1
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Abstract
Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.
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Affiliation(s)
- Dirk Leifert
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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2
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Di Berto Mancini M, Tabussi A, Bernardini M, Lanzalunga O. Oxidations of aromatic sulfides promoted by the phthalimide N-oxyl radical (PINO). J Sulphur Chem 2023. [DOI: 10.1080/17415993.2023.2182160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
Affiliation(s)
- Marika Di Berto Mancini
- Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza” and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione, c/o Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza”, Rome, Italy
| | - Alessandro Tabussi
- Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza” and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione, c/o Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza”, Rome, Italy
| | - Marianna Bernardini
- Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza” and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione, c/o Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza”, Rome, Italy
| | - Osvaldo Lanzalunga
- Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza” and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione, c/o Dipartimento di Chimica, Università degli Studi di Roma “La Sapienza”, Rome, Italy
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3
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Zhou J, Jia M, Song M, Huang Z, Steiner A, An Q, Ma J, Guo Z, Zhang Q, Sun H, Robertson C, Bacsa J, Xiao J, Li C. Chemoselective Oxyfunctionalization of Functionalized Benzylic Compounds with a Manganese Catalyst. Angew Chem Int Ed Engl 2022; 61:e202205983. [PMID: 35594169 PMCID: PMC9400980 DOI: 10.1002/anie.202205983] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Indexed: 11/06/2022]
Abstract
Whilst allowing for easy access to synthetically versatile motifs and for modification of bioactive molecules, the chemoselective benzylic oxidation reactions of functionalized alkyl arenes remain challenging. Reported in this study is a new non‐heme Mn catalyst stabilized by a bipiperidine‐based tetradentate ligand, which enables methylene oxidation of benzylic compounds by H2O2, showing high activity and excellent chemoselectivity under mild conditions. The protocol tolerates an unprecedentedly wide range of functional groups, including carboxylic acid and derivatives, ketone, cyano, azide, acetate, sulfonate, alkyne, amino acid, and amine units, thus providing a low‐cost, more sustainable and robust pathway for the facile synthesis of ketones, increase of complexity of organic molecules, and late‐stage modification of drugs.
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Affiliation(s)
- Jimei Zhou
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Minxian Jia
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Menghui Song
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Zhiliang Huang
- Department of Chemistry University of Liverpool Liverpool L69 7ZD UK
| | - Alexander Steiner
- Department of Chemistry University of Liverpool Liverpool L69 7ZD UK
| | - Qidong An
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Jianwei Ma
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Zhiyin Guo
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Qianqian Zhang
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Huaming Sun
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
| | - Craig Robertson
- Department of Chemistry University of Liverpool Liverpool L69 7ZD UK
| | - John Bacsa
- Department of Chemistry Emory University 1515 Dickey Dr. Atlanta GA 30322 USA
| | - Jianliang Xiao
- Department of Chemistry University of Liverpool Liverpool L69 7ZD UK
| | - Chaoqun Li
- Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education and School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an 710119 China
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4
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Zhou J, Jia M, Song M, Huang Z, Steiner A, An Q, Ma J, Guo Z, Zhang Q, Sun H, Robertson CM, Bacsa J, Xiao J, Li C. Chemoselective Oxyfunctionalization of Functionalized Benzylic Compounds with a Manganese Catalyst. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202205983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jimei Zhou
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an CHINA
| | - Minxian Jia
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an UNITED KINGDOM
| | - Menghui Song
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an UNITED KINGDOM
| | - Zhiliang Huang
- University of Liverpool Department of Chemistry UNITED KINGDOM
| | | | - Qidong An
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an UNITED KINGDOM
| | - Jianwei Ma
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an UNITED KINGDOM
| | - Zhiyin Guo
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an UNITED KINGDOM
| | - Qianqian Zhang
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an UNITED KINGDOM
| | - Huaming Sun
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an UNITED KINGDOM
| | | | - John Bacsa
- Emory University Department of Chemistry UNITED KINGDOM
| | - Jianliang Xiao
- University of Liverpool Department of Chemistry Oxford Street L69 7ZD Liverpool UNITED KINGDOM
| | - Chaoqun Li
- Shaanxi Normal University School of Chemistry & Chemical Engineering Xi'an CHINA
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5
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Kato T, Maruoka K. Selective functionalization of benzylic C-H bonds of two different benzylic ethers by bowl-shaped N-hydroxyimide derivatives as efficient organoradical catalysts. Chem Commun (Camb) 2021; 58:1021-1024. [PMID: 34951412 DOI: 10.1039/d1cc06425h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A highly efficient, site-selective benzylic C-H bond amination of two different benzylic ether substrates was described by using bowl-shaped N-hydroxyimide organoradical catalysts with diethyl azodicarboxylate. The synthetic utility of this approach is demonstrated by the subsequent transformation of the amination products into the corresponding aldehydes and alkylhydrazines.
