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Ma P, Svatunek D, Zhu Z, Boger DL, Duan XH, Houk KN. Computational Studies of Reactions of 1,2,4,5-Tetrazines with Enamines in MeOH and HFIP. J Am Chem Soc 2024; 146:18706-18713. [PMID: 38941192 DOI: 10.1021/jacs.4c06067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/30/2024]
Abstract
The reaction between 1,2,4,5-tetrazines and alkenes in polar solvents proceeds through a Diels-Alder cycloaddition along the C-C axis (C3/C6 cycloaddition) of the tetrazine, followed by dinitrogen loss. By contrast, the reactions of 1,2,4,5-tetrazines with enamines in hexafluoroisopropanol (HFIP) give 1,2,4-triazine products stemming from a formal Diels-Alder addition across the N-N axis (N1/N4 cycloaddition). We explored the mechanism of this interesting solvent effect through DFT calculations in detail and revealed a novel reaction pathway characterized by C-N bond formation, deprotonation, and a 3,3-sigmatropic rearrangement. The participation of an HFIP molecule was found to be crucial to the N1/N4 selectivity over C3/C6 due to the more favored initial C-N bond formation than C-C bond formation.
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Affiliation(s)
- Pengchen Ma
- Department of Chemistry, School of Chemistry, Xi'an Key Laboratory of Sustainable Energy Material Chemistry and Engineering Research Center of Energy Storage Materials and Devices, Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Dennis Svatunek
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
- Institute of Applied Synthetic Chemistry, TU Wien, 1060 Vienna, Austria
| | - Zixi Zhu
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Dale L Boger
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Xin-Hua Duan
- Department of Chemistry, School of Chemistry, Xi'an Key Laboratory of Sustainable Energy Material Chemistry and Engineering Research Center of Energy Storage Materials and Devices, Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
| | - K N Houk
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
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2
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Hu X, Zhao X, Lv X, Wu YB, Bu Y, Lu G. Ab Initio Metadynamics Simulations of Hexafluoroisopropanol Solvent Effects: Synergistic Role of Solvent H-Bonding Networks and Solvent-Solute C-H/π Interactions. Chemistry 2023; 29:e202203879. [PMID: 36575142 DOI: 10.1002/chem.202203879] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2022] [Accepted: 12/27/2022] [Indexed: 12/29/2022]
Abstract
The solvent effects in Friedel-Crafts cycloalkylation of epoxides and Cope rearrangement of aldimines were investigated by using ab initio molecular dynamics simulations. Explicit molecular treatments were applied for both reactants and solvents. The reaction mechanisms were elucidated via free energy calculations based on metadynamics simulations. The results reveal that both reactions proceed in a concerted fashion. Key solvent-substrate interactions are identified from the structures of transition states with explicit solvent molecules. The remarkable promotion effect of hexafluoroisopropanol solvent is ascribed to the synergistic effect of H-bonding networks and C-H/π interactions with substrates.
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Affiliation(s)
- Xinmin Hu
- School of Chemistry and Chemical Engineering, Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University, Jinan, Shandong, 250100, P. R. China
| | - Xia Zhao
- School of Chemistry and Chemical Engineering, Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University, Jinan, Shandong, 250100, P. R. China
| | - Xiangying Lv
- School of Chemistry and Chemical Engineering, Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University, Jinan, Shandong, 250100, P. R. China
| | - Yan-Bo Wu
- Key Lab for Materials of Energy Conversion and Storage of Shanxi Province, and Key Lab of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Molecular Science, Shanxi University, Taiyuan, Shanxi, 030006, P. R. China
| | - Yuxiang Bu
- School of Chemistry and Chemical Engineering, Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University, Jinan, Shandong, 250100, P. R. China
| | - Gang Lu
- School of Chemistry and Chemical Engineering, Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University, Jinan, Shandong, 250100, P. R. China
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3
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Zhu Z, Boger DL. Acyclic and Heterocyclic Azadiene Diels-Alder Reactions Promoted by Perfluoroalcohol Solvent Hydrogen Bonding: Comprehensive Examination of Scope. J Org Chem 2022; 87:14657-14672. [PMID: 36239452 PMCID: PMC9637783 DOI: 10.1021/acs.joc.2c02000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Herein, the first use of perfluoroalcohol H-bonding in accelerating acyclic azadiene inverse electron demand cycloaddition reactions is described, and its use in the promotion of heterocyclic azadiene cycloaddition reactions is generalized through examination of a complete range of azadienes. The scope of dienophiles was comprehensively explored; relative reactivity trends and solvent compatibilities were established with respect to the dienophile as well as azadiene; H-bonding solvent effects that lead to rate enhancements, yield improvements, and their impact on regioselectivity and mode of cycloaddition are defined; new viable diene/dienophile reaction partners in the cycloaddition reactions are disclosed; and key comparison rate constants are reported. The perfluoroalcohol effectiveness at accelerating an inverse electron demand Diels-Alder cycloaddition is directly correlated with its H-bond potential (pKa). Not only are the reactions of electron-rich dienophiles accelerated but those of strained and even unactivated alkenes and alkynes are improved, including representative bioorthogonal click reactions.
