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45 pages, 5593 KB

Open AccessReview

Synthesis of 2-Oxazolines from N-Allyl and N-Propargyl Amides

by Karolina Bojar, Danuta Branowska and Ewa Wolińska

Molecules 2025, 30(22), 4369; https://doi.org/10.3390/molecules30224369 - 12 Nov 2025

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2-Oxazolines are five-membered heterocyclic compounds with significant biological properties. They also play an important role in organic synthesis, acting as chiral ligands and protecting groups for hydroxyamino acids and amino alcohols. Poly(2-oxazolines) are known coating materials, for example, in biomedicine. Classic synthetic methods [...] Read more.

2-Oxazolines are five-membered heterocyclic compounds with significant biological properties. They also play an important role in organic synthesis, acting as chiral ligands and protecting groups for hydroxyamino acids and amino alcohols. Poly(2-oxazolines) are known coating materials, for example, in biomedicine. Classic synthetic methods of 2-oxazolines involve a dehydrative cyclisation reaction between amino alcohols and carboxylic acids, acid chlorides, nitriles, imidates, and aldehydes. However, the electrophilic intramolecular cyclization of unsaturated amides is becoming an increasingly important synthetic method for the preparation of 2-oxazolines. This brief review summarizes procedures for synthesizing oxazolines using the electrophilic intramolecular oxidative cyclisation of N-allyl and N-propargyl amides, as published between 2014 and 2024. It covers the synthesis of 5-halomethyl-, 5-trifluoromethyl-, 5-sulfonylmethyl-, 5-sulfenylmethyl-, 5-selenylmethyl-, 5-acetoxymethyl-, 5-hydroxymethyl-, 5-aminomethyl-, 5-alkilo-, and 5-alkylideneoxazolines. Full article

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25 pages, 6231 KB

Open AccessReview

1,3-Dipolar Cycloaddition of Nitrile Imines and Nitrile Oxides to Exocyclic C=N Bonds—An Approach to Spiro-N-Heterocycles

by Juliana V. Petrova, Maxim E. Kukushkin and Elena K. Beloglazkina

Int. J. Mol. Sci. 2025, 26(17), 8673; https://doi.org/10.3390/ijms26178673 - 5 Sep 2025

Viewed by 1716

Abstract

Nitrile imines and nitrile oxides are capable of undergoing (3+2)-cycloaddition reactions at double and triple carbon–carbon, carbon-heteroatom, or heteroatom–heteroatom bonds of various dipolarophiles, forming five-membered heterocyclic compounds. When cyclic dipolarophiles bearing an exocyclic carbon–nitrogen double bond (exo-C=N) are introduced into the reaction with [...] Read more.

Nitrile imines and nitrile oxides are capable of undergoing (3+2)-cycloaddition reactions at double and triple carbon–carbon, carbon-heteroatom, or heteroatom–heteroatom bonds of various dipolarophiles, forming five-membered heterocyclic compounds. When cyclic dipolarophiles bearing an exocyclic carbon–nitrogen double bond (exo-C=N) are introduced into the reaction with these dipoles, spiro-fused 1,2,4-triazoline or 1,2,4-oxadiazoline cycles are formed. Such reactions can provide efficient synthetic approaches to spiro-heterocyclic compounds with enhanced biological activity. This review comprehensively summarizes the literature data on the 1,3-dipolar cycloaddition of nitrile imines and nitrile oxides to exo-C=N bonds for spiro compound synthesis. The research area covers reactions of both saturated and unsaturated dipolarophiles, monocyclic and polycyclic molecules, as well as compounds containing one to three heteroatoms, with special emphasis on systems containing biologically significant heterocyclic pharmacophores. Recent advances in reaction techniques, such as microwave and ultrasonic activation, as well as one-pot and diffusion protocols, are also mentioned. Full article

(This article belongs to the Section Biochemistry)

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30 pages, 6753 KB

Open AccessArticle

Regioselective Synthesis of 5-Substituted 3-(β-d-Glycopyranosyl)isoxazoles and -isoxazolines by 1,3-Dipolar Cycloaddition as Potential Anticancer Agents and Glycogen Phosphorylase Inhibitors

by Tímea Kaszás, Bence Szakács, Márta Bertalan, Tekla Blága, Faria Hameed, Ákos Lengyel, Samreen Saifi, Éva Juhász-Tóth, Luca A. Varga, Tibor Docsa, Adrienn Sipos, Péter Bai, Anita Ábrahám, Attila Kiss-Szikszai, Sándor Kun, György Attila Kiss, János József, László Juhász and Marietta Tóth

