1
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Jung H, Choi J, Kim D, Lee JH, Ihee H, Kim D, Chang S. Photoinduced Group Transposition via Iridium-Nitrenoid Leading to Amidative Inner-Sphere Aryl Migration. Angew Chem Int Ed Engl 2024:e202408123. [PMID: 38871650 DOI: 10.1002/anie.202408123] [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] [Received: 04/29/2024] [Revised: 06/13/2024] [Accepted: 06/13/2024] [Indexed: 06/15/2024]
Abstract
We herein report a fundamental mechanistic investigation into photochemical metal-nitrenoid generation and inner-sphere transposition reactivity using organometallic photoprecursors. By designing Cp*Ir(hydroxamate)(Ar) complexes, we induced photo-initiated ligand activation, allowing us to explore the amidative σ(Ir-aryl) migration reactivity. A combination of experimental mechanistic studies, femtosecond transient absorption spectroscopy, and density functional theory (DFT) calculations revealed that the metal-to-ligand charge transfer enables the σ(N-O) cleavage, followed by Ir-acylnitrenoid generation. The final inner-sphere σ(Ir-aryl) group migration results in a net amidative group transposition.
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Affiliation(s)
- Hoimin Jung
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Jungkweon Choi
- Center for Advanced Reaction Dynamics, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Daniel Kim
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Jeong Hoon Lee
- Center for Advanced Reaction Dynamics, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Hyotcherl Ihee
- Center for Advanced Reaction Dynamics, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Dongwook Kim
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Sukbok Chang
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
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2
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Gu K, Yu C, Zhou W, Liu C. In Operando Visualization of Elementary Turnovers in Photocatalytic Organic Synthesis. J Phys Chem Lett 2024; 15:717-724. [PMID: 38214912 DOI: 10.1021/acs.jpclett.3c03109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2024]
Abstract
We report the in operando visualization of the photocatalytic turnovers on single eosin Y (EY) through a redox-induced photoblinking phenomenon. The photocatalytic cyclization of thiobenzamide (TB) catalyzed by EY was investigated. The analysis of the intensity-versus-time trajectories of single EYs revealed the kinetics and dynamics of the elementary photocatalytic turnovers and the heterogeneity of the activity of individual EYs. The quenching turnover time showed a fast population and a slow population, which could be attributed to the singlet and triplet states of photoexcited EY. The slow quenching turnovers were more dominant at higher TB concentrations. The activity heterogeneity of EYs was studied over a series of reactant concentrations. Excess quenching reagent was found to decrease the percentage of active EYs. The method can be broadly applied to studying the elementary processes of photocatalytic organic reactions in operando.
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Affiliation(s)
- Kai Gu
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, Ohio 44325, United States
| | - Christina Yu
- Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Wenqiao Zhou
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, Ohio 44325, United States
| | - Chunming Liu
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, Ohio 44325, United States
- Department of Chemistry, University of Akron, Akron, Ohio 44325, United States
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3
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Swords WB, Lee H, Park Y, Llamas F, Skubi KL, Park J, Guzei IA, Baik MH, Yoon TP. Highly Enantioselective 6π Photoelectrocyclizations Engineered by Hydrogen Bonding. J Am Chem Soc 2023; 145:27045-27053. [PMID: 38049954 PMCID: PMC10842740 DOI: 10.1021/jacs.3c10782] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/06/2023]
Abstract
Photochemical electrocyclization reactions are valued for both their ability to produce structurally complex molecules and their central role in elucidating fundamental mechanistic principles of photochemistry. We present herein a highly enantioselective 6π photoelectrocyclization catalyzed by a chiral Ir(III) photosensitizer. This transformation was successfully realized by engineering a strong hydrogen-bonding interaction between a pyrazole moiety on the catalyst and a basic imidazolyl ketone on the substrate. To shed light on the origin of stereoinduction, we conducted a comprehensive investigation combining experimental and computational mechanistic studies. Results from density functional theory calculations underscore the crucial role played by the prochirality and the torquoselectivity in the electrocyclization process as well as the steric demand in the subsequent [1,4]-H shift step. Our findings not only offer valuable guidance for developing chiral photocatalysts but also serve as a significant reference for achieving high levels of enantioselectivity in the 6π photoelectrocyclization reaction.
