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Cyclization Reactions in Organic Synthesis: Recent Developments

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: 31 December 2024 | Viewed by 4340

Special Issue Editors


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Guest Editor
University of Coimbra, Coimbra Chemistry Centre-Institute of Molecular Sciences (CQC-IMS), Department of Chemistry, Coimbra, Portugal
Interests: organic synthesis; heterocyclic chemistry; cycloaddition reactions; allenes; 2H-azirines; mecanochemistry

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Guest Editor
Department of Chemistry, Coimbra Chemistry Centre–Institute of Molecular Sciences, University of Coimbra, 3004-535 Coimbra, Portugal
Interests: organic synthesis; heterocyclic chemistry; medicinal chemistry; oxygen heterocycles; allenes; cycloaddition reactions; annulation reactions; flash vacuum pyrolysis
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Special Issue Information

Dear Colleagues,

Cyclization reactions are a powerful tool in organic synthesis for the construction of cyclic compounds, which present a wide variety of applications in several areas, such as drug discovery, agrochemicals, and materials science.

One of the most significant advantages of these transformations is the ability to generate molecular complexity with high stereochemical control, a crucial feature in the synthesis of natural products and in the pharmaceutical industry. Additionally, these processes enable the synthesis of complex structures with specific ring sizes and shapes, including strained rings, which are difficult to obtain otherwise. Moreover, they often require fewer steps and reagents compared to the classical synthetic methods, resulting in less waste generation and a reduction in the environmental impact, in line with the principles of green chemistry.

In recent decades, cyclization reactions have become increasingly important in organic synthesis and have contributed to the development of novel bioactive compounds, agrochemicals, and polymers, as well as new synthetic routes to natural products.

This Special Issue, “Cyclization Reactions in Organic Synthesis: Recent Developments”, aims to gather the most recent advances on this topic. Full papers, communications, and reviews are all welcome for submission.

Dr. Ana L. Cardoso
Dr. Maria Isabel L. Soares
Guest Editors

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Keywords

  • cyclization reactions
  • radical cyclization
  • cascade reaction
  • asymmetric cyclization
  • cycloaddition reactions
  • carbocyclic compounds
  • heterocyclic compounds
  • bioactive compounds

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Published Papers (4 papers)