Int. J. Mol. Sci. 2025, 26(17), 8167; https://doi.org/10.3390/ijms26178167 - 22 Aug 2025

Viewed by 1179

Abstract

Anhydro-aldose oximes were employed to generate in situ nitrile oxides via a halogenation/base-induced elimination sequence in the presence of NCS and Et₃N, which were then used in 1,3-dipolar cycloadditions with alkenes and alkynes to afford 5-substituted 3-(β-d-glycopyranosyl)isoxazole and -isoxazoline [...] Read more.

Anhydro-aldose oximes were employed to generate in situ nitrile oxides via a halogenation/base-induced elimination sequence in the presence of NCS and Et₃N, which were then used in 1,3-dipolar cycloadditions with alkenes and alkynes to afford 5-substituted 3-(β-d-glycopyranosyl)isoxazole and -isoxazoline derivatives exclusively. These newly synthesized glycomimetics were evaluated for their potential to act as antagonists of A2780 ovarian cancer cells and as inhibitors of glycogen phosphorylase; however, they exhibited no significant activity. Full article

(This article belongs to the Section Molecular Biology)

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15 pages, 2212 KB

Open AccessArticle

A Study on the Aging Mechanism and Anti-Aging Properties of Nitrile Butadiene Rubber: Experimental Characterization and Molecular Simulation

by Min Zhu, Hanyuan Huang, Haiyan Li, Gui Huang, Jingjing Lan, Jing Fu, Juqin Fan, Yujun Liu, Zhiwu Ke, Xiaojie Guo, Hongkuan Zhou and Yan Li

Polymers 2025, 17(11), 1446; https://doi.org/10.3390/polym17111446 - 23 May 2025

Cited by 3 | Viewed by 1863

Abstract

To tackle the degradation of sealing performance in nitrile butadiene rubber (NBR) seals due to material aging during long-term service, this study integrates experimental and molecular simulation methods to elucidate the aging mechanism. Experimental results reveal that the contents of C=C and C=O [...] Read more.

To tackle the degradation of sealing performance in nitrile butadiene rubber (NBR) seals due to material aging during long-term service, this study integrates experimental and molecular simulation methods to elucidate the aging mechanism. Experimental results reveal that the contents of C=C and C=O functional groups significantly decrease during aging, accompanied by enhanced hydrophobicity and increased crosslink density of NBR, indicating that crosslinking reactions dominate the aging process with the participation of C=C and C=O groups. Quantum mechanics (QM) and molecular dynamics (MD) simulations further demonstrate that α-H, C=C, and C≡N groups are preferentially oxidized due to their low bond energies. The oxidation of NBR generates unstable epoxy intermediates, which undergo chain scission to form ketones, aldehydes, and ultimately crosslinked structures. Using a multi-dimensional evaluation system based on bond dissociation energy (BDE), solubility parameter (Δδ), and migration coefficient (MSD), four antioxidants (4010NA, 4010, MC, and BHT) were screened. BHT emerges as the optimal choice, exhibiting superior free radical scavenging ability (BDE = 346.3 kJ/mol), good matrix compatibility (Δδ = 2.95), and anti-migration properties. The MD-based screening method established herein provides a theoretical basis for designing antioxidant systems in high-performance rubber materials, facilitating the development of advanced rubber products. Full article

(This article belongs to the Special Issue Exploration and Innovation in Sustainable Rubber Performance)

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25 pages, 5183 KB

Open AccessArticle

A Comprehensive Study of the Synthesis, Spectral Characteristics, Quantum–Chemical Molecular Electron Density Theory, and In Silico Future Perspective of Novel CBr₃-Functionalyzed Nitro-2-Isoxazolines Obtained via (3 + 2) Cycloaddition of (E)-3,3,3-Tribromo-1-Nitroprop-1-ene

by Karolina Zawadzińska-Wrochniak, Karolina Kula, Mar Ríos-Gutiérrez, Bartłomiej Gostyński, Tomasz Krawczyk and Radomir Jasiński

Molecules 2025, 30(10), 2149; https://doi.org/10.3390/molecules30102149 - 13 May 2025

Cited by 3 | Viewed by 1546

Abstract

The search for new heterocyclic compounds with biological potential is one of the current challenges in modern chemistry. Therefore, the comprehensive study of (3 + 2) cycloaddition (32CA) reactions between a series of aryl-substituted nitrile N-oxides (NOs) and (E)-3,3,3-tribromo-1-nitroprop-1-ene (TBNP) is [...] Read more.