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Affiliation(s)
- Zixi Zhu
- Department of Chemistry and the Skaggs Institute for Chemical-Biology, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Dale L Boger
- Department of Chemistry and the Skaggs Institute for Chemical-Biology, The Scripps Research Institute, La Jolla, California 92037, United States
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4
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Fatykhov RF, Khalymbadzha IA, Sharapov AD, Potapova AP, Mochulskaya NN, Tsmokalyuk AN, Ivoilova AV, Mozharovskaia PN, Santra S, Chupakhin ON. MnO 2-Mediated Oxidative Cyclization of "Formal" Schiff's Bases: Easy Access to Diverse Naphthofuro-Annulated Triazines. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27207105. [PMID: 36296698 PMCID: PMC9611995 DOI: 10.3390/molecules27207105] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/02/2022] [Revised: 10/12/2022] [Accepted: 10/13/2022] [Indexed: 11/16/2022]
Abstract
A different type of MnO2-induced oxidative cyclization of dihydrotriazines has been developed. These dihydrotriazines are considered as a "formal" Schiff's base. This method provided easy access to naphthofuro-fused triazine via the C-C/C-O oxidative coupling reaction. The reaction sequence comprised the nucleophilic addition of 2-naphthol or phenol to 1,2,4-triazine, followed by oxidative cyclization. The scope and limitations of this novel coupling reaction have been investigated. Further application of the synthesized compound has been demonstrated by synthesizing carbazole-substituted benzofuro-fused triazines. The scalability of the reaction was demonstrated at a 40 mmol load. The mechanistic study strongly suggests that this reaction proceeds through the formation of an O-coordinated manganese complex.
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Affiliation(s)
- Ramil F. Fatykhov
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
| | - Igor A. Khalymbadzha
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
- Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 22 S. Kovalevskaya Str., 620990 Ekaterinburg, Russia
| | - Ainur D. Sharapov
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
| | - Anastasia P. Potapova
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
| | - Nataliya N. Mochulskaya
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
| | - Anton N. Tsmokalyuk
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
| | - Alexandra V. Ivoilova
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
| | - Polina N. Mozharovskaia
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
| | - Sougata Santra
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
- Correspondence:
| | - Oleg N. Chupakhin
- Department of Organic and Biomolecular Chemistry, Chemical Engineering Institute, Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia
- Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 22 S. Kovalevskaya Str., 620990 Ekaterinburg, Russia
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Shankar M, Kalyani A, Anitha M, Siva Reddy A, Swamy KCK. Divergent Reactivity of Phosphorylated and Related Allenes: [4 + 2] Cycloaddition with 3,6-Diphenyltetrazine, Self-Addition Leading to Dimers and [Pd]-Complex Formation. J Org Chem 2022; 87:13683-13697. [PMID: 36197101 DOI: 10.1021/acs.joc.2c01337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phosphorus-based naphthalenes are formed by self-dimerization-cum-cyclization of α-aryl allenylphosphonates or allenylphosphine oxides using catalytic Pd(OAc)2in the presence of PPh3 and Et3N . This reaction involves [4 + 2]-cycloaddition with the (β,γ) double bond of one allene as the dienophile; the double bonds at the α-aryl-(β',γ') group and (α,β)-carbons of the second allene act as the diene part. A subsequent proton shift also takes place. Upon treating allenylphosphine oxides with Pd(OAc)2 [stoichiometry 2:1] in the presence of PPh3/Ag2CO3, a [Pd]-complex is isolated and structurally characterized. This complex can be used as a catalyst for C-C bond-forming reactions of phosphorus-based allenes with 2-iodophenol. Densely substituted 3,6-diphenylpyridazines are conveniently obtained in excellent yields by a thermally induced regioselective Inverse Electron Demand Diels-Alder (IEDDA) reaction of allenes with 3,6-diphenyltetrazine, followed by a [1,3]-H shift.
