1
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Zhu Q, Chen S, Chen D, Lin L, Xiao K, Zhao L, Solà M, Zhu J. The application of aromaticity and antiaromaticity to reaction mechanisms. FUNDAMENTAL RESEARCH 2023; 3:926-938. [PMID: 38933008 PMCID: PMC11197727 DOI: 10.1016/j.fmre.2023.04.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2023] [Revised: 03/31/2023] [Accepted: 04/24/2023] [Indexed: 06/28/2024] Open
Abstract
Aromaticity, in general, can promote a given reaction by stabilizing a transition state or a product via a mobility of π electrons in a cyclic structure. Similarly, such a promotion could be also achieved by destabilizing an antiaromatic reactant. However, both aromaticity and transition states cannot be directly measured in experiment. Thus, computational chemistry has been becoming a key tool to understand the aromaticity-driven reaction mechanisms. In this review, we will analyze the relationship between aromaticity and reaction mechanism to highlight the importance of density functional theory calculations and present it according to an approach via either aromatizing a transition state/product or destabilizing a reactant by antiaromaticity. Specifically, we will start with a particularly challenging example of dinitrogen activation followed by other small-molecule activation, C-F bond activation, rearrangement, as well as metathesis reactions. In addition, antiaromaticity-promoted dihydrogen activation, CO2 capture, and oxygen reduction reactions will be also briefly discussed. Finally, caution must be cast as the magnitude of the aromaticity in the transition states is not particularly high in most cases. Thus, a proof of an adequate electron delocalization rather than a complete ring current is recommended to support the relatively weak aromaticity in these transition states.
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Affiliation(s)
- Qin Zhu
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
- Key Laboratory for Organic Electronics & Information Displays (KLOEID) and Institute of Advanced Materials (IAM), SICAM, Nanjing University of Posts & Telecommunications, Nanjing 210023, China
| | - Shuwen Chen
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Dandan Chen
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Lu Lin
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Kui Xiao
- Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Liang Zhao
- Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Miquel Solà
- Institute of Computational Chemistry and Catalysis and Department of Chemistry, University of Girona, C/ M. Aurèlia Capmany, 69, 17003 Girona, Catalonia, Spain
| | - Jun Zhu
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
- School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen 518172, China
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2
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Levandowski BJ, Abularrage NS, Graham BJ, Raines RT. Computational study of an oxetane 4 H-pyrazole as a Diels-Alder diene. Tetrahedron Lett 2023; 130:154768. [PMID: 37860707 PMCID: PMC10584014 DOI: 10.1016/j.tetlet.2023.154768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2023]
Abstract
We combine the effects of spirocyclization and hyperconjugation to increase the Diels-Alder reactivity of the 4H-pyrazole scaffold. A density functional theory (DFT) investigation predicts that 4H-pyrazoles containing an oxetane functionality at the saturated center are extremely reactive despite having a relatively high-lying lowest unoccupied molecular orbital (LUMO) energy.
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Affiliation(s)
- Brian J. Levandowski
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA
| | - Nile S. Abularrage
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA
| | - Brian J. Graham
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA
| | - Ronald T. Raines
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA
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3
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Svatunek D, Chojnacki K, Deb T, Eckvahl H, Houk KN, Franzini RM. Orthogonal Inverse-Electron-Demand Cycloaddition Reactions Controlled by Frontier Molecular Orbital Interactions. Org Lett 2023; 25:6340-6345. [PMID: 37591496 PMCID: PMC10476241 DOI: 10.1021/acs.orglett.3c02265] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Indexed: 08/19/2023]
Abstract
Chemoselective pairs of bioorthogonal reactants enable the simultaneous labeling of several biomolecules. Here, we access orthogonal click reactions by exploiting differences in frontier molecular orbital interaction energies in transition states. We establish that five-membered cyclic dienes are inert to isonitriles but readily react with strained alkynes, while tetrazines with bulky substituents readily react with isonitriles. Strained alkynes show an opposite reactivity pattern. The approach was demonstrated by orthogonally labeling two proteins with different fluorophores.