The search for new heterocyclic compounds with biological potential is one of the current challenges in modern chemistry. Therefore, the comprehensive study of (3 + 2) cycloaddition (32CA) reactions between a series of aryl-substituted nitrile N-oxides (NOs) and (E)-3,3,3-tribromo-1-nitroprop-1-ene (TBNP) is carried out. According to the experimental research, in all tested 32CAs, the proper (4RS,5RS)-3-aryl-4-nitro-5-tribromomethyl-2-isoxazolines are obtained as only one reaction product. In turn, the quantum–chemical MEDT study shows that the creation of heterocycles occur via the polar attack of zwitterionic moderate-nucleophilic NOs to strong electrophilic TBNP. The reactions are realized according to a two-stage, one-step asynchronous mechanism, in which the formation of the O-C(CBr₃) bond takes place once the C-C(NO₂) bond is already formed. What is more, the computational analysis confirmed the experimental results. At the end, the obtained 2-isoxazolines were docked to three proteins: gelatinase B, cyclooxygenase COX-1, and Caspase-7. We hope that the presented study will be helpful for searching for the future direction of application for this class of organic compounds. Full article

(This article belongs to the Special Issue Methods and Applications of Cycloaddition Reactions)

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12 pages, 2310 KB

Open AccessArticle

[3+2] Cycloaddition to a Chiral 5-Methylene-1,3-dioxolan-4-one and Pyrolysis of the Spiro Adducts

by R. Alan Aitken, Lynn A. Power and Alexandra M. Z. Slawin

Molecules 2025, 30(6), 1246; https://doi.org/10.3390/molecules30061246 - 10 Mar 2025

Viewed by 1055

Abstract

The [3+2] cycloaddition chemistry of (2S)-5-methylene-2-t-butyl-1,3-dioxolan-4-one, derived from lactic acid, has been examined, and spiro adducts have been obtained with benzonitrile oxide, acetonitrile oxide, diazomethane and diphenyldiazomethane. The structure and absolute stereochemistry of the benzonitrile oxide adduct has been [...] Read more.

The [3+2] cycloaddition chemistry of (2S)-5-methylene-2-t-butyl-1,3-dioxolan-4-one, derived from lactic acid, has been examined, and spiro adducts have been obtained with benzonitrile oxide, acetonitrile oxide, diazomethane and diphenyldiazomethane. The structure and absolute stereochemistry of the benzonitrile oxide adduct has been confirmed by X-ray diffraction, and all the adducts have been fully characterised by ¹H and ¹³C NMR. Attempted cycloaddition with a nitrile sulfide, a nitrile imine and azides failed. Pyrolysis results in a range of novel gas-phase reactions, with the nitrile oxide adducts giving pivalaldehyde, CO₂, the nitrile and ketene, the diazomethane adduct losing only N₂ to give a cyclopropane-fused dioxolanone, and the diphenylcyclopropane derived from diphenyldiazomethane giving mainly benzophenone in a sequence involving the loss of pivalaldehyde and methyleneketene. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates—Second Edition)

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17 pages, 5267 KB

Open AccessArticle

The Puzzle of the Regioselectivity and Molecular Mechanism of the (3+2) Cycloaddition Reaction Between E-2-(Trimethylsilyl)-1-Nitroethene and Arylonitrile N-Oxides: Molecular Electron Density Theory (MEDT) Quantumchemical Study

by Mikołaj Sadowski, Ewa Dresler and Radomir Jasiński

Molecules 2025, 30(4), 974; https://doi.org/10.3390/molecules30040974 - 19 Feb 2025

Cited by 3 | Viewed by 1431

Abstract

The regioselectivity and molecular mechanism of the (3+2) cycloaddition reaction between E-2-(trimethylsilyl)-1-nitroethene and arylonitrile N-oxides were explored on the basis of the ωB97XD/6-311+G(d) (PCM) quantumchemical calculations. It was found that the earlier postulate regarding the regioselectivity of the cycloaddition stage should [...] Read more.

