1
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Wang M, Rowshanpour R, Guan L, Ruskin J, Nguyen PM, Wang Y, Zhang QA, Liu R, Ling B, Woltornist R, Stephens AM, Prasad A, Dudding T, Lectka T, Pitts CR. Competition between C-C and C-H Bond Fluorination: A Continuum of Electron Transfer and Hydrogen Atom Transfer Mechanisms. J Am Chem Soc 2023; 145:22442-22455. [PMID: 37791901 DOI: 10.1021/jacs.3c06477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
In 2015, we reported a photochemical method for directed C-C bond cleavage/radical fluorination of relatively unstrained cyclic acetals using Selectfluor and catalytic 9-fluorenone. Herein, we provide a detailed mechanistic study of this reaction, during which it was discovered that the key electron transfer step proceeds through substrate oxidation from a Selectfluor-derived N-centered radical intermediate (rather than through initially suspected photoinduced electron transfer). This finding led to proof of concept for two new methodologies, demonstrating that unstrained C-C bond fluorination can also be achieved under chemical and electrochemical conditions. Moreover, as C-C and C-H bond fluorination reactions are both theoretically possible on 2-aryl-cycloalkanone acetals and would involve the same reactive intermediate, we studied the competition between single-electron transfer (SET) and apparent hydrogen-atom transfer (HAT) pathways in acetal fluorination reactions using density functional theory. Finally, these analyses were applied more broadly to other classes of C-H and C-C bond fluorination reactions developed over the past decade, addressing the feasibility of SET processes masquerading as HAT in C-H fluorination literature.
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Affiliation(s)
- Muyuan Wang
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Rozhin Rowshanpour
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way St. Catharines, Ontario L2S 3A1, Canada
| | - Liangyu Guan
- BayRay Innovation Center, Shenzhen Bay Laboratory, Shenzhen 51832, China
| | - Jonah Ruskin
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Phuong Minh Nguyen
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Yuang Wang
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Qinze Arthur Zhang
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Ran Liu
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Bill Ling
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Ryan Woltornist
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Alexander M Stephens
- Department of Chemistry, University of California Davis, 1 Shields Avenue, Davis, California 95616, United States
| | - Aarush Prasad
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Travis Dudding
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way St. Catharines, Ontario L2S 3A1, Canada
| | - Thomas Lectka
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Cody Ross Pitts
- Department of Chemistry, University of California Davis, 1 Shields Avenue, Davis, California 95616, United States
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2
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Yakubov S, Stockerl WJ, Tian X, Shahin A, Mandigma MJP, Gschwind RM, Barham JP. Benzoates as photosensitization catalysts and auxiliaries in efficient, practical, light-powered direct C(sp 3)-H fluorinations. Chem Sci 2022; 13:14041-14051. [PMID: 36540818 PMCID: PMC9728569 DOI: 10.1039/d2sc05735b] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Accepted: 10/28/2022] [Indexed: 12/14/2023] Open
Abstract
Of the methods for direct fluorination of unactivated C(sp3)-H bonds, photosensitization of SelectFluor is a promising approach. Although many substrates can be activated with photosensitizing catalysts, issues remain that hamper fluorination of complex molecules. Alcohol- or amine-containing functional groups are not tolerated, fluorination regioselectivity follows factors endogenous to the substrate and cannot be influenced by the catalyst, and reactions are highly air-sensitive. We report that benzoyl groups serve as highly efficient photosensitizers which, in combination with SelectFluor, enable visible light-powered direct fluorination of unactivated C(sp3)-H bonds. Compared to previous photosensitizer architectures, the benzoyls have versatility to function both (i) as a photosensitizing catalyst for simple substrate fluorinations and (ii) as photosensitizing auxiliaries for complex molecule fluorinations that are easily installed and removed without compromising yield. Our auxiliary approach (i) substantially decreases the reaction's induction period, (ii) enables C(sp3)-H fluorination of many substrates that fail under catalytic conditions, (iii) increases kinetic reproducibility, and (iv) promotes reactions to higher yields, in shorter times, on multigram scales, and even under air. Observations and mechanistic studies suggest an intimate 'assembly' of auxiliary and SelectFluor prior/after photoexcitation. The auxiliary allows other EnT photochemistry under air. Examples show how auxiliary placement proximally directs regioselectivity, where previous methods are substrate-directed.