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Affiliation(s)
- Mallepalli Shankar
- School of Chemistry, University of Hyderabad, Hyderabad 500046, Telangana, India
| | - Adula Kalyani
- School of Chemistry, University of Hyderabad, Hyderabad 500046, Telangana, India
| | - Mandala Anitha
- School of Chemistry, University of Hyderabad, Hyderabad 500046, Telangana, India
| | - Alla Siva Reddy
- School of Chemistry, University of Hyderabad, Hyderabad 500046, Telangana, India
| | - K C Kumara Swamy
- School of Chemistry, University of Hyderabad, Hyderabad 500046, Telangana, India
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Bystrov DM, Pivkina AN, Fershtat LL. An Alliance of Polynitrogen Heterocycles: Novel Energetic Tetrazinedioxide-Hydroxytetrazole-Based Materials. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27185891. [PMID: 36144627 PMCID: PMC9505947 DOI: 10.3390/molecules27185891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 09/02/2022] [Accepted: 09/08/2022] [Indexed: 12/05/2022]
Abstract
Energetic materials constitute one of the most important subtypes of functional materials used for various applications. A promising approach for the construction of novel thermally stable high-energy materials is based on an assembly of polynitrogen biheterocyclic scaffolds. Herein, we report on the design and synthesis of a new series of high-nitrogen energetic salts comprising the C-C linked 6-aminotetrazinedioxide and hydroxytetrazole frameworks. Synthesized materials were thoroughly characterized by IR and multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction and differential scanning calorimetry. As a result of a vast amount of the formed intra- and intermolecular hydrogen bonds, prepared ammonium and amino-1,2,4-triazolium salts are thermally stable and have good densities of 1.75–1.78 g·cm−3. All synthesized compounds show high detonation performance, reaching that of benchmark RDX. At the same time, as compared to RDX, investigated salts are less friction sensitive due to the formed net of hydrogen bonds. Overall, reported functional materials represent a novel perspective subclass of secondary explosives and unveil further opportunities for an assembly of biheterocyclic next-generation energetic materials.
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Affiliation(s)
- Dmitry M. Bystrov
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences 47 Leninsky Prosp., 119991 Moscow, Russia
| | - Alla N. Pivkina
- N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 3 Kosygin Str., 119991 Moscow, Russia
| | - Leonid L. Fershtat
- N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences 47 Leninsky Prosp., 119991 Moscow, Russia
- Correspondence:
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7
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Fershtat LL. Recent advances in the synthesis and performance of 1,2,4,5-tetrazine-based energetic materials. FIREPHYSCHEM 2022. [DOI: 10.1016/j.fpc.2022.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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8
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Motiwala HF, Armaly AM, Cacioppo JG, Coombs TC, Koehn KRK, Norwood VM, Aubé J. HFIP in Organic Synthesis. Chem Rev 2022; 122:12544-12747. [PMID: 35848353 DOI: 10.1021/acs.chemrev.1c00749] [Citation(s) in RCA: 124] [Impact Index Per Article: 62.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.
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Affiliation(s)
- Hashim F Motiwala
- Divison of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 United States
| | - Ahlam M Armaly
- Divison of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 United States
| | - Jackson G Cacioppo
- Divison of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 United States
| | - Thomas C Coombs
- Department of Chemistry, University of North Carolina Wilmington, Wilmington, North Carolina 28403 United States
| | - Kimberly R K Koehn
- Divison of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 United States
| | - Verrill M Norwood
- Divison of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 United States
| | - Jeffrey Aubé
- Divison of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 United States
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9
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Galeta J, Šlachtová V, Dračínský M, Vrabel M. Regio- and Diastereoselective 1,3-Dipolar Cycloadditions of 1,2,4-Triazin-1-ium Ylides: a Straightforward Synthetic Route to Polysubstituted Pyrrolo[2,1- f][1,2,4]triazines. ACS OMEGA 2022; 7:21233-21238. [PMID: 35755338 PMCID: PMC9219532 DOI: 10.1021/acsomega.2c02276] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Accepted: 06/01/2022] [Indexed: 06/15/2023]
Abstract
A synthetic strategy to pyrrolo[2,1-f][1,2,4]triazines is reported. We show that various synthetically easily accessible 1,2,4-triazines can be efficiently alkylated under mild conditions to provide the corresponding 1-alkyl-1,2,4-triazinium salts. These bench-stable salts serve as precursors to triazinium ylides, which react in 1,3-dipolar cycloadditions with electron-poor dipolarophiles to yield polysubstituted pyrrolotriazines in a single step.
