, the McMurry–Melton reaction of a 2-(6-oxo-2-nitrohexyl)pyrrole in the presence of TiCl3 and an ammonium acetate buffer formed the expected Δ1-pyrroline, as well as an unexpected polar, cyclic byproduct (a 5,6-dihydro-4H-1,2-oxazin-6-ol), each attached to the 2-methylpyrrole unit. Both species were characterized by single-crystal X-ray diffraction. The McMurry–Melton reaction is a type of intercepted Nef reaction (the transformation of a nitroalkyl motif into a carbonyl group), where both the Δ1-pyrroline and the dihydrooxazine derive from the reaction of the nitrogen derived from the nitro group upon complete or partial reductive deoxygenation, respectively, with the γ-keto group. The report also considers competing Nef and McMurry–Melton reactions, the nature of available TiCl3 reagents, and the use of ammonium acetate for buffering the TiCl3/HCl reagent. Full article
(This article belongs to the Special Issue Chemistry of Heterocycles)
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15 pages, 3227 KiB  
Article
A Molecular Electron Density Theory Study of the [3+2] Cycloaddition Reaction of Pseudo(mono)radical Azomethine Ylides with Phenyl Vinyl Sulphone
by Mar Ríos-Gutiérrez, Assem Barakat and Luis R. Domingo
Organics 2022, 3(2), 122-136; https://doi.org/10.3390/org3020010 - 06 Jun 2022
Cited by 12 | Viewed by 2200
Abstract
The [3+2] cycloaddition (32CA) reaction of an azomethine ylide (AY), derived from isatin and L-proline, with phenyl vinyl sulphone has been studied within Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) level. ELF topological analysis of AY classifies it as a pseudo(mono)radical [...] Read more.
The [3+2] cycloaddition (32CA) reaction of an azomethine ylide (AY), derived from isatin and L-proline, with phenyl vinyl sulphone has been studied within Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) level. ELF topological analysis of AY classifies it as a pseudo(mono)radical species with two monosynaptic basins at the C1 carbon, integrating a total of 0.76 e. While vinyl sulphone has a strong electrophilic character, AY is a supernucleophile, suggesting a high polar character and low activation energy for the reaction. The nucleophilic Parr functions indicate that the pseudoradical C1 carbon is the most nucleophilic center. The 32CA reaction presents an activation Gibbs free energy of 13.1 kcal·mol−1 and is exergonic by −26.8 kcal·mol−1. This reaction presents high endo stereoselectivity and high meta regioselectivity. Analysis of the global electron density transfer (GEDT) at the most favorable meta/endo TS, 0.31 e, accounts for the high polar character of this 32CA reaction, classified by forward electron density flux (FEDF). A Bonding Evolution Theory (BET) study along the most favorable meta/endo reaction path characterizes this 32CA reaction, taking place through a non-concerted two-stage one-step mechanism, as a pseudo(mono)radical-type 32CA reaction, in agreement with the ELF analysis of the AY. Full article
(This article belongs to the Special Issue Chemistry of Heterocycles)
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Review

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9 pages, 701 KiB  
Review
Diels–Alder Polar Reactions of Azaheterocycles: A Theoretical and Experimental Study
by Carla M. Ormachea, María Nélida Kneeteman and Pedro M. E. Mancini
Organics 2022, 3(2), 102-110; https://doi.org/10.3390/org3020008 - 22 May 2022
Cited by 1 | Viewed by 1568
Abstract
A number of azaheterocycles (pyridines, pyrroles and indoles) have been properly functionalized so that they can act as dienophiles in cycloaddition Diels–Alder processes. This work analyzed the reactive behavior of these molecules through mechanistic analysis and the regioselectivity of the process using computational [...] Read more.
A number of azaheterocycles (pyridines, pyrroles and indoles) have been properly functionalized so that they can act as dienophiles in cycloaddition Diels–Alder processes. This work analyzed the reactive behavior of these molecules through mechanistic analysis and the regioselectivity of the process using computational calculation tools. Based on this knowledge, a study was conducted on the influences of reaction variables, in particular solvent, catalyst and microwave irradiation, to achieve favorable changes—shorter reaction times, more acceptable temperatures and better yields. Theoretical calculations allowed the development of predictive approaches, which were later experimentally corroborated. This analysis allowed us to make reasonable assumptions related to reaction mechanisms, which allowed—through the analysis of corresponding transition states—us to consider such reactions at the boundary between pericyclic and polar processes. Full article
(This article belongs to the Special Issue Chemistry of Heterocycles)
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