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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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Yang JS, Lu K, Li CX, Zhao ZH, Zhang XM, Zhang FM, Tu YQ. Chiral 1,2,3-Triazolium Salt Catalyzed Asymmetric Mono- and Dialkylation of 2,5-Diketopiperazines with the Construction of Tetrasubstituted Carbon Centers. Angew Chem Int Ed Engl 2022; 61:e202114129. [PMID: 34981881 DOI: 10.1002/anie.202114129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Indexed: 11/07/2022]
Abstract
Novel asymmetric mono- and dialkylation reactions of α-substituted 2,5-diketopiperazines catalyzed by new chiral spirocyclic-amide-derived triazolium organocatalysts have been developed, resulting in a range of enantioenriched 2,5-diketopiperazine derivatives containing one or two tetrasubstituted carbon stereocenters. The reactions feature high yields (up to 98%), and excellent cis-diastereo- and enantioselectivities (up to >20:1 dr, >99 % ee), and they provide a new asymmetric synthetic approach to important functionalized 2,5-diketopiperazine skeletons. Furthermore, a possible reaction mechanism was proposed based on both control experiments and extensive DFT calculations.
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Affiliation(s)
- Ju-Song Yang
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R. China
| | - Ka Lu
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R. China
| | - Chen-Xiao Li
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R. China
| | - Zu-Hang Zhao
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R. China
| | - Xiao-Ming Zhang
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R. China
| | - Fu-Min Zhang
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R. China
| | - Yong-Qiang Tu
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R. China.,School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, Shanghai Jiao Tong University, Shanghai, 200240, P. R. China
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3
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Fang X, Zhang N, Chen SC, Luo T. Scalable Total Synthesis of (-)-Triptonide: Serendipitous Discovery of a Visible-Light-Promoted Olefin Coupling Initiated by Metal-Catalyzed Hydrogen Atom Transfer (MHAT). J Am Chem Soc 2022; 144:2292-2300. [PMID: 35089705 DOI: 10.1021/jacs.1c12525] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
An efficient and scalable total synthesis of (-)-triptonide is accomplished based on a metal-catalyzed hydrogen atom transfer (MHAT)-initiated radical cyclization. During the optimization of the key step, we discovered that blue LEDs significantly promoted the efficiency of reaction initiated by Co(TPP)-catalyzed MHAT. Further exploration and optimization of this catalytic system led to development of a dehydrogenative MHAT-initiated Giese reaction.
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Affiliation(s)
- Xianhe Fang
- Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China.,Institute of Molecular Physiology, Shenzhen Bay Laboratory, Shenzhen, Guangdong 518055, China
| | - Nan Zhang
- Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
| | - Si-Cong Chen
- Key Laboratory of Bioorganic Chemistry and Molecular Engineering, Ministry of Education and Beijing National Laboratory for Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Tuoping Luo
- Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China.,Key Laboratory of Bioorganic Chemistry and Molecular Engineering, Ministry of Education and Beijing National Laboratory for Molecular Science, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.,Institute of Molecular Physiology, Shenzhen Bay Laboratory, Shenzhen, Guangdong 518055, China
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4
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Yang J, Lu K, Li C, Zhao Z, Zhang X, Zhang F, Tu Y. Chiral 1,2,3‐Triazolium Salt Catalyzed Asymmetric Mono‐ and Dialkylation of 2,5‐Diketopiperazines with the Construction of Tetrasubstituted Carbon Centers. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202114129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Ju‐Song Yang
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
| | - Ka Lu
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
| | - Chen‐Xiao Li
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
| | - Zu‐Hang Zhao
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
| | - Xiao‐Ming Zhang
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
| | - Fu‐Min Zhang
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
| | - Yong‐Qiang Tu
- State Key Laboratory of Applied Organic Chemistry and College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
- School of Chemistry and Chemical Engineering Frontiers Science Center for Transformative Molecules Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs Shanghai Jiao Tong University Shanghai 200240 P. R. China
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5
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Klychnikov MK, Pohl R, Císařová I, Jahn U. α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams. Beilstein J Org Chem 2021; 17:688-704. [PMID: 33777244 PMCID: PMC7961876 DOI: 10.3762/bjoc.17.58] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 02/23/2021] [Indexed: 11/23/2022] Open
Abstract
Pyrrolidones are common heterocyclic fragments in various biologically active compounds. Here, a two-step radical-based approach to γ-lactams bearing three to four stereocenters starting from epoxides, N-allylic silylacetamides and TEMPO is reported. The sequence starts with a new tandem nucleophilic substitution/Brook rearrangement/single electron transfer-induced radical oxygenation furnishing orthogonally protected α,γ-dioxygenated N-allylamides with wide scope, mostly good yields, and partly good diastereo- and enantioselectivity for defined combinations of chiral epoxides and chiral amides. This represents a very rare example of an oxidative geminal C-C/C-O difunctionalization next to carbonyl groups. The resulting dioxygenated allylic amides are subsequently subjected to persistent radical effect-based 5-exo-trig radical cyclization reactions providing functionalized pyrrolidones in high yields as diastereomeric mixtures. They converge to 3,4-trans-γ-lactams by base-mediated equilibration, which can be easily further diversified. Stereochemical models for both reaction types were developed.