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Affiliation(s)
- 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
| | - Konrad Chojnacki
- Department
of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Titas Deb
- Department
of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Hannah Eckvahl
- Department
of Chemistry and Biochemistry, University
of California, Los Angeles, Los Angeles, California 90095, United States
| | - K. N. Houk
- Department
of Chemistry and Biochemistry, University
of California, Los Angeles, Los Angeles, California 90095, United States
| | - Raphael M. Franzini
- Department
of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
- Huntsman
Cancer Institute, Salt Lake City, Utah 84112, United States
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4
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Abularrage NS, Levandowski BJ, Giancola JB, Graham BJ, Raines RT. Bioorthogonal 4 H-pyrazole "click" reagents. Chem Commun (Camb) 2023; 59:4451-4454. [PMID: 36987784 PMCID: PMC10088812 DOI: 10.1039/d3cc00112a] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Accepted: 03/07/2023] [Indexed: 03/30/2023]
Abstract
4H-Pyrazoles are emerging as useful click reagents. Fluorinating the saturated center enables 4H-pyrazoles to react rapidly as Diels-Alder dienes without a catalyst but compromises the stability of these dienes under physiological conditions. To identify more stable 4H-pyrazoles for bioorthogonal chemistry applications, we investigated the Diels-Alder reactivity and biological stability of three 4-oxo-substituted 4H-pyrazoles. We found that these dienes undergo rapid Diels-Alder reactions with endo-bicyclo[6.1.0]non-4-yne (BCN) while being much more stable to biological nucleophiles than their fluorinated counterparts. We attribute the rapid Diels-Alder reactivity of the optimal oxygen-substituted pyrazole to a combination of antiaromaticity, predistortion, and spirocyclization. Their reactivity and stability suggest that 4-oxo-4H-pyrazoles can be useful bioorthogonal reagents.
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Affiliation(s)
- Nile S Abularrage
- Department of Chemistry, Massachusetts institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
| | - Brian J Levandowski
- Department of Chemistry, Massachusetts institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
| | - JoLynn B Giancola
- Department of Chemistry, Massachusetts institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
| | - Brian J Graham
- Department of Chemistry, Massachusetts institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
| | - Ronald T Raines
- Department of Chemistry, Massachusetts institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
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5
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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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6
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Ito S, Ishii Y, Kuwabara T. Inorganic salt-assisted assembly of anionic π-conjugated rings enabling 7Li NMR-based evaluation of antiaromaticity. Dalton Trans 2022; 51:16397-16402. [DOI: 10.1039/d2dt02649j] [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 cluster composed of three dilithium dibenzosilepinides and two Li2O molecules showed downfield shifted 7Li{1H} NMR signals (δ = 6.3, 4.4) due to the paratropic ring currents of the dianionic dibenzosilepins.
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Affiliation(s)
- Shotaro Ito
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, Tokyo, 112-8551, Japan
| | - Youichi Ishii
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, Tokyo, 112-8551, Japan
| | - Takuya Kuwabara
- Department of Chemistry and Biochemistry, Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1, Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan
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7
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Yuan SP, Dou PH, Jia YQ, Zhao JQ, You Y, Wang ZH, Zhou MQ, Yuan WC. Catalytic asymmetric aromatizing inverse electron-demand [4+2] cycloaddition of 1-thioaurones and 1-azaaurones. Chem Commun (Camb) 2021; 58:553-556. [PMID: 34908046 DOI: 10.1039/d1cc06357j] [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
Using 1-thioaurones and 1-azaaurones as electron-deficient oxa-dienes, an organocatalytic asymmetric aromatizing inverse electron-demand [4+2] cycloaddition with γ-deconjugated butenolides and azlactones was developed. A wide range of optically active benzothiophene-fused δ-lactones and indole-fused δ-lactones were obtained with desirable outcomes (up to 94% yield, >99 : 1 dr and 99% ee).