The regioselectivity and molecular mechanism of the (3+2) cycloaddition reaction between E-2-(trimethylsilyl)-1-nitroethene and arylonitrile N-oxides were explored on the basis of the ωB97XD/6-311+G(d) (PCM) quantumchemical calculations. It was found that the earlier postulate regarding the regioselectivity of the cycloaddition stage should be undermined. Within our research, several aspects of the title reaction were also examined: interactions between reagents, electronic structures of alkenes and nitrile oxides, the nature of transition states, the influence of the polarity solvent on the reaction selectivity and mechanism, substituent effects, etc. The obtained results offer a general conclusion for all of the important aspects of some groups of cycloaddition processes. Full article

(This article belongs to the Special Issue Quantum Chemical Calculations of Molecular Reaction Processes)

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25 pages, 2653 KB

Open AccessArticle

1,3-Dipolar Cycloaddition of Nitrile Oxides and Nitrilimines to (−)-β-Caryophyllene: Stereoselective Synthesis of Polycyclic Derivatives and Their Biological Testing

by Dmitry E. Shybanov, Maxim E. Kukushkin, Yuri K. Grishin, Vitaly A. Roznyatovsky, Viktor A. Tafeenko, Louay Abo Qoura, Vadim S. Pokrovsky, Olga I. Yarovaya, Svetlana V. Belyaevskaya, Alexandrina S. Volobueva, Iana L. Esaulkova, Vladimir V. Zarubaev and Elena K. Beloglazkina

Int. J. Mol. Sci. 2024, 25(21), 11435; https://doi.org/10.3390/ijms252111435 - 24 Oct 2024

Cited by 5 | Viewed by 3581

Abstract

The cycloaddition of nitrile oxides and nitrilimines to one or both of the C=C double bonds of caryophyllene is described. The possibility of introducing five-membered fused and spiro-linked heterocycles into the structure of sesquiterpenes by the 1,3-dipolar cycloaddition reactions of nitrile oxides and [...] Read more.

The cycloaddition of nitrile oxides and nitrilimines to one or both of the C=C double bonds of caryophyllene is described. The possibility of introducing five-membered fused and spiro-linked heterocycles into the structure of sesquiterpenes by the 1,3-dipolar cycloaddition reactions of nitrile oxides and nitrilimines to caryophyllene was demonstrated. As a result of these reactions, pharmacophore fragments of isoxazoline and pyrazoline are introduced into the structure of caryophyllene, which leads to an increase in the conformational rigidity of the molecule. A complete stereochemical assignment of 1,3-dipolar cycloaddition adducts to caryophyllene was carried out. The study of antiviral and cytotoxic activity for some heterocyclic derivatives synthesized in this work revealed relatively high biological activity of previously little-studied cycloaddition adducts at the exocyclic C=CH₂ bond of caryophyllene. The effect of substituents in the synthesized heterocycles on biological activity was demonstrated. Compounds with a good inhibitory effect on the H1N1 influenza virus were revealed. The activity of the compound was demonstrated up to 6 h post infection, and this could be due to slight inhibiting activity against viral neuraminidase, necessary at the stage of progeny virion budding. Full article

(This article belongs to the Special Issue Design, Synthesis and Biological Applications of Functional Compounds and Materials)

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13 pages, 2237 KB

Open AccessArticle

Research on Synthesis, Structure, and Catalytic Performance of Tetranuclear Copper(I) Clusters Supported by 2-Mercaptobenz-zole-Type Ligands

by Tingyu Zhu, Wangyuan Zhan, Weibin Fan and Xiaofeng Zhang

Molecules 2024, 29(17), 4228; https://doi.org/10.3390/molecules29174228 - 6 Sep 2024

Viewed by 2184

Abstract

Tetrahedral copper(I) clusters [Cu₄(MBIZ)₄(PPh₃)₂] (2), [Cu₄(MBOZ)₄(PPh₃)₄] (6) (MBIZ = 2-mercaptobenzimidazole, MBOZ = 2-mercaptobenzoxazole) were prepared by regulation of the copper-thiolate clusters [Cu₆ [...] Read more.

