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Lim SH, You H, Kim MJ, Wee KR, Cho DW. Triplet Energy Transfer (EnT)-Promoted 1,3-Dipolar Cycloaddition Reactions of N-(Trimethylsilyl)methylphthalimide with Electron-Deficient Alkynes and Alkenes. J Org Chem 2024; 89:13150-13166. [PMID: 39225314 DOI: 10.1021/acs.joc.4c01287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/04/2024]
Abstract
Triplet energy transfer (EnT)-promoted photochemical pathways, arisen by visible light and its photosensitizers, have gained significant attention as a complementary strategy for initiating organic transformations in photochemical reactions that are unlikely to occur through a single electron transfer (SET) process. In the present study, we investigated the triplet EnT-promoted 1,3-dipolar cycloaddition reactions of N-(trimethylsilyl)methylphthalimide with electron-deficient alkynyl and alkenyl dipolarophiles. The triplet excited state of N-(trimethylsilyl)methylphthalimide, promoted by the triplet EnT from thioxanthone (TXA) photosensitizer, underwent sequential intramolecular SET and carbon-to-oxygen migration of the silyl group to form azomethine ylide. This generated ylide cycloadded to alkynes or alkenes to regioselectively and stereospecifically produce a nitrogen-containing benzopyrrolizidine scaffold with multiple stereogenic centers. Crucially, the stereoselectivity of these cycloaddition reactions (i.e., endo versus exo addition) was influenced by the nature of the dipolarophiles.
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Affiliation(s)
- Suk Hyun Lim
- Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 38541, Republic of Korea
| | - Hayeon You
- Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 38541, Republic of Korea
| | - Min-Ji Kim
- Department of Advanced Materials Chemistry, Korea University, Sejong 30019, Republic of Korea
| | - Kyung-Ryang Wee
- Department of Advanced Materials Chemistry, Korea University, Sejong 30019, Republic of Korea
| | - Dae Won Cho
- Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 38541, Republic of Korea
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Adak S, Braley SE, Brown MK. Photochemical Reduction of Quinolines with γ-Terpinene. Org Lett 2024; 26:401-405. [PMID: 38169485 PMCID: PMC11027786 DOI: 10.1021/acs.orglett.3c04096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
The saturation of aromatic scaffolds is valuable for the synthesis of complex rings. Herein, we demonstrate a process for photochemical dearomative reduction of quinolines. The process involves capture of a quinoline excited state with γ-terpinene. Importantly, the reaction is chemoselective as other easily reduced functionalities such as halogens or alkenes do not undergo reduction. The mechanism of the reaction has also been investigated. Finally, the generality of the approach towards other substrates is demonstrated.
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Affiliation(s)
- Souvik Adak
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Sarah E Braley
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - M Kevin Brown
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States
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Rigotti T, Bach T. Bicyclo[2.1.1]hexanes by Visible Light-Driven Intramolecular Crossed [2 + 2] Photocycloadditions. Org Lett 2022; 24:8821-8825. [PMID: 36414533 DOI: 10.1021/acs.orglett.2c03606] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Bicyclo[2.1.1]hexanes have become increasingly popular building blocks in medicinal chemistry as bridged scaffolds that provide unexplored chemical space. We herein report a visible light-driven approach to these compounds that relies on an intramolecular crossed [2 + 2] photocycloaddition of styrene derivatives enabled by triplet energy transfer. Bicyclo[2.1.1]hexanes were obtained in good to high yields (19 examples, 61%-quantitative yield) and allowed for further functionalizations by consecutive reactions, thereby opening different pathways to decorate the aliphatic core structure.
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Affiliation(s)
- Thomas Rigotti
- Technical University of Munich, School of Natural Sciences, Department of Chemistry and Catalysis Research Center, Lichtenbergstrasse 4, 85747Garching, Germany
| | - Thorsten Bach
- Technical University of Munich, School of Natural Sciences, Department of Chemistry and Catalysis Research Center, Lichtenbergstrasse 4, 85747Garching, Germany
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Xiong Y, Großkopf J, Jandl C, Bach T. Visible Light-Mediated Dearomative Hydrogen Atom Abstraction/ Cyclization Cascade of Indoles. Angew Chem Int Ed Engl 2022; 61:e202200555. [PMID: 35213774 PMCID: PMC9314014 DOI: 10.1002/anie.202200555] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Indexed: 11/24/2022]
Abstract
The photochemical synthesis of yet unknown 2‐oxospiro[azetidine‐3,3′‐indolines] (17 examples, 80–95 % yield), 2,4‐dioxospiro[azetidine‐3,3′‐indolines] (eight examples, 87–97 % yield), and 1‐oxo‐1,3‐dihydrospiro[indene‐2,3′‐indolines] (17 examples, 85–97 % yield) is described. Starting from readily accessible 3‐substituted indoles, a dearomatization of the indole core was accomplished upon irradiation at λ=420 nm in the presence of thioxanthen‐9‐one (10 mol%) as the sensitizer. Based on mechanistic evidence (triplet energy determination, deuteration experiments, by‐product analysis) it is proposed that the reaction proceeds by energy transfer via a 1,4‐ or 1,5‐diradical intermediate. The latter intermediates are formed by excited state hydrogen atom transfer from suitable alkyl groups within the C3 substituent to the indole C2 carbon atom. Subsequent ring closure proceeds with pronounced diastereoselectivity to generate a 4‐ or 5‐membered spirocyclic dearomatized product with several options for further functionalization.