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Affiliation(s)
- Shahboz Yakubov
- Fakultät für Chemie und Pharmazie, Universität Regensburg 93040 Regensburg Germany
| | - Willibald J Stockerl
- Fakultät für Chemie und Pharmazie, Universität Regensburg 93040 Regensburg Germany
| | - Xianhai Tian
- Fakultät für Chemie und Pharmazie, Universität Regensburg 93040 Regensburg Germany
| | - Ahmed Shahin
- Fakultät für Chemie und Pharmazie, Universität Regensburg 93040 Regensburg Germany
- Chemistry Department, Faculty of Science, Benha University 13518 Benha Egypt
| | - Mark John P Mandigma
- Fakultät für Chemie und Pharmazie, Universität Regensburg 93040 Regensburg Germany
| | - Ruth M Gschwind
- Fakultät für Chemie und Pharmazie, Universität Regensburg 93040 Regensburg Germany
| | - Joshua P Barham
- Fakultät für Chemie und Pharmazie, Universität Regensburg 93040 Regensburg Germany
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3
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Yakubov S, Barham JP. Photosensitized direct C-H fluorination and trifluoromethylation in organic synthesis. Beilstein J Org Chem 2020; 16:2151-2192. [PMID: 32952732 PMCID: PMC7476599 DOI: 10.3762/bjoc.16.183] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Accepted: 08/17/2020] [Indexed: 12/11/2022] Open
Abstract
The importance of fluorinated products in pharmaceutical and medicinal chemistry has necessitated the development of synthetic fluorination methods, of which direct C-H fluorination is among the most powerful. Despite the challenges and limitations associated with the direct fluorination of unactivated C-H bonds, appreciable advancements in manipulating the selectivity and reactivity have been made, especially via transition metal catalysis and photochemistry. Where transition metal catalysis provides one strategy for C-H bond activation, transition-metal-free photochemical C-H fluorination can provide a complementary selectivity via a radical mechanism that proceeds under milder conditions than thermal radical activation methods. One exciting development in C-F bond formation is the use of small-molecule photosensitizers, allowing the reactions i) to proceed under mild conditions, ii) to be user-friendly, iii) to be cost-effective and iv) to be more amenable to scalability than typical photoredox-catalyzed methods. In this review, we highlight photosensitized C-H fluorination as a recent strategy for the direct and remote activation of C-H (especially C(sp3)-H) bonds. To guide the readers, we present the developing mechanistic understandings of these reactions and exemplify concepts to assist the future planning of reactions.
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Affiliation(s)
- Shahboz Yakubov
- Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, 93040 Regensburg, Germany
| | - Joshua P Barham
- Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstraße 31, 93040 Regensburg, Germany
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4
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Ghorbani F, Harry SA, Capilato JN, Pitts CR, Joram J, Peters GN, Tovar JD, Smajlagic I, Siegler MA, Dudding T, Lectka T. Carbonyl-Directed Aliphatic Fluorination: A Special Type of Hydrogen Atom Transfer Beats Out Norrish II. J Am Chem Soc 2020; 142:14710-14724. [PMID: 32786786 DOI: 10.1021/jacs.0c07004] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Recently, our group reported that enone and ketone functional groups, upon photoexcitation, can direct site-selective sp3 C-H fluorination in terpenoid derivatives. How this transformation actually occurred remained mysterious, as a significant number of mechanistic possibilities came to mind. Herein, we report a comprehensive study describing the reaction mechanism through kinetic studies, isotope-labeling experiments, 19F NMR, electrochemical studies, synthetic probes, and computational experiments. To our surprise, the mechanism suggests intermolecular hydrogen atom transfer (HAT) chemistry is at play, rather than classical Norrish hydrogen atom abstraction as initially conceived. What is more, we discovered a unique role for photopromoters such as benzil and related compounds that necessitates their chemical transformation through fluorination in order to be effective. Our findings provide documentation of an unusual form of directed HAT and are of crucial importance for defining the necessary parameters for the development of future methods.
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Affiliation(s)
- Fereshte Ghorbani
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Stefan Andrew Harry
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Joseph N Capilato
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Cody Ross Pitts
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Jacob Joram
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Garvin N Peters
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - John D Tovar
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Ivor Smajlagic
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
| | - Maxime A Siegler
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Travis Dudding
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
| | - Thomas Lectka
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
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5
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Aguilar Troyano FJ, Merkens K, Gómez‐Suárez A. Selectfluor® Radical Dication (TEDA
2+.
) – A Versatile Species in Modern Synthetic Organic Chemistry. ASIAN J ORG CHEM 2020. [DOI: 10.1002/ajoc.202000196] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
| | - Kay Merkens
- Organic ChemistryBergische Universität Wuppertal Gaußstr. 20 42119 Wuppertal Germany
| | - Adrián Gómez‐Suárez
- Organic ChemistryBergische Universität Wuppertal Gaußstr. 20 42119 Wuppertal Germany
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6
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Diem Ferreira Xavier MC, Andia Sandagorda EM, Santos Neto JS, Schumacher RF, Silva MS. Synthesis of 3-selanylbenzo[ b]furans promoted by SelectFluor®. RSC Adv 2020; 10:13975-13983. [PMID: 35498450 PMCID: PMC9051628 DOI: 10.1039/d0ra01907k] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 03/30/2020] [Indexed: 11/21/2022] Open
Abstract
A simple and practical protocol for the synthesis of 3-selanyl-benzo[b]furans mediated by the SelectFluor® reagent was developed. This novel methodology provided a greener alternative to generate 3-substituted-benzo[b]furans via a metal-free procedure under mild conditions. The intramolecular cyclization reaction was carried out employing an electrophilic selenium species generated in situ through the reaction between SelectFluor® and organic diselenides. The formation of this electrophilic selenium species (RSe-F) was confirmed by heteronuclear NMR spectroscopy, and its reactivity was explored.