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Affiliation(s)
- Mikhail K Klychnikov
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo náměstí 2, 16610 Prague 6, Czech Republic
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo náměstí 2, 16610 Prague 6, Czech Republic
| | - Ivana Císařová
- Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 12843 Prague 2, Czech Republic
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo náměstí 2, 16610 Prague 6, Czech Republic
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6
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Wu J, Ma Z. Metal-hydride hydrogen atom transfer (MHAT) reactions in natural product synthesis. Org Chem Front 2021. [DOI: 10.1039/d1qo01139a] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Functionalization of olefins has been an important transformation in synthetic chemistry. This review will focus on the natural product synthesis employing the MHAT reaction as the key strategy.
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Affiliation(s)
- Jinghua Wu
- Key Lab of Functional Molecular Engineering of Guangdong Province, School of Chemistry & Chemical Engineering, South China University of Technology, Wushan Road-381, Guangzhou 510641, People's Republic of China
| | - Zhiqiang Ma
- Key Lab of Functional Molecular Engineering of Guangdong Province, School of Chemistry & Chemical Engineering, South China University of Technology, Wushan Road-381, Guangzhou 510641, People's Republic of China
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7
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Šimek M, Bártová K, Pohl R, Císařová I, Jahn U. Tandemreaktionen aus anionischer Oxy‐Cope‐Umlagerung und Oxygenierung als vielseitiger Zugang zu verschiedenartigen Gerüsten. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201916188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Michal Šimek
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
| | - Kateřina Bártová
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
| | - Radek Pohl
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
| | - Ivana Císařová
- Institut für Anorganische ChemieNaturwissenschaftliche FakultätKarls-Universität Prag Hlavova 2030/8 12843 Prag 2 Czech republic
| | - Ullrich Jahn
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
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8
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Šimek M, Bártová K, Pohl R, Císařová I, Jahn U. Tandem Anionic oxy-Cope Rearrangement/Oxygenation Reactions as a Versatile Method for Approaching Diverse Scaffolds. Angew Chem Int Ed Engl 2020; 59:6160-6165. [PMID: 31994304 DOI: 10.1002/anie.201916188] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Indexed: 12/29/2022]
Abstract
Tandem anionic oxy-Cope rearrangement/radical oxygenation reactions provide δ,ϵ-unsaturated α-(aminoxy) carbonyl compounds, which serve as convenient precursors to diverse compound classes. Functionalized carbocycles are accessible by very rare all-carbon 5-endo-trig cyclizations, but also common 5-exo-trig radical cyclizations, based on the persistent radical effect. The tandem reactions can be further extended by highly diastereoselective allylation or reduction steps to give complex scaffolds.
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Affiliation(s)
- Michal Šimek
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
| | - Kateřina Bártová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
| | - Ivana Císařová
- Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 12843, Prague 2, Czech Republic
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
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9
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Klychnikov MK, Pohl R, Císařová I, Jahn U. Application of the Brook Rearrangement in Tandem with Single Electron Transfer Oxidative and Radical Processes. European J Org Chem 2020. [DOI: 10.1002/ejoc.202000126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Mikhail K. Klychnikov
- Institute of Organic Chemistry and Biochemistry; Czech Academy of Sciences; Flemingovo náměstí 2 16610 Prague 6 Czech Republic
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry; Czech Academy of Sciences; Flemingovo náměstí 2 16610 Prague 6 Czech Republic
| | - Ivana Císařová
- Department of Inorganic Chemistry; Faculty of Science; Charles University in Prague; Hlavova 2030/8 12843 Prague 2 Czech Republic
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry; Czech Academy of Sciences; Flemingovo náměstí 2 16610 Prague 6 Czech Republic
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Kim D, Rahaman SMW, Mercado BQ, Poli R, Holland PL. Roles of Iron Complexes in Catalytic Radical Alkene Cross-Coupling: A Computational and Mechanistic Study. J Am Chem Soc 2019; 141:7473-7485. [PMID: 31025567 PMCID: PMC6953484 DOI: 10.1021/jacs.9b02117] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A growing and useful class of alkene coupling reactions involve hydrogen atom transfer (HAT) from a metal-hydride species to an alkene to form a free radical, which is responsible for subsequent bond formation. Here, we use a combination of experimental and computational investigations to map out the mechanistic details of iron-catalyzed reductive alkene cross-coupling, an important representative of the HAT alkene reactions. We are able to explain several observations that were previously mysterious. First, the rate-limiting step in the catalytic cycle is the formation of the reactive Fe-H intermediate, elucidating the importance of the choice of reductant. Second, the success of the catalytic system is attributable to the exceptionally weak (17 kcal/mol) Fe-H bond, which performs irreversible HAT to alkenes in contrast to previous studies on isolable hydride complexes where this addition was reversible. Third, the organic radical intermediates can reversibly form organometallic species, which helps to protect the free radicals from side reactions. Fourth, the previously accepted quenching of the postcoupling radical through stepwise electron transfer/proton transfer is not as favorable as alternative mechanisms. We find that there are two feasible pathways. One uses concerted proton-coupled electron transfer (PCET) from an iron(II) ethanol complex, which is facilitated because the O-H bond dissociation free energy is lowered by 30 kcal/mol upon metal binding. In an alternative pathway, an O-bound enolate-iron(III) complex undergoes proton shuttling from an iron-bound alcohol. These kinetic, spectroscopic, and computational studies identify key organometallic species and PCET steps that control selectivity and reactivity in metal-catalyzed HAT alkene coupling, and create a firm basis for elucidation of mechanisms in the growing class of HAT alkene cross-coupling reactions.
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Affiliation(s)
- Dongyoung Kim
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - S. M. Wahidur Rahaman
- LCC-CNRS, Université de Toulouse, INPT, 205 Route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Rinaldo Poli
- LCC-CNRS, Université de Toulouse, INPT, 205 Route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France
| | - Patrick L. Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
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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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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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