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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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Bobbitt JM, Eddy NA, Cady CX, Jin J, Gascon JA, Gelpí-Dominguez S, Zakrzewski J, Morton MD. Preparation of Some Homologous TEMPO Nitroxides and Oxoammonium Salts; Notes on the NMR Spectroscopy of Nitroxide Free Radicals; Observed Radical Nature of Oxoammonium Salt Solutions Containing Trace Amounts of Corresponding Nitroxides in an Equilibrium Relationship. J Org Chem 2017; 82:9279-9290. [DOI: 10.1021/acs.joc.7b00846] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- James M. Bobbitt
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Nicholas A. Eddy
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Clyde X. Cady
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Jing Jin
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Jose A. Gascon
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Svetlana Gelpí-Dominguez
- Department
of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Jerzy Zakrzewski
- Institute of Industrial Organic Chemistry, Annopol 6, 03-236 Warsaw, Poland
| | - Martha D. Morton
- Department
of Chemistry, University of Nebraska, Lincoln, NE 68588, United States
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Cao Q, Dornan LM, Rogan L, Hughes NL, Muldoon MJ. Aerobic oxidation catalysis with stable radicals. Chem Commun (Camb) 2015; 50:4524-43. [PMID: 24667871 DOI: 10.1039/c3cc47081d] [Citation(s) in RCA: 258] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Selective oxidation reactions are challenging when carried out on an industrial scale. Many traditional methods are undesirable from an environmental or safety point of view. There is a need to develop sustainable catalytic approaches that use molecular oxygen as the terminal oxidant. This review will discuss the use of stable radicals (primarily nitroxyl radicals) in aerobic oxidation catalysis. We will discuss the important advances that have occurred in recent years, highlighting the catalytic performance, mechanistic insights and the expanding synthetic utility of these catalytic systems.
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Affiliation(s)
- Qun Cao
- School of Chemistry and Chemical Engineering, Queen's University Belfast, David Keir Building, Stranmillis Road, Belfast, UKBT9 5AG.
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Shibuya M. [Development of versatile oxidation systems based on the design of oxoammonium salts]. YAKUGAKU ZASSHI 2012; 132:1131-43. [PMID: 23037698 DOI: 10.1248/yakushi.12-00203] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Organic nitroxyl radical catalysts have recently attracted great attention because they realize efficient alcohol oxidation under mild and environmentally benign conditions. A representative of this class is 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). We have also developed 2-azaadamantane N-oxyls (AZADOs) as highly efficient oxidation catalysts. These nitroxyl radicals are generally oxidized by a cooxidant to generate oxoammonium salts, which are active species for alcohol oxidation. In the oxidation systems presented in this paper, we focus on the differences between these two species in terms of oxidation state and counter anion. Herein, the effects of a counter anion of an oxoammonium species on its reaction selectivity are shown. On the basis of the control of the counter anion, we have developed catalytic oxidative rearrangement of tertiary allylic alcohols to β-substituted α,β-unsaturated carbonyl compounds. Moreover, we have developed novel useful oxidation systems utilizing a catalytic oxoammonium salt; namely, a one-pot oxidation of primary alcohols to carboxylic acids and an aerobic alcohol oxidation.
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Affiliation(s)
- Masatoshi Shibuya
- Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aoba, Aramaki, Sendai, Japan.