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Affiliation(s)
- Yang Xiong
- Department Chemie and Catalysis Research Center (CRC), School of Natural Sciences, Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany
| | - Johannes Großkopf
- Department Chemie and Catalysis Research Center (CRC), School of Natural Sciences, Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany
| | - Christian Jandl
- Department Chemie and Catalysis Research Center (CRC), School of Natural Sciences, Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany
| | - Thorsten Bach
- Department Chemie and Catalysis Research Center (CRC), School of Natural Sciences, Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany
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Xiong Y, Großkopf J, Jandl C, Bach T. Visible Light‐Mediated Dearomative Hydrogen Atom Abstraction/ Cyclization Cascade of Indoles. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202200555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Yang Xiong
- Technische Universität München: Technische Universitat Munchen Chemistry GERMANY
| | - Johannes Großkopf
- Technische Universität München: Technische Universitat Munchen Chemistry GERMANY
| | - Christian Jandl
- Technische Universität München: Technische Universitat Munchen Chemistry GERMANY
| | - Thorsten Bach
- Technische Universität München Lehrstuhl für Organische Chemie I Lichtenbergstr. 4 85747 Garching GERMANY
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Rigotti T, Schwinger DP, Graßl R, Jandl C, Bach T. Enantioselective crossed intramolecular [2+2] photocycloaddition reactions mediated by a chiral chelating Lewis acid. Chem Sci 2022; 13:2378-2384. [PMID: 35310494 PMCID: PMC8864722 DOI: 10.1039/d2sc00113f] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Accepted: 02/01/2022] [Indexed: 12/01/2022] Open
Abstract
In intramolecular [2+2] photocycloaddition reactions, the two tethered olefins can approach each other in a straight or in a crossed fashion. Despite the fact that the latter reaction mode leads to intriguing, otherwise inaccessible bridged skeletons, there has so far not been any enantioselective variants thereof. This study concerned the crossed [2+2]-photocycloaddition of 2-(alkenyloxy)cyclohex-2-enones to bridged cyclobutanes. It was found that the reaction could be performed with high enantioselectivity (80-94% ee) under visible light conditions when employing a chiral rhodium Lewis acid as a catalyst (2 mol%).
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Affiliation(s)
- Thomas Rigotti
- School of Natural Sciences, Department Chemie, Catalysis Research Center (CRC), Technische Universität München 85747 Garching Germany +49 89 28913315 +49 89 28913330
| | - Daniel P Schwinger
- School of Natural Sciences, Department Chemie, Catalysis Research Center (CRC), Technische Universität München 85747 Garching Germany +49 89 28913315 +49 89 28913330
| | - Raphaela Graßl
- School of Natural Sciences, Department Chemie, Catalysis Research Center (CRC), Technische Universität München 85747 Garching Germany +49 89 28913315 +49 89 28913330
| | - Christian Jandl
- School of Natural Sciences, Department Chemie, Catalysis Research Center (CRC), Technische Universität München 85747 Garching Germany +49 89 28913315 +49 89 28913330
| | - Thorsten Bach
- School of Natural Sciences, Department Chemie, Catalysis Research Center (CRC), Technische Universität München 85747 Garching Germany +49 89 28913315 +49 89 28913330
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Sicignano M, Rodríguez RI, Alemán J. Recent Visible Light and Metal Free Strategies in [2+2] and [4+2] Photocycloadditions. European J Org Chem 2021; 2021:3303-3321. [PMID: 34248414 PMCID: PMC8252406 DOI: 10.1002/ejoc.202100518] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Revised: 05/17/2021] [Indexed: 01/17/2023]
Abstract
When aiming to synthesize molecules with elevated molecular complexity starting from relatively simple starting materials, photochemical transformations represent an open avenue to circumvent analogous multistep procedures. Specifically, light-mediated cycloadditions remain as powerful tools to generate new bonds begotten from non-very intuitive disconnections, that alternative thermal protocols would not offer. In response to the current trend in both industrial and academic research pointing towards green and sustainable processes, several strategies that meet these requirements are currently available in the literature. This Minireview summarizes [2+2] and [4+2] photocycloadditions that do not require the use of metal photocatalysts by means of alternative strategies. It is segmented according to the cycloaddition type in order to give the reader a friendly approach and we primarily focus on the most recent developments in the field carried out using visible light, a general overview of the mechanism in each case is offered as well.
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Affiliation(s)
- Marina Sicignano
- Organic Chemistry DepartmentMódulo 1Universidad Autónoma de Madrid28049MadridSpain
| | - Ricardo I. Rodríguez
- Organic Chemistry DepartmentMódulo 1Universidad Autónoma de Madrid28049MadridSpain
| | - José Alemán
- Organic Chemistry DepartmentMódulo 1Universidad Autónoma de Madrid28049MadridSpain
- Institute for Advanced Research in Chemical Sciences (IAdChem)Universidad Autónoma de Madrid28049MadridSpain
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Hofmann AJ, Niederegger L, Hess CR. Neighbouring effects on catalytic epoxidation by Fe-cyclam in M 2-PDIxCy complexes. Dalton Trans 2020; 49:17642-17648. [PMID: 33226393 DOI: 10.1039/d0dt03758c] [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
The unsymmetric PDIeCy ligand, featuring pyridinediimine and cylam sites, can be selectively metalated. Complementing the diiron compound, we have synthesized two heterobimetallic isomers, [ZnPDIFeCy(PDIeCy)(OTf)4] (3) and [FePDIZnCy(PDIeCy)(OTf)4] (4), and a dizinc complex, [Zn2(PDIeCy)(OTf)4] (5). Olefin epoxidation by the series of complexes was investigated. The M-PDI site influences the reactivity of the M-cyclam, resulting in increased activity toward enones.
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Affiliation(s)
- Andreas J Hofmann
- Technische Universität München, Department of Chemistry and Catalysis Research Center, 85747 Garching, Germany.
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