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14 pages, 5297 KB

Open AccessFeature PaperArticle

Metal-Free Photoredox Intramolecular Cyclization of N-Aryl Acrylamides

by Zhaosheng Liu, Xiaochen Ji, Feng Zhao, Guojun Deng and Huawen Huang

Catalysts 2023, 13(6), 1007; https://doi.org/10.3390/catal13061007 - 14 Jun 2023

Cited by 2 | Viewed by 2842

A novel metal-free photoredox-catalyzed cyclization reaction of N-aryl acrylamide is herein reported that provides synthetically valuable oxindole derivatives through the bis-mediation of H₂O and aldehyde. In this work, sustainable visible light was used as the energy source, and the organic [...] Read more.

A novel metal-free photoredox-catalyzed cyclization reaction of N-aryl acrylamide is herein reported that provides synthetically valuable oxindole derivatives through the bis-mediation of H₂O and aldehyde. In this work, sustainable visible light was used as the energy source, and the organic light-emitting molecule 4CzIPN served as the efficient photocatalyst. The main characteristics of this reaction are environmentally friendly and high yields. Full article

(This article belongs to the Special Issue Radical-Mediated Functionalization of Alkenes)

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14 pages, 2441 KB

Open AccessFeature PaperArticle

Gold(I)-Catalyzed Direct Alkyne Hydroarylation in Ionic Liquids: Mechanistic Insights

by Sara Bonfante, Pietro Bax, Marco Baron and Andrea Biffis

Catalysts 2023, 13(5), 822; https://doi.org/10.3390/catal13050822 - 29 Apr 2023

Cited by 3 | Viewed by 2050

Abstract

The factors determining the catalytic performance of a recently discovered system for direct intermolecular alkyne hydroarylations, comprising a gold(I) complex of general formula LAuX (L = neutral ligand; X = weakly coordinating counteranion) and an ionic liquid as solvent, have been investigated. In [...] Read more.

The factors determining the catalytic performance of a recently discovered system for direct intermolecular alkyne hydroarylations, comprising a gold(I) complex of general formula LAuX (L = neutral ligand; X = weakly coordinating counteranion) and an ionic liquid as solvent, have been investigated. In particular, the effect of the ionic liquid anion, cation, and of the electronic and steric properties of the neutral ligand L have been considered. The results of the investigation shed some light in particular on the role of the anion, which is multiform and can potentially influence the catalytic performance in many respects, and on the role of the neutral ligand, which should be a relatively poor electron donor but not so much as to compromise the stability of the catalyst. Knowledge of the factors affecting catalytic performance will speed up the optimization of this catalytic system, in the case of direct alkyne hydroarylations with different substrates, and will also facilitate the extension of its application to other reactions. Full article

(This article belongs to the Collection Gold Catalysts)

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27 pages, 7657 KB

Open AccessReview

Asymmetric Hydroarylation Reactions Catalyzed by Transition Metals: Last 10 Years in a Mini Review

by Martina De Angelis, Antonia Iazzetti, Andrea Serraiocco and Alessia Ciogli

Catalysts 2022, 12(10), 1289; https://doi.org/10.3390/catal12101289 - 21 Oct 2022

Cited by 11 | Viewed by 3650

Abstract

Hydroarylation reactions play a pivotal role in organic chemistry due to their versatility and efficiency. In the last 10 years, the scientific production around this reaction has been very high, but in its asymmetric version, the results are less. In this mini review, [...] Read more.

Hydroarylation reactions play a pivotal role in organic chemistry due to their versatility and efficiency. In the last 10 years, the scientific production around this reaction has been very high, but in its asymmetric version, the results are less. In this mini review, selected literature examples are considered to draw attention to directions of the asymmetric hydroarylation reaction mediated by transition metal catalysts. The selected works were grouped in two main sections. In the first, we reported examples relating the narrower definition of hydroarylation, namely the metal-catalyzed processes where inactivated aryl moiety undergoes a direct functionalization via insertion of an unsaturated compound. In the second part, hydroarylation reactions take place with the use of pre-activated aryl substrates, usually aryl-iodides or aryl-boronated. Full article

(This article belongs to the Special Issue Advances in Transition Metal Catalysis)

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10 pages, 4089 KB

Open AccessArticle

5,5,5-Trichloropent-3-en-one as a Precursor of 1,3-Bi-centered Electrophile in Reactions with Arenes in Brønsted Superacid CF₃SO₃H. Synthesis of 3-Methyl-1-trichloromethylindenes

by Ivan A. Shershnev, Irina A. Boyarskaya and Aleksander V. Vasilyev

Molecules 2022, 27(19), 6675; https://doi.org/10.3390/molecules27196675 - 7 Oct 2022