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Affiliation(s)
- Shu-Pei Yuan
- National Engineering Research Center of Chiral Drugs, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China. .,Innovation Research Center of Chiral Drugs, Institute for Advanced Study, Chengdu University, Chengdu 610106, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Pei-Hao Dou
- National Engineering Research Center of Chiral Drugs, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China. .,Innovation Research Center of Chiral Drugs, Institute for Advanced Study, Chengdu University, Chengdu 610106, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yun-Qing Jia
- National Engineering Research Center of Chiral Drugs, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China. .,Innovation Research Center of Chiral Drugs, Institute for Advanced Study, Chengdu University, Chengdu 610106, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jian-Qiang Zhao
- Innovation Research Center of Chiral Drugs, Institute for Advanced Study, Chengdu University, Chengdu 610106, China
| | - Yong You
- Innovation Research Center of Chiral Drugs, Institute for Advanced Study, Chengdu University, Chengdu 610106, China
| | - Zhen-Hua Wang
- Innovation Research Center of Chiral Drugs, Institute for Advanced Study, Chengdu University, Chengdu 610106, China
| | - Ming-Qiang Zhou
- National Engineering Research Center of Chiral Drugs, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China.
| | - Wei-Cheng Yuan
- National Engineering Research Center of Chiral Drugs, Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China. .,Innovation Research Center of Chiral Drugs, Institute for Advanced Study, Chengdu University, Chengdu 610106, China
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8
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Ito S, Ishii Y, Ishimura K, Kuwabara T. A new strategy for hyperconjugative antiaromatic compounds utilizing negative charges: a dibenzo[ b, f]silepinyl dianion. Chem Commun (Camb) 2021; 57:11330-11333. [PMID: 34636825 DOI: 10.1039/d1cc04434f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Herein we propose a new strategy for hyperconjugative antiaromatic compounds utilizing negative charges and design the 5,5-diphenyldibenzo[b,f]silepinyl dianion (pseudo 16π-electron system) in which negative hyperconjugation occurs between the anionic π-cloud and the σ*(Si-Ph) orbital. Essentially, reduction of the dibenzo[b,f]silepin with lithium readily generated a dilithium salt of the dibenzosilepinyl dianion, and its hyperconjugative antiaromaticity has been evidenced by the upfield shifts of 1H NMR signals and theoretical calculations, including large NICSzz values and ACID plots.
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Affiliation(s)
- Shotaro Ito
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, Tokyo, 112-8551, Japan
| | - Youichi Ishii
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, Tokyo, 112-8551, Japan
| | - Kazuya Ishimura
- X-Ability, Co., Ltd., Ishiwata Building 3rd Floor, 4-1-5 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Takuya Kuwabara
- Department of Chemistry and Biochemistry, Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1, Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan.
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9
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Levandowski BJ, Abularrage NS, Raines RT. Geminal Repulsion Disrupts Diels-Alder Reactions of Geminally Substituted Cyclopentadienes and 4 H-Pyrazoles. Tetrahedron 2021; 91. [PMID: 34290459 DOI: 10.1016/j.tet.2021.132160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We have experimentally and computationally explored the sluggish Diels-Alder reactivities of the geminally substituted 5,5-dimethylcyclopentadiene and 5,5-dimethyl-2,3-diazacyclopentadiene (4,4-dimethyl-4H-pyrazole) scaffolds. We found that geminal dimethylation of 1,2,3,4-tetramethylcyclopentadiene to 1,2,3,4,5,5-hexamethylcyclopentadiene decreases the Diels-Alder reactivity towards maleimide by 954-fold. Quantum mechanical calculations revealed that the decreased Diels-Alder reactivities of gem-dimethyl substituted cyclopentadienes and 2,3-diazacyclopentadienes are not a consequence of unfavorable steric interactions between the diene and dienophile as reported previously, but a consequence of the increased repulsion within the gem-dimethyl group in the transition state. The findings have implications for the use of cyclopentadienes in "click" chemistry.
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Affiliation(s)
- Brian J Levandowski
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Nile S Abularrage
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Ronald T Raines
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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10
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Abstract
Cyclopentadiene is one of the most reactive dienes in normal electron-demand Diels-Alder reactions. The high reactivities and yields of cyclopentadiene cycloadditions make them ideal as click reactions. In this review, we discuss the history of the cyclopentadiene cycloaddition as well as applications of cyclopentadiene click reactions. Our emphasis is on experimental and theoretical studies on the reactivity and stability of cyclopentadiene and cyclopentadiene derivatives.