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Affiliation(s)
- Terumasa Kato
- School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China.,Guangdong Provincial Key Laboratory of Plant Resources Biorefinery, Guangdong University of Technology, Guangzhou 510006, China.,Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo, Kyoto 606-8501, Japan.
| | - Keiji Maruoka
- School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China.,Guangdong Provincial Key Laboratory of Plant Resources Biorefinery, Guangdong University of Technology, Guangzhou 510006, China.,Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo, Kyoto 606-8501, Japan.
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6
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Di Berto Mancini M, Del Gelsomino A, Di Stefano S, Frateloreto F, Lapi A, Lanzalunga O, Olivo G, Sajeva S. Change of Selectivity in C-H Functionalization Promoted by Nonheme Iron(IV)-oxo Complexes by the Effect of the N-hydroxyphthalimide HAT Mediator. ACS OMEGA 2021; 6:26428-26438. [PMID: 34661000 PMCID: PMC8515612 DOI: 10.1021/acsomega.1c03679] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Accepted: 08/17/2021] [Indexed: 06/13/2023]
Abstract
A kinetic analysis of the hydrogen atom transfer (HAT) reactions from a series of organic compounds to the iron(IV)-oxo complex [(N4Py)FeIV(O)]2+ and to the phthalimide N-oxyl radical (PINO) has been carried out. The results indicate that a higher activating effect of α-heteroatoms toward the HAT from C-H bonds is observed with the more electrophilic PINO radical. When the N-hydroxy precursor of PINO, N-hydroxyphthalimide (NHPI), is used as a HAT mediator in the oxidation promoted by [(N4Py)FeIV(O)]2+, significant differences in terms of selectivity have been found. Product studies of the competitive oxidations of primary and secondary aliphatic alcohols (1-decanol, cyclopentanol, and cyclohexanol) with alkylaromatics (ethylbenzene and diphenylmethane) demonstrated that it is possible to modify the selectivity of the oxidations promoted by [(N4Py)FeIV(O)]2+ in the presence of NHPI. In fact, alkylaromatic substrates are more reactive in the absence of the mediator while alcohols are preferably oxidized in the presence of NHPI.
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Affiliation(s)
- Marika Di Berto Mancini
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
| | - Andrea Del Gelsomino
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
| | - Stefano Di Stefano
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
| | - Federico Frateloreto
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
| | - Andrea Lapi
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
| | - Osvaldo Lanzalunga
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
- CIRCC
Interuniversity Consortium Chemical Reactivity and Catalysis, Via Celso Ulpiani 27, 70126 Bari, Italy
| | - Giorgio Olivo
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
| | - Stefano Sajeva
- Dipartimento
di Chimica and Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione
Meccanismi di Reazione, c/o Dipartimento di Chimica, Università di Roma “La Sapienza”, P.le A. Moro, 5, I-00185 Rome, Italy
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7
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Xie P, Xue C, Du D, Shi S. Photo-induced oxidative cleavage of C-C double bonds for the synthesis of biaryl methanone via CeCl 3 catalysis. Org Biomol Chem 2021; 19:6781-6785. [PMID: 34312650 DOI: 10.1039/d1ob01002f] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A Ce-catalyzed strategy is developed to produce biaryl methanones via photooxidative cleavage of C-C double bonds at room temperature. This reaction is performed under air and demonstrates high activity as well as functional group tolerance. A synergistic Ce/ROH catalytic mechanism is also proposed based on the experimental observations. This protocol should be the first successful Ce-catalyzed photooxidation reaction of olefins with air as the oxidant, which would provide inspiration for the development of novel Ce-catalyzed photochemical synthesis processes.
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Affiliation(s)
- Pan Xie
- College of Chemistry and Chemistry Engineering, Shaanxi Key Laboratory of Chemistry Additives for Industry, Shaanxi University of Science & Technology, Xi'an 710021, China.
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8
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Capaldo L, Ravelli D, Fagnoni M. Direct Photocatalyzed Hydrogen Atom Transfer (HAT) for Aliphatic C-H Bonds Elaboration. Chem Rev 2021; 122:1875-1924. [PMID: 34355884 PMCID: PMC8796199 DOI: 10.1021/acs.chemrev.1c00263] [Citation(s) in RCA: 318] [Impact Index Per Article: 106.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
![]()
Direct photocatalyzed
hydrogen atom transfer (d-HAT) can be considered
a method of choice for the elaboration of
aliphatic C–H bonds. In this manifold, a photocatalyst (PCHAT) exploits the energy of a photon to trigger the homolytic
cleavage of such bonds in organic compounds. Selective C–H
bond elaboration may be achieved by a judicious choice of the hydrogen
abstractor (key parameters are the electronic character and the molecular
structure), as well as reaction additives. Different are the classes
of PCsHAT available, including aromatic ketones, xanthene
dyes (Eosin Y), polyoxometalates, uranyl salts, a metal-oxo porphyrin
and a tris(amino)cyclopropenium radical dication. The processes (mainly
C–C bond formation) are in most cases carried out under mild
conditions with the help of visible light. The aim of this review
is to offer a comprehensive survey of the synthetic applications of
photocatalyzed d-HAT.