Cited by 6 | Viewed by 1745

Abstract

Reactions of 5,5,5-trichloropent-3-en-2-one Cl₃CCH=CHC(=O)Me with arenes in Brønsted superacid CF₃SO₃H at room temperature for 2 h–5 days afford 3-methyl-1-trichloromethylindenes, a novel class of indene derivatives. The key reactive intermediate, O-protonated form of starting compound Cl₃ [...] Read more.

Reactions of 5,5,5-trichloropent-3-en-2-one Cl₃CCH=CHC(=O)Me with arenes in Brønsted superacid CF₃SO₃H at room temperature for 2 h–5 days afford 3-methyl-1-trichloromethylindenes, a novel class of indene derivatives. The key reactive intermediate, O-protonated form of starting compound Cl₃CCH=CHC(=OH⁺)Me, has been studied experimentally by NMR in CF₃SO₃H and theoretically by DFT calculations. The reaction proceeds through initial hydroarylation of the carbon-carbon double bond of starting CCl₃-enone, followed by cyclization onto the O-protonated carbonyl group, leading to target indenes. In general, 5,5,5-trichloropent-3-en-2-one in CF₃SO₃H acts as a 1,3-bi-centered electrophile. Full article

(This article belongs to the Section Organic Chemistry)

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18 pages, 4471 KB

Open AccessArticle

Synthesis of 3-Aryl-3-(Furan-2-yl)Propanoic Acid Derivatives, and Study of Their Antimicrobial Activity

by Mikhail V. Kalyaev, Dmitry S. Ryabukhin, Marina A. Borisova, Alexander Yu. Ivanov, Irina A. Boyarskaya, Kristina E. Borovkova, Lia R. Nikiforova, Julia V. Salmova, Nikolay V. Ul’yanovskii, Dmitry S. Kosyakov and Aleksander V. Vasilyev

Molecules 2022, 27(14), 4612; https://doi.org/10.3390/molecules27144612 - 19 Jul 2022

Cited by 10 | Viewed by 6202

Abstract

Reactions of 3-(furan-2-yl)propenoic acids and their esters with arenes in Brønsted superacid TfOH affords products of hydroarylation of the carbon–carbon double bond, 3-aryl-3-(furan-2-yl)propenoic acid derivatives. According to NMR and DFT studies, the corresponding O,C-diprotonated forms of the starting furan acids and esters should [...] Read more.

Reactions of 3-(furan-2-yl)propenoic acids and their esters with arenes in Brønsted superacid TfOH affords products of hydroarylation of the carbon–carbon double bond, 3-aryl-3-(furan-2-yl)propenoic acid derivatives. According to NMR and DFT studies, the corresponding O,C-diprotonated forms of the starting furan acids and esters should be reactive electrophilic species in these transformations. Starting compounds and their hydroarylation products, at a concentration of 64 µg/mL, demonstrate good antimicrobial activity against yeast-like fungi Candida albicans. Apart from that, these compounds suppress Escherichia coli and Staphylococcus aureus. Full article

(This article belongs to the Special Issue A Tribute to Design and Strategy in Organic Synthesis in Honour of Stephen Hanessian)

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14 pages, 2312 KB

Open AccessFeature PaperArticle

Electron-Deficient Ru(II) Complexes as Catalyst Precursors for Ethylene Hydrophenylation

by Xiaofan Jia, Songyuan Tian, Philip J. Shivokevich, W. Dean Harman, Diane A. Dickie and T. Brent Gunnoe

Inorganics 2022, 10(6), 76; https://doi.org/10.3390/inorganics10060076 - 31 May 2022

Cited by 5 | Viewed by 3415

Abstract

Ruthenium(II) complexes with the general formula TpRu(L)(NCMe)Ph (Tp = hydrido(trispyrazolyl)borate, L = CO, PMe₃, P(OCH₂)₃CEt, P(pyr)₃, P(OCH₂)₂(O)CCH₃) have previously been shown to catalyze arene alkylation via Ru-mediated arene C–H [...] Read more.