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Affiliation(s)
- Brian J. Levandowski
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Ronald T. Raines
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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11
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Deb T, Tu J, Franzini RM. Mechanisms and Substituent Effects of Metal-Free Bioorthogonal Reactions. Chem Rev 2021; 121:6850-6914. [DOI: 10.1021/acs.chemrev.0c01013] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Titas Deb
- Department of Medicinal Chemistry, University of Utah, 30 S 2000 E, Salt Lake City, Utah 84112, United States
| | - Julian Tu
- Department of Medicinal Chemistry, University of Utah, 30 S 2000 E, Salt Lake City, Utah 84112, United States
| | - Raphael M. Franzini
- Department of Medicinal Chemistry, University of Utah, 30 S 2000 E, Salt Lake City, Utah 84112, United States
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12
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Zhao Y, Zeng J, Zhu J. Tuning the hyperconjugative aromaticity in Au(III)-substituted indoliums. Dalton Trans 2021; 50:8096-8101. [PMID: 34018516 DOI: 10.1039/d1dt00599e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
As a fundamental concept in chemistry, aromaticity has been extended from traditional organics to organometallics. Similarly, hyperconjugative aromaticity (HCA) has also been developed from main group to transition metal systems through the hyperconjugation of the substituents. However, it remains unclear that how the oxidation state of transition metal in the substituents affects the HCA. Herein, we demonstrate via density functional theory calculations that HCA could disappear in indoliums when the Au(i) substituents are changed to the Au(iii) ones. By tuning the ligand or cis-trans isomerization, HCA could be regained or enhanced in indoliums containing Au(iii) substitutents.
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Affiliation(s)
- Yu Zhao
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
| | - Jie Zeng
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
| | - Jun Zhu
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
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13
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Karas LJ, Campbell AT, Alabugin IV, Wu JI. Antiaromaticity Gain Activates Tropone and Nonbenzenoid Aromatics as Normal-Electron-Demand Diels-Alder Dienes. Org Lett 2020; 22:7083-7087. [PMID: 32856925 PMCID: PMC8124018 DOI: 10.1021/acs.orglett.0c02343] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We propose a carbonyl umpolung strategy for activating tropone as a normal-electron-demand Diels-Alder diene. Tropone has low reactivity for Diels-Alder reactions because of its [4n+2] π-aromaticity. Conversion of the carbonyl group into a hydrazone ion (═N-NR-) reverses the polarity of the exocyclic double bond, increases the [4n] ring π-antiaromaticity, and raises the HOMO energy. Computed gas-phase activation free energies for a Diels-Alder reaction with maleimide suggest a billion-fold rate increase when the tropone C═O is replaced by ═N-NR- (R = H or SO2CH3). Other nonbenzenoid aromatics can be activated as normal-electron-demand Diels-Alder dienes in the same way.
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Affiliation(s)
- Lucas J Karas
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
| | - Adam T Campbell
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Igor V Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Judy I Wu
- Department of Chemistry, University of Houston, Houston, Texas 77204, United States
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14
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Adachi K, Meguro T, Sakata Y, Igawa K, Tomooka K, Hosoya T, Yoshida S. Selective strain-promoted azide-alkyne cycloadditions through transient protection of bicyclo[6.1.0]nonynes with silver or gold. Chem Commun (Camb) 2020; 56:9823-9826. [PMID: 32716445 DOI: 10.1039/d0cc04606j] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Complexation of bicyclo[6.1.0]nonynes with a cationic silver or gold salt results in protection from a click reaction with azides. The cycloalkyne protection using the silver or gold salt enables selective strain-promoted azide-alkyne cycloadditions of diynes keeping the bicyclo[6.1.0]nonyne moiety unreacted.