Tetrahedral copper(I) clusters [Cu₄(MBIZ)₄(PPh₃)₂] (2), [Cu₄(MBOZ)₄(PPh₃)₄] (6) (MBIZ = 2-mercaptobenzimidazole, MBOZ = 2-mercaptobenzoxazole) were prepared by regulation of the copper-thiolate clusters [Cu₆(MBIZ)₆] (1) and [Cu₈(MBOZ)₈I]⁻ (5) with PPh₃. With the presence of iodide anion, the regulation provided the iodide-containing clusters [Cu^I₄(MBIZ)₃(PPh₃)₃I] (3) and [Cu^I₄(MBOZ)₃(PPh₃)₃I] (7). The cyclic voltammogram of 3 in MeCN (0.1 M ⁿBu₄NPF₆, 298 K) at a scan rate of 100 mV s⁻¹ shows two oxidation processes at E_p^a = +0.11 and +0.45 V with return waves observed at E_p^c = +0.25 V (vs. Fc⁺/Fc). Complex 3 has a higher capability to lose and gain electrons in the redox processes than complexes 2, 4, 4′, 6, and 7. Its thermal stability was confirmed by thermogravimetric analysis. The catalytic performance of 3 was demonstrated by the catalytic transformation of iodobenzenes to benzonitriles using AIBN as the cyanide source. The nitrile products show potential applications in the preparation of 1,3,5-triazine compounds for organic fluorescence materials. Full article

(This article belongs to the Section Inorganic Chemistry)

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15 pages, 3065 KB

Open AccessEditor’s ChoiceArticle

Energetic Aspects and Molecular Mechanism of 3-Nitro-substituted 2-Isoxazolines Formation via Nitrile N-Oxide [3+2] Cycloaddition: An MEDT Computational Study

by Ewa Dresler, Aneta Wróblewska and Radomir Jasiński

Molecules 2024, 29(13), 3042; https://doi.org/10.3390/molecules29133042 - 26 Jun 2024

Cited by 19 | Viewed by 4126

Abstract

Regioselectivity and the molecular mechanism of the [3+2] cycloaddition reaction between nitro-substituted formonitrile N-oxide 1 and electron-rich alkenes were explored on the basis of the wb97xd/6-311+G(d) (PCM) quantum chemical calculations. It was established that the thermodynamic factors allow for the formation of stable [...] Read more.

Regioselectivity and the molecular mechanism of the [3+2] cycloaddition reaction between nitro-substituted formonitrile N-oxide 1 and electron-rich alkenes were explored on the basis of the wb97xd/6-311+G(d) (PCM) quantum chemical calculations. It was established that the thermodynamic factors allow for the formation of stable cycloadducts along all considered models. The analysis of the kinetic parameters of the main processes show that all [3+2] cycloadditions should be realized with full regioselectivity. In all cases, the formation of 5-substituted 3-nitro-2-isoxazolidines is clearly preferred. It is interesting that regiodirection is not determined by the local electrophile/nucleophile interactions but by steric effects. From a mechanistic point of view, all considered reactions should be treated as polar, one-step reactions. All attempts to locate the hypothetical zwitterionic intermediates along the cycloaddition paths were, however, not successful. Full article

(This article belongs to the Special Issue Advances in the Synthesis of Heterocyclic Compounds and Their Applications)

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18 pages, 3448 KB

Open AccessArticle

Spectral Assignment in the [3 + 2] Cycloadditions of Methyl (2E)-3-(Acridin-4-yl)-prop-2-enoate and 4-[(E)-2-Phenylethenyl]acridin with Unstable Nitrile N-Oxides

by Lucia Ungvarská Maľučká and Mária Vilková

Molecules 2024, 29(12), 2756; https://doi.org/10.3390/molecules29122756 - 9 Jun 2024

Cited by 2 | Viewed by 1674

Abstract

The investigation of cycloaddition reactions involving acridine-based dipolarophiles revealed distinct regioselectivity patterns influenced mainly by the electronic factor. Specifically, the reactions of methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate and 4-[(1E)-2-phenylethenyl]acridine with unstable benzonitrile N-oxides were studied. For methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate, the formation of two [...] Read more.