Ruthenium(II) complexes with the general formula TpRu(L)(NCMe)Ph (Tp = hydrido(trispyrazolyl)borate, L = CO, PMe₃, P(OCH₂)₃CEt, P(pyr)₃, P(OCH₂)₂(O)CCH₃) have previously been shown to catalyze arene alkylation via Ru-mediated arene C–H activation including the conversion of benzene and ethylene to ethylbenzene. Previous studies have suggested that the catalytic performance of these TpRu(II) catalysts increases with reduced electron-density at the Ru center. Herein, three new structurally related Ru(II) complexes are synthesized, characterized, and studied for possible catalytic benzene ethylation. TpRu(NO)Ph₂ exhibited low stability due to the facile elimination of biphenyl. The Ru(II) complex (Tp^Br3)Ru(NCMe)(P(OCH₂)₃CEt)Ph (Tp^Br3 = hydridotris(3,4,5-tribromopyrazol-1-yl)borate) showed no catalytic activity for the conversion of benzene and ethylene to ethylbenzene, likely due to the steric bulk introduced by the bromine substituents. (Ttz)Ru(NCMe)(P(OCH₂)₃CEt)Ph (Ttz = hydridotris(1,2,4-triazol-1-yl)borate) catalyzed approximately 150 turnover numbers (TONs) of ethylbenzene at 120 °C in the presence of Lewis acid additives. Here, we compare the activity and features of catalysis using (Ttz)Ru(NCMe)(P(OCH₂)₃CEt)Ph to previously reported catalysis based on TpRu(L)(NCMe)Ph catalyst precursors. Full article

(This article belongs to the Special Issue Inorganics: 10th Anniversary)

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13 pages, 1828 KB

Open AccessArticle

Synthesis of 4-Substituted-1,2-Dihydroquinolines by Means of Gold-Catalyzed Intramolecular Hydroarylation Reaction of N-Ethoxycarbonyl-N-Propargylanilines

by Antonio Arcadi, Andrea Calcaterra, Giancarlo Fabrizi, Andrea Fochetti, Antonella Goggiamani, Antonia Iazzetti, Federico Marrone, Vincenzo Marsicano, Giulia Mazzoccanti and Andrea Serraiocco

Molecules 2021, 26(11), 3366; https://doi.org/10.3390/molecules26113366 - 2 Jun 2021

Cited by 5 | Viewed by 3248

Abstract

An alternative Au(I)-catalyzed synthetic route to functionalized 1,2-dihydroquinolines is reported. This novel approach is based on the use of N-ethoxycarbonyl protected-N-propargylanilines as building blocks that rapidly undergo the IMHA reaction affording the 6-endo cyclization product in good to high [...] Read more.

An alternative Au(I)-catalyzed synthetic route to functionalized 1,2-dihydroquinolines is reported. This novel approach is based on the use of N-ethoxycarbonyl protected-N-propargylanilines as building blocks that rapidly undergo the IMHA reaction affording the 6-endo cyclization product in good to high yields. In the presence of N-ethoxycarbonyl-N-propargyl-meta-substituted anilines, the regiodivergent cyclization at the ortho-/para-position is achieved by the means of catalyst fine tuning. Full article

(This article belongs to the Section Organometallic Chemistry)

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16 pages, 12300 KB

Open AccessArticle

A Probable Origin of Dibenzothiophenes in Coals and Oils

by Yu Ji, Qiang Yao, Weihong Cao and Yueying Zhao

Energies 2021, 14(1), 234; https://doi.org/10.3390/en14010234 - 5 Jan 2021

Cited by 1 | Viewed by 3343

Abstract

To probe the possibility of thiophenolate as an origin of dibenzothiophenes (DBTs) and establish the detailed chemical transformations from thiophenolate to DBTs, the thermal degradation of thiophenolate has been carried out at various temperatures. The characterizations of both gaseous products and solid residues [...] Read more.

To probe the possibility of thiophenolate as an origin of dibenzothiophenes (DBTs) and establish the detailed chemical transformations from thiophenolate to DBTs, the thermal degradation of thiophenolate has been carried out at various temperatures. The characterizations of both gaseous products and solid residues indicate that DBTs together with benzene, diphenyl sulfide, and diphenyl disulfide are the major degradation products. The presence of benzene supports that the thermal degradation of thiophenolate begins with the homolysis of Ar‒H bonds. The subsequent hydroarylation followed by the elimination and cyclization reactions facilely generates DBTs. The transformation of thiophenolate to DBTs is chemically simple and highly geochemically feasible. It readily unifies the chemical pathways involved in the generation of DBTs from thiophenolate and that of dibenzofurans from phenolate in nature. Full article