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Affiliation(s)
- Keisuke Adachi
- Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
| | - Tomohiro Meguro
- Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
| | - Yuki Sakata
- Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
| | - Kazunobu Igawa
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
| | - Katsuhiko Tomooka
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
| | - Takamitsu Hosoya
- Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
| | - Suguru Yoshida
- Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
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15
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Levandowski BJ, Abularrage NS, Raines RT. Differential Effects of Nitrogen Substitution in 5- and 6-Membered Aromatic Motifs. Chemistry 2020; 26:8862-8866. [PMID: 32166866 PMCID: PMC7374023 DOI: 10.1002/chem.202000825] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Indexed: 12/30/2022]
Abstract
The replacement of carbon with nitrogen can affect the aromaticity of organic rings. Nucleus-independent chemical shift (NICS) calculations at the center of the aromatic π-systems reveal that incorporating nitrogen into 5-membered heteroaromatic dienes has only a small influence on aromaticity. In contrast, each nitrogen incorporated into benzene results in a sequential and substantial loss of aromaticity. The contrasting effects of nitrogen substitution in 5-membered dienes and benzene are reflected in their Diels-Alder reactivities as dienes. 1,2-Diazine experiences a 1011 -fold increase in reactivity upon nitrogen substitution at the 4- and 5-positions, whereas a 5-membered heteroaromatic diene, furan, experiences a comparatively incidental 102 -fold increase in reactivity upon nitrogen substitution at the 3- and 4-positions.
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Affiliation(s)
- Brian J. Levandowski
- Dedicated to Rolf Huisgen in honor of his 100 birthday and contributions to cycloaddition chemistry
| | - Nile S. Abularrage
- Dedicated to Rolf Huisgen in honor of his 100 birthday and contributions to cycloaddition chemistry
| | - Ronald T. Raines
- Dedicated to Rolf Huisgen in honor of his 100 birthday and contributions to cycloaddition chemistry
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16
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Nguyen SS, Prescher JA. Developing bioorthogonal probes to span a spectrum of reactivities. Nat Rev Chem 2020; 4:476-489. [PMID: 34291176 DOI: 10.1038/s41570-020-0205-0] [Citation(s) in RCA: 96] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Bioorthogonal chemistries enable researchers to interrogate biomolecules in living systems. These reactions are highly selective and biocompatible and can be performed in many complex environments. However, like any organic transformation, there is no perfect bioorthogonal reaction. Choosing the "best fit" for a desired application is critical. Correspondingly, there must be a variety of chemistries-spanning a spectrum of rates and other features-to choose from. Over the past few years, significant strides have been made towards not only expanding the number of bioorthogonal chemistries, but also fine-tuning existing reactions for particular applications. In this Review, we highlight recent advances in bioorthogonal reaction development, focusing on how physical organic chemistry principles have guided probe design. The continued expansion of this toolset will provide more precisely tuned reagents for manipulating bonds in distinct environments.
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Affiliation(s)
- Sean S Nguyen
- Departments of Chemistry, University of California, Irvine, California 92697, United States
| | - Jennifer A Prescher
- Departments of Chemistry, University of California, Irvine, California 92697, United States.,Molecular Biology & Biochemistry, University of California, Irvine, California 92697, United States.,Pharmaceutical Sciences, University of California, Irvine, California 92697, United States
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Abularrage NS, Levandowski BJ, Raines RT. Synthesis and Diels-Alder Reactivity of 4-Fluoro-4-Methyl-4 H-Pyrazoles. Int J Mol Sci 2020; 21:ijms21113964. [PMID: 32486503 PMCID: PMC7312747 DOI: 10.3390/ijms21113964] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 05/22/2020] [Accepted: 05/24/2020] [Indexed: 02/01/2023] Open
Abstract
4H-Pyrazoles are emerging scaffolds for “click” chemistry. Late-stage fluorination with Selectfluor® is found to provide a reliable route to 4-fluoro-4-methyl-4H-pyrazoles. 4-Fluoro-4-methyl-3,5-diphenyl-4H-pyrazole (MFP) manifested 7-fold lower Diels–Alder reactivity than did 4,4-difluoro-3,5-diphenyl-4H-pyrazole (DFP), but higher stability in the presence of biological nucleophiles. Calculations indicate that a large decrease in the hyperconjugative antiaromaticity in MFP relative to DFP does not lead to a large loss in Diels–Alder reactivity because the ground-state structure of MFP avoids hyperconjugative antiaromaticity by distorting into an envelope-like conformation like that in the Diels–Alder transition state. This predistortion enhances the reactivity of MFP and offsets the decrease in reactivity from the diminished hyperconjugative antiaromaticity.
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