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Research

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23 pages, 8069 KiB  
Article
The Role of –OEt Substituents in Molybdenum-Assisted Pentathiepine Formation—Access to Diversely Functionalized Azines
by Roberto Tallarita, Lukas M. Jacobsen, Siva S. M. Bandaru, Benedict J. Elvers and Carola Schulzke
Molecules 2024, 29(16), 3806; https://doi.org/10.3390/molecules29163806 - 11 Aug 2024
Viewed by 570
Abstract
1,2,3,4,5-pentathiepines (PTEs) are naturally occurring polysulfides of increasing scientific interest based on their identified pharmacological activities. Artificial PTEs with N-heterocyclic backbones are efficiently synthesized via mediation by a molybdenum–oxo-bistetrasulfido complex. A common feature of all precursor alkynes successfully used to date in [...] Read more.
1,2,3,4,5-pentathiepines (PTEs) are naturally occurring polysulfides of increasing scientific interest based on their identified pharmacological activities. Artificial PTEs with N-heterocyclic backbones are efficiently synthesized via mediation by a molybdenum–oxo-bistetrasulfido complex. A common feature of all precursor alkynes successfully used to date in this reaction is the presence of a –CH(OEt)2 group since the previously postulated mechanism requires the presence of one OEt as the leaving group, and the second must become a transient ethoxonium moiety. This raised the question of whether there really is a need for two, maybe only one, or possibly even zero ethoxy substituents. This research problem was systematically addressed by respective variations in the precursor-alkyne derivatives and by employing one related allene species. It was found that the total absence of ethoxy substituents prevents the formation of PTEs entirely, while the presence of a single ethoxy group results in the possibility to distinctly functionalize the position on the resulting N-heterocyclic pyrrole five ring in the target compound. This position was previously exclusively occupied by an –OEt for all products of the molybdenum-mediated reaction. The allene was applied with similar success as precursor as with the related alkyne. The now-employable significant change in precursor composition gives access to a whole new PTE subfamily, allowing further modulation of (physico)-chemical properties such as solubility, and provides additional insight into the mechanism of PTE formation; it comprises a merely partial validation of the previous hypothesis. The new alkyne precursors and pentathiepines were characterized by a variety of instrumental analyses (NMR, mass spec, UV–vis) and in six cases (one alkyne precursor, one unexpected side product, and four PTEs) by single-crystal X-ray diffraction. Syntheses, isolation procedures, analytical data, and the impact of the findings on the previously proposed mechanism are described in detail herein. Full article
(This article belongs to the Special Issue Cyclization Reactions in Organic Synthesis: Recent Developments)
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20 pages, 2678 KiB  
Article
Nickel(II)-Catalyzed Formal [3+2] Cycloadditions between Indoles and Donor–Acceptor Cyclopropanes
by Víctor Quezada, Mariña Castroagudín, Felipe Verdugo, Sergio Ortiz, Guillermo Zaragoza, Fabiane M. Nachtigall, Francisco A. A. Reis, Alejandro Castro-Alvarez, Leonardo S. Santos and Ronald Nelson
Molecules 2024, 29(7), 1604; https://doi.org/10.3390/molecules29071604 - 3 Apr 2024
Viewed by 1122
Abstract
This article describes the development of a nickel-catalyzed regio- and diastereoselective formal [3+2] cycloaddition between N-substituted indoles and donor–acceptor cyclopropanes to synthesize cyclopenta[b]indoles. Optimized reaction conditions provide the desired nitrogen-containing cycloadducts in up to 93% yield and dr 8.6:1 with [...] Read more.
This article describes the development of a nickel-catalyzed regio- and diastereoselective formal [3+2] cycloaddition between N-substituted indoles and donor–acceptor cyclopropanes to synthesize cyclopenta[b]indoles. Optimized reaction conditions provide the desired nitrogen-containing cycloadducts in up to 93% yield and dr 8.6:1 with complete regioselectivity. The substrate scope showed high tolerance to various substituted indoles and cyclopropanes, resulting in the synthesis of six new cyclopenta[b]indoles and the isolation of five derivatives previously reported in the literature. In addition, a mechanistic proposal for the reaction was studied through online reaction monitoring by ESI-MS, allowing for the identification of the reactive intermediates in the Ni(II) catalyzed process. X-ray crystallography confirmed the structure and relative endo stereochemistry of the products. This method enables the fast and efficient construction of fused indolines from readily accessible starting materials. Full article
(This article belongs to the Special Issue Cyclization Reactions in Organic Synthesis: Recent Developments)
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16 pages, 2928 KiB  
Article
Persulfate-Promoted Carbamoylation/Cyclization of Alkenes: Synthesis of Amide-Containing Quinazolinones
by Jia-Jun Tang, Meng-Yang Zhao, Ying-Jun Lin, Li-Hua Yang and Long-Yong Xie
Molecules 2024, 29(5), 997; https://doi.org/10.3390/molecules29050997 - 25 Feb 2024
Viewed by 905
Abstract
The incorporation of amide groups into biologically active molecules has been proven to be an efficient strategy for drug design and discovery. In this study, we present a simple and practical method for the synthesis of amide-containing quinazolin-4(3H)-ones under transition-metal-free conditions. [...] Read more.
The incorporation of amide groups into biologically active molecules has been proven to be an efficient strategy for drug design and discovery. In this study, we present a simple and practical method for the synthesis of amide-containing quinazolin-4(3H)-ones under transition-metal-free conditions. This is achieved through a carbamoyl-radical-triggered cascade cyclization of N3-alkenyl-tethered quinazolinones. Notably, the carbamoyl radical is generated in situ from the oxidative decarboxylative process of oxamic acids in the presence of (NH4)2S2O8. Full article
(This article belongs to the Special Issue Cyclization Reactions in Organic Synthesis: Recent Developments)
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Review

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57 pages, 18372 KiB  
Review
Radical Cyclization-Initiated Difunctionalization Reactions of Alkenes and Alkynes
by Sanjun Zhi, Xiaoming Ma and Wei Zhang
Molecules 2024, 29(11), 2559; https://doi.org/10.3390/molecules29112559 - 29 May 2024
Cited by 1 | Viewed by 949
Abstract
Radical reactions are powerful in the synthesis of diverse molecular scaffolds bearing functional groups. In previous review articles, we have presented 1,2-difunctionalizations, remote 1,3-, 1,4-, 1,5-, 1,6- and 1,7-difunctionalizations, and addition followed by cyclization reactions. Presented in this paper is radical cyclization followed [...] Read more.
Radical reactions are powerful in the synthesis of diverse molecular scaffolds bearing functional groups. In previous review articles, we have presented 1,2-difunctionalizations, remote 1,3-, 1,4-, 1,5-, 1,6- and 1,7-difunctionalizations, and addition followed by cyclization reactions. Presented in this paper is radical cyclization followed by the second functionalization reaction. The second functionalization could be realized by atom transfer reactions, radical or transition metal-assisted coupling reactions, and reactions with neutral molecules, cationic and anionic species. Full article
(This article belongs to the Special Issue Cyclization Reactions in Organic Synthesis: Recent Developments)
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