(This article belongs to the Section H: Geo-Energy)

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35 pages, 4679 KB

Open AccessFeature PaperEditor’s ChoiceReview

Gold-Catalyzed Intermolecular Alkyne Hydrofunctionalizations—Mechanistic Insights

by Chin Hin Leung, Marco Baron and Andrea Biffis

Catalysts 2020, 10(10), 1210; https://doi.org/10.3390/catal10101210 - 19 Oct 2020

Cited by 51 | Viewed by 8499

Abstract

An overview of the current state of mechanistic understanding of gold-catalyzed intermolecular alkyne hydrofunctionalization reactions is presented. Moving from the analysis of the main features of the by-now-generally accepted reaction mechanism, studies and evidences pointing out the mechanistic peculiarities of these reactions using [...] Read more.

An overview of the current state of mechanistic understanding of gold-catalyzed intermolecular alkyne hydrofunctionalization reactions is presented. Moving from the analysis of the main features of the by-now-generally accepted reaction mechanism, studies and evidences pointing out the mechanistic peculiarities of these reactions using different nucleophiles HNu that add to the alkyne triple bond are presented and discussed. The effects of the nature of the employed alkyne substrate and of the gold catalyst (employed ligands, counteranions, gold oxidation state), of additional additives and of the reaction conditions are also considered. Aim of this work is to provide the reader with a detailed mechanistic knowledge of this important reaction class, which will be invaluable for rapidly developing and optimizing synthetic protocols involving a gold-catalyzed alkyne hydrofunctionalization as a reaction step. Full article

(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)

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19 pages, 6178 KB

Open AccessArticle

Base Promoted Intumescence of Phenols

by Yu Ji, Qiang Yao, Weihong Cao and Yueying Zhao

Polymers 2020, 12(2), 261; https://doi.org/10.3390/polym12020261 - 23 Jan 2020

Cited by 7 | Viewed by 3132

Abstract

The intumescent process of sodium (substituted) phenolates has been studied. The generation of hydrogen radical via a homolytic cleavage of the Ar–H bond and the subsequent hydroarylation of phenolates to cyclohexadienes along with cyclization and elimination reactions of cyclohexadienes are critical steps in [...] Read more.

The intumescent process of sodium (substituted) phenolates has been studied. The generation of hydrogen radical via a homolytic cleavage of the Ar–H bond and the subsequent hydroarylation of phenolates to cyclohexadienes along with cyclization and elimination reactions of cyclohexadienes are critical steps in the base promoted intumescence of phenols. The substituents show great influence on the intumescence of phenolates. Phenolates substituted with a weak electron donating group enable intumescence while those with an electron withdrawing group or strong electron donating group suppresses intumescence. This distinction can be justified by both electronic and steric effects of substituents on the generation of hydrogen radical and the degree of hydroarylation. Full article

(This article belongs to the Special Issue Thermal Insulating and Fire-Resistant Polymer Composites)

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28 pages, 4300 KB

Open AccessReview

Recent Advances in Synthesis of 4-Arylcoumarins

by Jong-Wha Jung, Nam-Jung Kim, Hwayoung Yun and Young Taek Han

Molecules 2018, 23(10), 2417; https://doi.org/10.3390/molecules23102417 - 20 Sep 2018

Cited by 35 | Viewed by 6839

Abstract

4-Arylcoumarins (4-aryl-2H-1-benzopyran-2-one), also known as neoflavones, comprise a minor subclass of naturally occurring flavonoids. Because of their broad-spectrum biological activities, arylcoumarins have been attracting the attention of the organic and medicinal chemistry communities, and are considered as an important privileged scaffold. [...] Read more.

4-Arylcoumarins (4-aryl-2H-1-benzopyran-2-one), also known as neoflavones, comprise a minor subclass of naturally occurring flavonoids. Because of their broad-spectrum biological activities, arylcoumarins have been attracting the attention of the organic and medicinal chemistry communities, and are considered as an important privileged scaffold. Since the development of Pechmann condensation, a classical acid-catalyzed condensation between phenol and β-keto-carboxylic acid, several versatile and efficient synthetic approaches for 4-arylcoumarins have been reported. This review summarizes recent advances in the synthesis of the 4-arylcoumarin scaffold by classifying them based on the final bond-formation type. In particular, synthetic methods executed under mild and highly efficient conditions, such as solvent-free reactions and transition metal catalysis, are highlighted. Full article

(This article belongs to the Section Organic Chemistry)