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10
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Zhu Z, Boger DL. N1/N4 1,4-Cycloaddition of 1,2,4,5-Tetrazines with Enamines Promoted by the Lewis Acid ZnCl 2. J Org Chem 2022; 87:6288-6301. [PMID: 35417656 PMCID: PMC9081262 DOI: 10.1021/acs.joc.2c00543] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The second example of selective N1/N4 1,4-cycloaddition (vs C3/C6 1,4-cycloaddition) of 1,2,4,5-tetrazines with preformed or in situ generated enamines now promoted by the Lewis acid ZnCl2 and with an expanded scope is described. The reaction constitutes a formal [4 + 2] cycloaddition across two nitrogen atoms (N1/N4 vs C3/C6) of a 1,2,4,5-tetrazine followed by retro [4 + 2] cycloaddition loss of a nitrile and aromatization to provide 1,2,4-triazines. Optimization of reaction parameters, simplification of its implementation through in situ enamine generation from ketones, definition of the enamine reaction scope for 3,6-bis(thiomethyl)-1,2,4,5-tetrazine, exploration of the 1,2,4,5-tetrazine scope, and representative applications of the product 1,2,4-triazines are detailed. The work establishes and further extends a powerful method for efficient one-step regioselective synthesis of 1,2,4-triazines under mild reaction conditions directly now from easily accessible ketones. It extends the substrate scope of a solvent (hexafluoroisopropanol) hydrogen bonding-promoted reaction that we recently reported with aryl-conjugated enamines, permitting the use of simple ketone-derived enamines and expanding the generality of the remarkable reaction. The reaction is regioselective with respect to the site of reaction with unsymmetrical ketones and provides exclusively a single 1,2,4-triazine regioisomer consistent with our previously established stepwise mechanism of formal N1/N4 1,4-cycloaddition, overcoming the challenges observed in conventional approaches to 1,2,4-triazines.
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Affiliation(s)
- Zixi Zhu
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, California 92037, United States
| | - Dale L Boger
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, California 92037, United States
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11
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Xie R, Zhao Z, Zhao Y, Li R, Yao J, Miao M. Synthesis of Trisubstituted Furans via Copper(I)-Catalyzed Strain-Driving Cycloisomerization/Annulative Fragmentation. Org Lett 2022; 24:2220-2225. [DOI: 10.1021/acs.orglett.2c00578] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ruyu Xie
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, P. R. China
| | - Zhiqiang Zhao
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, P. R. China
| | - Yongxing Zhao
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, P. R. China
| | - Rui Li
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, P. R. China
| | - Jinzhong Yao
- College of Biological, Chemical Sciences and Engineering, Jiaxing University, Jiaxing 314001, People’s Republic of China
| | - Maozhong Miao
- Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, P. R. China
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12
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Tian FX, Qu J. Studies on the Origin of the Stabilizing Effects of Fluorinated Alcohols and Weakly Coordinated Fluorine-Containing Anions on Cationic Reaction Intermediates. J Org Chem 2022; 87:1814-1829. [PMID: 35020378 DOI: 10.1021/acs.joc.1c02361] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Many synthetic methods that use fluorinated alcohols as solvents have been reported, and the fluorinated alcohols have been found to be crucial to the success of these methods. In addition, there have been reports indicating that adding a weakly coordinated fluorine-containing anion, such as BF4-, PF6-, or SbF6-, to fluorinated alcohols can improve yields. The boosting effect of fluorinated alcohols is attributed mainly to hydrogen bond activation. A few studies have suggested that the very polar fluorinated alcohols can stabilize cationic reaction intermediates. However, how they do so and why weakly coordinated fluorine-containing anions improve yields have not been studied in depth. Here, we used quaternary ammonium cations, a quaternary phosphonium cation, and a triaryl-substituted carbocation as models for short-lived cationic intermediates and studied the possible interactions of these cations with fluorinated alcohols and BF4-, PF6-, or SbF6-. On the basis of the results, we propose that the C-F dipoles of fluorinated alcohols and the E-F dipoles (where E is B, P, or Sb) of weakly coordinated fluorine-containing anions stabilized these cations by intermolecular charge-dipole interactions. We deduced that in the same fashion the C-F and E-F dipoles can thermodynamically stabilize cationic reaction intermediates.