The investigation of cycloaddition reactions involving acridine-based dipolarophiles revealed distinct regioselectivity patterns influenced mainly by the electronic factor. Specifically, the reactions of methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate and 4-[(1E)-2-phenylethenyl]acridine with unstable benzonitrile N-oxides were studied. For methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate, the formation of two regioisomers favoured the 5-(acridin-4-yl)-4,5-dihydro-1,2-oxazole-4-carboxylates, with remarkable exclusivity in the case of 4-methoxybenzonitrile oxide. Conversely, 4-[(1E)-2-phenylethenyl]acridine displayed reversed regioselectivity, favouring products 4-[3-(substituted phenyl)-5-phenyl-4,5-dihydro-1,2-oxazol-4-yl]acridine. Subsequent hydrolysis of isolated methyl 5-(acridin-4-yl)-3-phenyl-4,5-dihydro-1,2-oxazole-4-carboxylates resulted in the production of carboxylic acids, with nearly complete conversion. During NMR measurements of carboxylic acids in CDCl₃, decarboxylation was observed, indicating the formation of a new prochiral carbon centre C-4, further confirmed by a noticeable colour change. Overall, this investigation provides valuable insights into regioselectivity in cycloaddition reactions and subsequent transformations, suggesting potential applications across diverse scientific domains. Full article

(This article belongs to the Special Issue New Insights into Nuclear Magnetic Resonance (NMR) Spectroscopy)

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24 pages, 3618 KB

Open AccessArticle

Acridine–Isoxazole and Acridine–Azirine Hybrids: Synthesis, Photochemical Transformations in the UV/Visible Radiation Boundary Region, and Anticancer Activity

by Ekaterina E. Galenko, Mikhail S. Novikov, Alexander S. Bunev and Alexander F. Khlebnikov

Molecules 2024, 29(7), 1538; https://doi.org/10.3390/molecules29071538 - 29 Mar 2024

Cited by 5 | Viewed by 2197

Abstract

Easy-to-handle N-hydroxyacridinecarbimidoyl chloride hydrochlorides were synthesized as convenient nitrile oxide precursors in the preparation of 3-(acridin-9/2-yl)isoxazole derivatives via 1,3-dipolar cycloaddition with terminal alkynes, 1,1-dichloroethene, and acrylonitrile. Azirines with an acridin-9/2-yl substituent attached directly or via the 1,2,3-triazole linker to the azirine C2 [...] Read more.

Easy-to-handle N-hydroxyacridinecarbimidoyl chloride hydrochlorides were synthesized as convenient nitrile oxide precursors in the preparation of 3-(acridin-9/2-yl)isoxazole derivatives via 1,3-dipolar cycloaddition with terminal alkynes, 1,1-dichloroethene, and acrylonitrile. Azirines with an acridin-9/2-yl substituent attached directly or via the 1,2,3-triazole linker to the azirine C2 were also synthesized. The three-membered rings of the acridine–azirine hybrids were found to be resistant to irradiation in the UV/visible boundary region, despite their long-wave absorption at 320–420 nm, indicating that the acridine moiety cannot be used as an antenna to transfer light energy to generate nitrile ylides from azirines for photoclick cycloaddition. The acridine–isoxazole hybrids linked at the C9–C3 or C2–C3 atoms under blue light irradiation underwent the addition of such hydrogen donor solvents, such as, toluene, o-xylene, mesitylene, 4-chlorotoluene, THF, 1,4-dioxane, or methyl tert-butyl ether (MTBE), to the acridine system to give the corresponding 9-substituted acridanes in good yields. The synthesized acridine–azirine, acridine–isoxazole, and acridane–isoxazole hybrids exhibited cytotoxicity toward both all tested cancer cell lines (HCT 116, MCF7, and A704) and normal cells (WI-26 VA4). Full article

(This article belongs to the Section Organic Chemistry)

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16 pages, 2692 KB

Open AccessArticle

tert-Butyl Nitrite-Induced Radical Nitrile Oxidation Cycloaddition: Synthesis of Isoxazole/Isoxazoline-Fused Benzo 6/7/8-membered Oxacyclic Ketones

by Jian-Kang Cao, Tian-Zheng Cao, Qian-Wen Yue, Ying Ma, Chuan-Ming Yang, Hong-Xi Zhang, Ya-Chen Li, Qiao-Ke Dong, Yan-Ping Zhu and Yuan-Yuan Sun

Molecules 2024, 29(6), 1202; https://doi.org/10.3390/molecules29061202 - 7 Mar 2024

Cited by 1 | Viewed by 3025

Abstract

A practical metal-free and additive-free approach for the synthesis of 6/7/8-membered oxacyclic ketone-fused isoxazoles/isoxazolines tetracyclic or tricyclic structures is reported through C_sp³–H bond radical nitrile oxidation and the intramolecular cycloaddition of alkenyl/alkynyl-substituted aryl methyl ketones. This convenient approach enables the [...] Read more.