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Affiliation(s)
- Maurício Carpe Diem Ferreira Xavier
- Laboratório de Síntese Orgânica Limpa - LASOL, Centro de Ciências Químicas, Farmacêuticas e de Alimentos - CCQFA, Universidade Federal de Pelotas - UFPel Capão do Leão RS Brazil
| | - Eduardo Martarelo Andia Sandagorda
- Laboratório de Síntese Orgânica Limpa - LASOL, Centro de Ciências Químicas, Farmacêuticas e de Alimentos - CCQFA, Universidade Federal de Pelotas - UFPel Capão do Leão RS Brazil
| | | | - Ricardo Frederico Schumacher
- Laboratório de Síntese Orgânica Limpa - LASOL, Centro de Ciências Químicas, Farmacêuticas e de Alimentos - CCQFA, Universidade Federal de Pelotas - UFPel Capão do Leão RS Brazil
- Departamento de Química, Universidade Federal de Santa Maria - UFSM Santa Maria RS Brazil
| | - Márcio Santos Silva
- Laboratório de Síntese Orgânica Limpa - LASOL, Centro de Ciências Químicas, Farmacêuticas e de Alimentos - CCQFA, Universidade Federal de Pelotas - UFPel Capão do Leão RS Brazil
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7
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Ng YY, Tan LJ, Ng SM, Chai YT, Ganguly R, Du Y, Yeow EKL, Soo HS. Spectroscopic Characterization and Mechanistic Studies on Visible Light Photoredox Carbon–Carbon Bond Formation by Bis(arylimino)acenaphthene Copper Photosensitizers. ACS Catal 2018. [DOI: 10.1021/acscatal.8b02502] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yik Yie Ng
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Lisa Jiaying Tan
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Shue Mei Ng
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Yoke Tin Chai
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Rakesh Ganguly
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Yonghua Du
- Institute of Chemical and Engineering Sciences A*STAR, 1 Pesek Road, Singapore 627833
| | - Edwin Kok Lee Yeow
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Han Sen Soo
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
- Solar Fuels Laboratory, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798
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8
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Egami H, Masuda S, Kawato Y, Hamashima Y. Photofluorination of Aliphatic C–H Bonds Promoted by the Phthalimide Group. Org Lett 2018; 20:1367-1370. [DOI: 10.1021/acs.orglett.8b00133] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hiromichi Egami
- School of Pharmaceutical
Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan
| | - Shuya Masuda
- School of Pharmaceutical
Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan
| | - Yuji Kawato
- School of Pharmaceutical
Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan
| | - Yoshitaka Hamashima
- School of Pharmaceutical
Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan
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9
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Bume DD, Pitts CR, Ghorbani F, Harry SA, Capilato JN, Siegler MA, Lectka T. Ketones as directing groups in photocatalytic sp 3 C-H fluorination. Chem Sci 2017; 8:6918-6923. [PMID: 29147517 PMCID: PMC5637129 DOI: 10.1039/c7sc02703f] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 08/10/2017] [Indexed: 11/21/2022] Open
Abstract
The ubiquitous ketone carbonyl group generally deactivates substrates toward radical-based fluorinations, especially sites closest to it. Herein, ketones are used instead to direct aliphatic fluorination using Selectfluor, catalytic benzil, and visible light. Selective β- and γ-fluorination are demonstrated on rigid mono-, di-, tri-, and tetracyclic (steroidal) substrates employing both cyclic and exocyclic aliphatic ketones as directing groups.
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Affiliation(s)
- Desta Doro Bume
- Department of Chemistry , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA .
| | - Cody Ross Pitts
- Department of Chemistry , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA .
| | - Fereshte Ghorbani
- Department of Chemistry , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA .
| | - Stefan Andrew Harry
- Department of Chemistry , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA .
| | - Joseph N Capilato
- Department of Chemistry , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA .
| | - Maxime A Siegler
- Department of Chemistry , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA .
| | - Thomas Lectka
- Department of Chemistry , Johns Hopkins University , 3400 N. Charles St. , Baltimore , MD 21218 , USA .
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Lantaño B, Postigo A. Radical fluorination reactions by thermal and photoinduced methods. Org Biomol Chem 2017; 15:9954-9973. [DOI: 10.1039/c7ob02402a] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Radical fluorination reactions of aliphatic Csp3 and Csp2 atoms, decarboxylative fluorination, and fluorination of (hetero)aromatics can be accomplished with electrophilic fluorinating reagents such as Selectfluor and NFSI.
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Affiliation(s)
- Beatriz Lantaño
- Universidad de Buenos Aires
- Facultad de Farmacia y Bioquímica
- Departamento de Química Orgánica-Conicet-Buenos Aires
- Argentina
- Ciudad de Buenos Aires
| | - Al Postigo
- Universidad de Buenos Aires
- Facultad de Farmacia y Bioquímica
- Departamento de Química Orgánica-Conicet-Buenos Aires
- Argentina
- Ciudad de Buenos Aires
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