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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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Šafář P, Marchalín Š, Cvečko M, Moncol J, Dujnič V, Šoral M, Daïch A. Synthesis and sequential diastereoselective incorporation of hydroxyl groups into hexahydrofuro[3,2-f]indolizin-7(2H)-one to give mono-, di- and tetra-hydroxyfuroindolizidines. Org Biomol Chem 2020; 18:6384-6393. [PMID: 32756691 DOI: 10.1039/d0ob00896f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Dihydrofuro[2,3-f]indolizidinone obtained from biosourced reagents even at multigram-scale was used as an advanced building-block with up to five points of chemical diversification. This resulted in the sequential synthesis of a series of mono-, di- and tetra-hydroxyfuranoindolizidines belonging to a very scarce and elaborate tetrahydrofuran-fused indolizidine family with up to six controlled stereogenic centers. These sequences include, among others, diastereoselective olefin epoxidation, stereoselective epoxide ring opening into tetrahydrofuran trans-diols, their protection as an ester or acetonide, and lactam carbonyl reduction ultimately followed by acetate or acetonide deprotection.
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Affiliation(s)
- Peter Šafář
- Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-81237 Bratislava, Slovakia.
| | - Štefan Marchalín
- Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-81237 Bratislava, Slovakia. and Normandie Univ, UNILEHAVRE, CNRS, URCOM, 76600 Le Havre, France.
| | - Matej Cvečko
- Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-81237 Bratislava, Slovakia.
| | - Ján Moncol
- Department of Inorganic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-81237 Bratislava, Slovakia
| | - Viera Dujnič
- Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38, Bratislava, Slovakia
| | - Michal Šoral
- Central Laboratories, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, SK-81237 Bratislava, Slovakia
| | - Adam Daïch
- Normandie Univ, UNILEHAVRE, CNRS, URCOM, 76600 Le Havre, France.
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Petsi M, Zografos AL. 2,5-Diketopiperazine Catalysts as Activators of Dioxygen in Oxidative Processes. ACS Catal 2020. [DOI: 10.1021/acscatal.0c01847] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Marina Petsi
- Department of Chemistry, Main University Campus, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
| | - Alexandros L. Zografos
- Department of Chemistry, Main University Campus, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
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Dokli I, Pohl R, Klepetářová B, Jahn U. First total synthesis of ent-asperparaline C and assignment of the absolute configuration of asperparaline C. Chem Commun (Camb) 2019; 55:3931-3934. [DOI: 10.1039/c9cc00945k] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The first asymmetric total synthesis of a member of the asperparaline family was accomplished and the unknown absolute configuration of asperparaline C has been determined to be all-(S).
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Affiliation(s)
- Irena Dokli
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences
- 16610 Prague 6
- Czech Republic
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences
- 16610 Prague 6
- Czech Republic
| | - Blanka Klepetářová
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences
- 16610 Prague 6
- Czech Republic
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences
- 16610 Prague 6
- Czech Republic
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Romero KJ, Galliher MS, Pratt DA, Stephenson CRJ. Radicals in natural product synthesis. Chem Soc Rev 2018; 47:7851-7866. [PMID: 30101272 PMCID: PMC6205920 DOI: 10.1039/c8cs00379c] [Citation(s) in RCA: 164] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Free radical intermediates have intrigued chemists since their discovery, and an ever-increasing appreciation for their unique reactivity has resulted in the widespread utilization of these species throughout the field of chemical synthesis. This is most evident from the recent surge in the application of intermolecular radical reactions that feature in complex molecule syntheses. This tutorial review will discuss the diverse methods utilized for radical generation and reactivity to form critical bonds in natural product total synthesis. In particular, stabilized (e.g. benzyl) and persistent (e.g. TEMPO) radicals will be the primary focus.
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Affiliation(s)
- Kevin J Romero
- Department of Chemistry, University of Michigan, 930 N. University Ave, Ann Arbor, MI 48109, USA.
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6
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Amatov T, Jangra H, Pohl R, Cisařová I, Zipse H, Jahn U. Unique Stereoselective Homolytic C-O Bond Activation in Diketopiperazine-Derived Alkoxyamines by Adjacent Amide Pyramidalization. Chemistry 2018; 24:15336-15345. [PMID: 30092124 DOI: 10.1002/chem.201803284] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 08/02/2018] [Indexed: 12/12/2022]
Abstract
Simple monocyclic diketopiperazine (DKP)-derived alkoxyamines exhibit unprecedented activation of a remote C-O bond for homolysis by amide distortion. The combination of strain-release-driven amide planarization and the persistent radical effect (PRE) enables a unique, irreversible, and quantitative trans→cis isomerization under much milder conditions than typically observed for such homolysis-limited reactions. This isomerization is shown to be general and independent of the steric and electronic nature of both the amino acid side chains and the substituents at the DKP nitrogen atoms. Homolysis rate constants are determined, and they significantly differ for both the labile trans diastereomers and the stable cis diastereomers. To reveal the factors influencing this unusual process, structural features of the kinetic trans diastereomers and thermodynamic cis diastereomers are investigated in the solid state and in solution. X-ray crystallographic analysis and computational studies indicate substantial distortion of the amide bond from planarity in the trans-alkoxyamines, and this is believed to be the cause for the facile and quantitative isomerization. Thus, these amino-acid-derived alkoxyamines are the first examples that exhibit a large thermodynamic preference for one diastereomer over the other upon thermal homolysis, and this allows controlled switching of configurations and configurational cycling.
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Affiliation(s)
- Tynchtyk Amatov
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610, Prague, Czech Republic.,Ludwig Maximilian University, Department of Chemistry, Butenandstrasse 5-13, 81377, München, Germany
| | - Harish Jangra
- Ludwig Maximilian University, Department of Chemistry, Butenandstrasse 5-13, 81377, München, Germany
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610, Prague, Czech Republic
| | - Ivana Cisařová
- Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 12843, Prague, Czech Republic
| | - Hendrik Zipse
- Ludwig Maximilian University, Department of Chemistry, Butenandstrasse 5-13, 81377, München, Germany
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610, Prague, Czech Republic
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Amatov T, Pohl R, Cisařová I, Jahn U. Sequential Oxidative and Reductive Radical Cyclization Approach toward Asperparaline C and Synthesis of Its 8-Oxo Analogue. Org Lett 2017; 19:1152-1155. [PMID: 28207265 DOI: 10.1021/acs.orglett.7b00187] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The most advanced approach, so far, to the asperparalines is developed. Consecutive oxidative and reductive radical cyclizations serve as the key steps to stereoselectively access the complex fully elaborated skeleton containing the cyclopentane and spiro-succinimide units.
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Affiliation(s)
- Tynchtyk Amatov
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences , Flemingovo namesti 2, 16610 Prague 6, Czech Republic
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences , Flemingovo namesti 2, 16610 Prague 6, Czech Republic
| | - Ivana Cisařová
- Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague , Hlavova 8, 12843 Prague 2, Czech Republic
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences , Flemingovo namesti 2, 16610 Prague 6, Czech Republic
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