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Affiliation(s)
- Luca Capaldo
- Flow Chemistry Group, Van't Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Davide Ravelli
- PhotoGreen Lab, Department of Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy
| | - Maurizio Fagnoni
- PhotoGreen Lab, Department of Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy
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9
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1,1,1,3,3,3-Hexafluoroisopropanol as an efficient medium for the room temperature oxidation of styrenes to benzaldehydes. Tetrahedron Lett 2020. [DOI: 10.1016/j.tetlet.2020.152527] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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10
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Chen W, Tang H, Wang W, Fu Q, Luo J. Catalytic Aerobic Dehydrogenatin of
N
‐Heterocycles by
N
‐Hydoxyphthalimide. Adv Synth Catal 2020. [DOI: 10.1002/adsc.202000767] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Weidong Chen
- School of Materials Science and Chemical Engineering Ningbo University Ningbo Zhejiang 315211 People's Republic of China
| | - Hao Tang
- School of Materials Science and Chemical Engineering Ningbo University Ningbo Zhejiang 315211 People's Republic of China
| | - Weilin Wang
- School of Materials Science and Chemical Engineering Ningbo University Ningbo Zhejiang 315211 People's Republic of China
| | - Qiang Fu
- School of Pharmacy Southwest Medical University Luzhou 610041 People's Republic of China
| | - Junfei Luo
- School of Materials Science and Chemical Engineering Ningbo University Ningbo Zhejiang 315211 People's Republic of China
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11
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Barbieri A, Lanzalunga O, Lapi A, Di Stefano S. N-Hydroxyphthalimide: A Hydrogen Atom Transfer Mediator in Hydrocarbon Oxidations Promoted by Nonheme Iron(IV)-Oxo Complexes. J Org Chem 2019; 84:13549-13556. [PMID: 31532207 DOI: 10.1021/acs.joc.9b01813] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The oxidation of a series of hydrocarbons by the nonheme iron(IV)-oxo complex [(N4Py)FeIV═O]2+ is efficiently mediated by N-hydroxyphthalimide. The increase of reactivity is associated to the oxidation of the mediator to the phthalimide N-oxyl radical, which efficiently abstracts a hydrogen atom from the substrates, regenerating the mediator in its reduced form.
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Affiliation(s)
- Alessia Barbieri
- Dipartimento di Chimica , Università di Roma "La Sapienza", Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione , P.le A. Moro , 5 I-00185 Rome , Italy
| | - Osvaldo Lanzalunga
- Dipartimento di Chimica , Università di Roma "La Sapienza", Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione , P.le A. Moro , 5 I-00185 Rome , Italy
| | - Andrea Lapi
- Dipartimento di Chimica , Università di Roma "La Sapienza", Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione , P.le A. Moro , 5 I-00185 Rome , Italy
| | - Stefano Di Stefano
- Dipartimento di Chimica , Università di Roma "La Sapienza", Istituto CNR per i Sistemi Biologici (ISB-CNR), Sezione Meccanismi di Reazione , P.le A. Moro , 5 I-00185 Rome , Italy
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12
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Ticconi B, Mazzonna M, Lanzalunga O, Lapi A. Oxidation of α-amino acids promoted by the phthalimide N-oxyl radical: A kinetic and product study. Tetrahedron 2019. [DOI: 10.1016/j.tet.2019.05.026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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13
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Bietti M. Anwendung von Mediumeffekten in Aktivierungs‐ und Deaktivierungsstrategien zur selektiven Funktionalisierung aliphatischer C‐H‐Bindungen. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201804929] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Massimo Bietti
- Dipartimento di Scienze e Tecnologie ChimicheUniversità “Tor Vergata” Via della Ricerca Scientifica, 1 I-00133 Rome Italien
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14
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Bietti M. Activation and Deactivation Strategies Promoted by Medium Effects for Selective Aliphatic C-H Bond Functionalization. Angew Chem Int Ed Engl 2018; 57:16618-16637. [PMID: 29873935 DOI: 10.1002/anie.201804929] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 05/31/2018] [Indexed: 12/17/2022]
Abstract
Selective functionalization of unactivated aliphatic C-H bonds represents an important goal of modern synthetic chemistry. Differentiating between such bonds in organic molecules with high levels of selectivity remains a crucial issue, and a profound understanding of even the subtlest reactivity trends is needed. Among the methods that have been developed, those based on hydrogen atom transfer (HAT) have attracted considerable interest. Within this framework, medium effects have proved effective in altering the reactivity and site selectivity in synthetically useful C-H functionalization procedures. In this Review, the mechanistic features behind the available strategies are discussed. It is shown that hydrogen bonding and acid-base interactions can promote C-H bond activation or deactivation toward HAT reagents, thereby providing fine-control over the site selectivity and product chemoselectivity as well as useful guidelines for future development and applications.
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Affiliation(s)
- Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1, I-00133, Rome, Italy
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