A practical metal-free and additive-free approach for the synthesis of 6/7/8-membered oxacyclic ketone-fused isoxazoles/isoxazolines tetracyclic or tricyclic structures is reported through C_sp³–H bond radical nitrile oxidation and the intramolecular cycloaddition of alkenyl/alkynyl-substituted aryl methyl ketones. This convenient approach enables the simultaneous formation of isoxazole/isoxazoline and 6/7/8-membered oxacyclic ketones to form polycyclic architectures by using tert-butyl nitrite (TBN) as a non-metallic radical initiator and N–O fragment donor. Full article

(This article belongs to the Special Issue Metal-Catalyzed Organic Transformations: Expanding Horizons in Synthetic Methodology)

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5 pages, 887 KB

Open AccessCommunication

Synthesis of a Novel Tetracyclic Isoxazole by Intramolecular Nitrile Oxide Cycloaddition

by Gavin R. Hoffman and Allen M. Schoffstall

Molbank 2024, 2024(1), M1767; https://doi.org/10.3390/M1767 - 1 Feb 2024

Cited by 3 | Viewed by 3882

Abstract

Intramolecular cycloadditions have the great advantage of forming two rings simultaneously. We report the use of intramolecular [3 + 2] cycloaddition of the nitrile oxide derived from an N-propargylbenzimidazole oxime in the synthesis of a hitherto unreported tetracyclic isoxazole-containing ring system bearing [...] Read more.

Intramolecular cycloadditions have the great advantage of forming two rings simultaneously. We report the use of intramolecular [3 + 2] cycloaddition of the nitrile oxide derived from an N-propargylbenzimidazole oxime in the synthesis of a hitherto unreported tetracyclic isoxazole-containing ring system bearing “6-5-5-5”-membered ring fusions. The initial condensation was achieved through reaction of o-phenylenediamine with ethyl diethoxyacetate, followed by alkylation with propargyl bromide, deprotection of the acetal to the aldehyde, formation of an aldoxime, and intramolecular nitrile oxide cycloaddition (INOC). Characterization of the aldoxime and tetracyclic isoxazole is included herein. Full article

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23 pages, 1568 KB

Open AccessArticle

Naphtho[1,8-de][1,2]Oxazin-4-ol: Precursor to 1,2,8-Trisubstituted Naphthalenes and 1-Unsubstituted Naphtho[1,2-d]isoxazole 2-Oxide: A Novel Isomerization of the N-Oxide to Nitrile Oxide en Route to Isoxazol(in)es

by Ioannis E. Gerontitis, Petros G. Tsoungas and George Varvounis

Molecules 2024, 29(1), 48; https://doi.org/10.3390/molecules29010048 - 20 Dec 2023

Cited by 1 | Viewed by 2651

Abstract

Naphtho[1,8-de][1,2]oxazin-4-ol and its acyl or benzyl derivatives ring open to various 2,8-dihydroxy-1-naphthonitriles, which, through (de)protection protocols and reduction, afford the target (E)-2-hydroxy-8-methoxy-1-naphthaldehyde. This was converted to its corresponding oxime, which was oxidatively o-cyclized with phenyliodine(III) diacetate (PIDA) to [...] Read more.

Naphtho[1,8-de][1,2]oxazin-4-ol and its acyl or benzyl derivatives ring open to various 2,8-dihydroxy-1-naphthonitriles, which, through (de)protection protocols and reduction, afford the target (E)-2-hydroxy-8-methoxy-1-naphthaldehyde. This was converted to its corresponding oxime, which was oxidatively o-cyclized with phenyliodine(III) diacetate (PIDA) to 9-methoxynaphtho[1,2-d]isoxazole 2-oxide. The latter, in deuterated DMSO at room temperature, was rearranged to its isomer 2-hydroxy-8-methoxy(naphthalen-1-yl)nitrile oxide. The isomerization was detected by time-course plot ¹H NMR spectroscopy and further identified from its ¹³C NMR and HRMS spectra. The nitrile oxide was stable in (non)deuterated DMSO for at least 18 h. A 3,4-bis(2-hydroxy-8-methoxynaphthalen-1-yl)-1,2,5-oxadiazole 2-oxide, as a dimerization product or an isocyanate as a rearrangement isomer, was ruled out, the former by its HRMS spectrum and the latter by its 1,3-dipolar cycloaddition reactions to substituted isoxazoles. Full article

(This article belongs to the Section Organic Chemistry)

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