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Shibuya M, Osada Y, Sasano Y, Tomizawa M, Iwabuchi Y. Highly Efficient, Organocatalytic Aerobic Alcohol Oxidation. J Am Chem Soc 2011; 133:6497-500. [DOI: 10.1021/ja110940c] [Citation(s) in RCA: 160] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Masatoshi Shibuya
- Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama 6-3, Sendai 980-8578, Japan
| | - Yuji Osada
- Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama 6-3, Sendai 980-8578, Japan
| | - Yusuke Sasano
- Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama 6-3, Sendai 980-8578, Japan
| | - Masaki Tomizawa
- Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama 6-3, Sendai 980-8578, Japan
| | - Yoshiharu Iwabuchi
- Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama 6-3, Sendai 980-8578, Japan
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Gartshore CJ, Lupton DW. Readily Accessible Oxazolidine Nitroxyl Radicals: Bifunctional Cocatalysts for Simplified Copper Based Aerobic Oxidation. Adv Synth Catal 2010. [DOI: 10.1002/adsc.201000627] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Kayen AHM, de Boer K, de Boer TJ. C-nitroso compounds. Part XXVII. The lability of chlorine in (1-chloroalkyl)nitroxides. Reaction with tri-n-butyltin hydride and nitric oxide. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/recl.19770960102] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Hamdani M, Scholler D, Bouquant J, Feigenbaum A. Selective formation of aminoxyls or oxaziridines by oxidation of 2,2,4,4-tetrasubstituted oxazolidines. Tetrahedron 1996. [DOI: 10.1016/0040-4020(95)00899-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Alberti A, Carloni P, Greci L, Stipa P, Neri C. Antioxidants and light stabilizers. Part 2. On the thermal stability of indolinonic nitroxides. Polym Degrad Stab 1993. [DOI: 10.1016/0141-3910(93)90098-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Valić S, Rakvin B, Veksli Z, Pečar S. Slow molecular motion of different spin probes in a model glycerol—water matrix studied by double modulation ESR. Chem Phys Lett 1992. [DOI: 10.1016/0009-2614(92)85018-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Banerjee S, Desai UR, Trivedi GK. Synthesis of 2'-(3α-benzyloxy-24-norcholan-23-yl)-2',4',4'-trimethyl- 4',5'-dihydrooxazoline-n-oxyl - a new potential spin probe for biomembranes. Tetrahedron 1992. [DOI: 10.1016/s0040-4020(01)80586-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Chemical and electrochemical synthesis of quinoneimine n-oxides from indolinone-3-arylimino nitroxide radicals. Tetrahedron 1988. [DOI: 10.1016/s0040-4020(01)85929-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Pečar S, Sorg B, Schara M, Hecker E. Spin-labeled phorbol esters and their interaction with cellular membranes. I. Synthesis of spin-labeled phorbol-12, 13-diesters and related compounds. Chem Phys Lipids 1984. [DOI: 10.1016/0009-3084(84)90021-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Moad G, Rizzardo E, Solomon DH. The reaction of acyl peroxides with 2,2,6,6-tetramethylpiperidinyl-1-oxy. Tetrahedron Lett 1981. [DOI: 10.1016/s0040-4039(01)90265-5] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Michon J, Rassat A. Nitroxydes 94 : decomposition thermique d'un radical oxazolidine-oxyle. Tetrahedron Lett 1980. [DOI: 10.1016/s0040-4039(00)93654-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Smith DL, Spencer TA. Synthesis and photolysis of doxyl derivatives of 5β-androstan-3-ones. J Heterocycl Chem 1979. [DOI: 10.1002/jhet.5570160441] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Marai L, Myher JJ, Kuksis A. Identification of isomeric doxyl stearic acids by gas-liquid chromatography and mass spectrometry. Chem Phys Lipids 1976; 17:213-21. [PMID: 186203 DOI: 10.1016/0009-3084(76)90066-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Direct probe and GC/MS spectra were determined for the isomeric 4- to 16-doxyl stearic acids and their methyl and silyl esters in pure form and in mixture with natural fatty acids and their esters. The base peak for all free and esterified doxyl stearic acids was at m/e 281. The methyl esters of all isomers gave nearly identical fragments in the high mass regions having M+ at m/e 398 with intensities of 2-3%. The isomers were identified on the basis of the fragments retaining the doxyl group, which had positive charge and were different for each compound. It was shown that the fragment m/e 281 may be used to identify and quantitate the stearate derivatives in presence of natural fatty acids. The silyl esters of the doxyl stearates gave complex mass spectra. The isomeric doxyl stearates were resolved by GLC on 3 ft. glass columns containing 1% SE-30 packing as methyl esters.
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