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Affiliation(s)
- Feng-Xian Tian
- The State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China
| | - Jin Qu
- The State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China
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13
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Zhang FG, Chen Z, Tang X, Ma JA. Triazines: Syntheses and Inverse Electron-demand Diels-Alder Reactions. Chem Rev 2021; 121:14555-14593. [PMID: 34586777 DOI: 10.1021/acs.chemrev.1c00611] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Triazines are an important class of six-membered aromatic heterocycles possessing three nitrogen atoms, resulting in three types of regio-isomers: 1,2,4-triazines (a-triazines), 1,2,3-triazines (v-triazines), and 1,3,5-triazines (s-triazines). Notably, the application of triazines as cyclic aza-dienes in inverse electron-demand Diels-Alder (IEDDA) cycloaddition reactions has been established as a unique and powerful method in N-heterocycle synthesis, natural product preparation, and bioorthogonal chemistry. In this review, we comprehensively summarize the advances in the construction of these triazines via annulation and ring-expansion reactions, especially emphasizing recent developments and challenges. The synthetic transformations of triazines are focused on IEDDA cycloaddition reactions, which have allowed access to a wide scope of heterocycles, including pyridines, carbolines, azepines, pyridazines, pyrazines, and pyrimidines. The utilization of triazine IEDDA reactions as key steps in natural product synthesis is also discussed. More importantly, a particular attention is paid on the bioorthogonal application of triazines in fast click ligation with various strained alkenes and alkynes, which opens a new opportunity for studying biomolecules in chemical biology.
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Affiliation(s)
- Fa-Guang Zhang
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for Synthetic Biology (Ministry of Education), and Tianjin Collaborative Innovation Center of Chemical Science & Engineering, Tianjin University, Tianjin 300072, P. R. China.,Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, P. R. China
| | - Zhen Chen
- College of Chemical Engineering, Jiangsu Provincial Key Lab for the Chemistry and Utilization of Agro-Forest Biomass, Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Jiangsu Key Lab of Biomass-Based Green Fuels and Chemicals, Nanjing Forestry University, Nanjing, Jiangsu 210037, P. R. China
| | - Xiaodong Tang
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for Synthetic Biology (Ministry of Education), and Tianjin Collaborative Innovation Center of Chemical Science & Engineering, Tianjin University, Tianjin 300072, P. R. China.,Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, P. R. China
| | - Jun-An Ma
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Frontiers Science Center for Synthetic Biology (Ministry of Education), and Tianjin Collaborative Innovation Center of Chemical Science & Engineering, Tianjin University, Tianjin 300072, P. R. China.,Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, P. R. China
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14
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Quiñones RE, Wu ZC, Boger DL. Reaction Scope of Methyl 1,2,3-Triazine-5-carboxylate with Amidines and the Impact of C4/C6 Substitution. J Org Chem 2021; 86:13465-13474. [PMID: 34499494 DOI: 10.1021/acs.joc.1c01553] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A comprehensive study of the reaction scope of methyl 1,2,3-triazine-5-carboxylate (3a) with alkyl and aryl amidines is disclosed, reacting at room temperature at remarkable rates (<5 min, 0.1 M in CH3CN) nearly 10000-fold faster than that of unsubstituted 1,2,3-triazine and providing the product pyrimidines in high yields. C4 Methyl substitution of the 1,2,3-triazine (3b) had little effect on the rate of the reaction, whereas C4/C6 dimethyl substitution (3c) slowed the room-temperature reaction (<24 h, 0.25 M) but displayed an unaltered scope, providing the product pyrimidines in similarly high yields. Measured second-order rate constants of the reaction of 3a-c, the corresponding nitriles 3e and 3f, and 1,2,3-triazine itself (3d) with benzamidine and substituted derivatives quantitated the remarkable reactivity of 3a and 3e, verified the inverse electron demand nature of the reaction (Hammett ρ = -1.50 for substituted amidines, ρ = +7.9 for 5-substituted 1,2,3-triazine), and provided a quantitative measure of the impact of 4-methyl and 4,6-dimethyl substitution on the reactivity of the methyl 1,2,3-triazine-5-carboxylate and 5-cyano-1,2,3-triazine core heterocycles.