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9 pages, 782 KB

Open AccessArticle

Influence of Ionic Liquids on an Iron(III) Catalyzed Three-Component Coupling/Hydroarylation/Dehydrogenation Tandem Reaction

by Maren Muntzeck and René Wilhelm

Int. J. Mol. Sci. 2016, 17(6), 860; https://doi.org/10.3390/ijms17060860 - 1 Jun 2016

Cited by 11 | Viewed by 6667

Abstract

A three-component oxidative dehydrogenation tandem reaction via the coupling and hydroarylation of benzaldehyde, aniline and phenylacetylene to a quinoline derivate was catalyzed by an iron-containing ionic liquid. The reaction was air mediated and could be performed under neat conditions. The iron(III) of the [...] Read more.

A three-component oxidative dehydrogenation tandem reaction via the coupling and hydroarylation of benzaldehyde, aniline and phenylacetylene to a quinoline derivate was catalyzed by an iron-containing ionic liquid. The reaction was air mediated and could be performed under neat conditions. The iron(III) of the ionic liquid was the oxidizing species. Full article

(This article belongs to the Special Issue Ionic Liquids 2016 and Selected Papers from ILMAT III)

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9 pages, 227 KB

Open AccessReview

The Hydroarylation Reaction—Scope and Limitations

by Jan C. Namyslo, Jörg Storsberg, Jens Klinge, Christian Gärtner, Min-Liang Yao, Nuket Ocal and Dieter Eckhard Kaufmann

Molecules 2010, 15(5), 3402-3410; https://doi.org/10.3390/molecules15053402 - 10 May 2010

Cited by 40 | Viewed by 15535

Abstract

The synthetic potential of stereoselective, palladium-catalyzed hydro(het)arylation reactions of bi-, tri- and tetracyclic (hetero)alkenes in the presence of phospines and arsines as highly efficient ligands was studied. The mechanism of this reductive Heck reaction becomes more complex in the case of benzonorbornenes. Hydroarylation [...] Read more.

The synthetic potential of stereoselective, palladium-catalyzed hydro(het)arylation reactions of bi-, tri- and tetracyclic (hetero)alkenes in the presence of phospines and arsines as highly efficient ligands was studied. The mechanism of this reductive Heck reaction becomes more complex in the case of benzonorbornenes. Hydroarylation of diazabicyclo-[2.2.1]heptenes provides a stereoselective access to aryldiaminocyclopentanes. Electron-deficient arylpalladium complexes shift the reaction towards the product of a formal 1,2-hydrazidoarylation reaction of 1,3-cyclopentadiene by a stereoselective C-N cleavage. Due to steric reasons, rigid bicyclo[2.2.2]octenes react slower in hydroarylation reactions than the corresponding bicyclo[2.2.1]heptenes. The more flexible bicyclo[4.2.2]decene system already tends to undergo domino-Heck reactions, even under reductive conditions. When a tetracyclic cis-allylcyclopropane is carbopalladated in the presence of formates, the neighboring cyclopropane ring is attacked in the first reported example of a π,σ domino-Heck reaction. Full article

(This article belongs to the Special Issue Heck Coupling)

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7 pages, 259 KB

Open AccessArticle

Reductive Heck Reactions of N-Methyl-substituted Tricyclic Imides

by Gokce Goksu, Nuket Ocal and Dieter E. Kaufmann

Molecules 2010, 15(3), 1302-1308; https://doi.org/10.3390/molecules15031303 - 4 Mar 2010

Cited by 25 | Viewed by 8664

Abstract

The palladium-catalyzed hydroarylation of N-methyl-substituted tricyclic imides was studied in order to find a new stereoselective access to a series of new exo-aryl(hetaryl)-substituted tricyclic N-methylimides. Full article

(This article belongs to the Special Issue Heck Coupling)

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12 pages, 77 KB

Open AccessArticle

Epibatidine Alkaloid Chemistry: 5. Domino-Heck Reactions of Azabicyclic and Tricyclic Systems

by Çigdem Yolacan, Emine Bagdatli, Nüket Öcal and Dieter E. Kaufmann

Molecules 2006, 11(8), 603-614; https://doi.org/10.3390/11080603 - 16 Aug 2006

Cited by 33 | Viewed by 8710

Abstract

Palladium-catalyzed hydroarylations and additional domino reactions of aza- bicyclic and tricyclic norbornene derivatives were investigated and a series of new epibatidine analogues were synthesized. Full article

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