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Schnell SD, González JA, Sklyaruk J, Linden A, Gademann K. Boron Trifluoride-Mediated Cycloaddition of 3-Bromotetrazine and Silyl Enol Ethers: Synthesis of 3-Bromo-pyridazines. J Org Chem 2021; 86:12008-12023. [PMID: 34342995 DOI: 10.1021/acs.joc.1c01384] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Pyridazines are important scaffolds for medicinal chemistry or crop protection agents, yet the selective preparation of 3-bromo-pyridazines with high regiocontrol remains difficult. We achieved the Lewis acid-mediated inverse electron demand Diels-Alder reaction between 3-monosubstituted s-tetrazine and silyl enol ethers and obtained functionalized pyridazines. In the case of 1-monosubstituted silyl enol ethers, exclusive regioselectivity was observed. Downstream functionalization of the resulting 3-bromo-pyridazines was demonstrated utilizing several cross-coupling protocols to synthesize 3,4-disubstituted pyridazines with excellent control over the substitution pattern.
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Affiliation(s)
- Simon D Schnell
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Jorge A González
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Jan Sklyaruk
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Anthony Linden
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Karl Gademann
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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Schnierle M, Leimkühler M, Ringenberg MR. [(η 6- p-Cymene)[3-(pyrid-2-yl)-1,2,4,5-tetrazine]chlororuthenium(II)] +, Redox Noninnocence and Dienophile Addition to Coordinated Tetrazine. Inorg Chem 2021; 60:6367-6374. [PMID: 33856810 DOI: 10.1021/acs.inorgchem.1c00094] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bidentate ligand 3-(pyrid-2-yl)-1,2,4,5-tetrazine (TzPy) coordinated in the complex [CyRuCl(TzPy)]PF6 ([1]+; Cy = η6-p-cymene) shows noninnocent behavior and can be modified through the addition of dienophiles, vinylferrocene (ViFc) or ethynylferrocene (EthFc). The kinetics and transition-state thermodynamic analysis of the reaction of [1]+ + ViFc found ΔG⧧(298 K) = 67 kJ mol-1, while that of [1]+ + EthFc was ΔG⧧(298 K) = 83 kJ mol-1. The room temperature second-order rate of [1]+ + EthFc, k2 = 1.51(4) × 10-2 M-1 s-1, was 3 orders of magnitude faster than that of EthFc + TzPy, k2 = 1.05(15) × 10-4 M-1 s-1. The [1H2Fc]+ complex was converted to [1Fc]+ by oxidation with oxygen and 3,5-di-tert-butyl-o-quinone, and the molecular structure of [1Fc]+ was determined by single-crystal X-ray diffraction. The title complex [1]+ showed a quasi-reversible reduction in the cyclic voltammogram, and the electrochemical reduction mechanism was determined by UV-vis spectroelectrochemistry (SEC) experiments, as well as supported by density functional theory (DFT) calculations. The dihydropyridazine [1H2Fc]+ and pyridazine [1Fc]+ states of the ligand showed ligand noninnocence similar to that of the parent tetrazine but at a cathodically shifted potential. The dihydropyridazine [1H2Fc]+ showed a mixture of several products; however, upon oxidation, only a single product, [1Fc]+, was formed from the endo addition of the dienophile to [1]+. The electrochemical mechanism of [1Fc]+ was also studied by cyclic voltammetry and UV-vis SEC experiments, as well as supported by DFT calculations.
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Affiliation(s)
- Marc Schnierle
- Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Marie Leimkühler
- Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Mark R Ringenberg
- Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
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Schnell SD, Schilling M, Sklyaruk J, Linden A, Luber S, Gademann K. Nucleophilic Attack on Nitrogen in Tetrazines by Silyl-Enol Ethers. Org Lett 2021; 23:2426-2430. [PMID: 33703907 DOI: 10.1021/acs.orglett.0c04113] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The nucleophilic addition of silyl-enol ethers to nitrogen in 3-monosubstituted s-tetrazines mediated by BF3 is reported. The preference for this azaphilic addition over the usually observed inverse electron demand Diels-Alder reactions was evaluated theoretically and corroborated by experiments. The substrate dependency of this unusual reaction was rationalized by determination of the activation barriers and on the basis of the activation strain model by employing density functional theory.
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Affiliation(s)
- Simon D Schnell
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Mauro Schilling
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Jan Sklyaruk
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Anthony Linden
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Sandra Luber
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Karl Gademann
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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