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Affiliation(s)
- Wesley B Swords
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Hanna Lee
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
| | - Yerin Park
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
| | - Franco Llamas
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Kazimer L Skubi
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
- Department of Chemistry, Carleton College, Northfield, Minnesota 55057, United States
| | - Jiyong Park
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
| | - Ilia A Guzei
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Mu-Hyun Baik
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea
| | - Tehshik P Yoon
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
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4
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LaPorte AJ, Feldner JE, Spies JC, Maher TJ, Burke MD. MIDA- and TIDA-Boronates Stabilize α-Radicals Through B-N Hyperconjugation. Angew Chem Int Ed Engl 2023; 62:e202309566. [PMID: 37540542 DOI: 10.1002/anie.202309566] [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] [Received: 07/05/2023] [Revised: 08/03/2023] [Accepted: 08/04/2023] [Indexed: 08/05/2023]
Abstract
Multifunctional organoboron compounds increasingly enable the simple generation of complex, Csp3 -rich small molecules. The ability of boron-containing functional groups to modify the reactivity of α-radicals has also enabled a myriad of chemical reactions. Boronic esters with vacant p-orbitals have a significant stabilizing effect on α-radicals due to delocalization of spin density into the empty orbital. The effect of coordinatively saturated derivatives, such as N-methyliminodiacetic acid (MIDA) boronates and counterparts, remains less clear. Herein, we demonstrate that coordinatively saturated MIDA and TIDA boronates stabilize secondary alkyl α-radicals via σB-N hyperconjugation in a manner that allows site-selective C-H bromination. DFT calculated radical stabilization energies and spin density maps as well as LED NMR kinetic analysis of photochemical bromination rates of different boronic esters further these findings. This work clarifies that the α-radical stabilizing effect of boronic esters does not only proceed via delocalization of radical character into vacant boron p-orbitals, but that hyperconjugation of tetrahedral boron-containing functional groups and their ligand electron delocalizing ability also play a critical role. These findings establish boron ligands as a useful dial for tuning reactivity at the α-carbon.
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Affiliation(s)
- Antonio J LaPorte
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Jack E Feldner
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Jan C Spies
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Tom J Maher
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Martin D Burke
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
- Carle Illinois College of Medicine, University of Illinois, Urbana, IL, 61820, USA
- Department of Biochemistry, University of Illinois, Urbana, IL, 61820, USA
- Arnold and Mable Beckman Institute, University of Illinois, Urbana, IL, 61820, USA
- Carl R. Woese Institute for Genomic Biology, University of Illinois, Urbana, IL, 61820, USA
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5
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Jung H, Kweon J, Suh JM, Lim MH, Kim D, Chang S. Mechanistic snapshots of rhodium-catalyzed acylnitrene transfer reactions. Science 2023:eadh8753. [PMID: 37471480 DOI: 10.1126/science.adh8753] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 06/26/2023] [Indexed: 07/22/2023]
Abstract
Rhodium acylnitrene complexes are widely implicated in catalytic C-H amidation reactions but have eluded isolation and structural characterization. To overcome this challenge, we designed a chromophoric octahedral rhodium complex with a bidentate dioxazolone ligand, in which photoinduced metal-to-ligand charge transfer initiates catalytic C-H amidation. X-ray photocrystallographic analysis of the Rh-dioxazolone complex allowed structural elucidation of the targeted Rh-acylnitrenoid and provided firm evidence that the singlet nitrenoid species is primarily responsible for acylamino transfer reactions. We also monitored in crystallo reaction of a nucleophile with the in situ generated Rh-acylnitrenoid, providing a crystallographically traceable reaction system to capture mechanistic snapshots of nitrenoid transfer.
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Affiliation(s)
- Hoimin Jung
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, South Korea
| | - Jeonguk Kweon
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, South Korea
| | - Jong-Min Suh
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
| | - Mi Hee Lim
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
| | - Dongwook Kim
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, South Korea
| | - Sukbok Chang
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, South Korea
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6
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Paolillo JM, Duke AD, Gogarnoiu ES, Wise DE, Parasram M. Anaerobic Hydroxylation of C(sp 3)-H Bonds Enabled by the Synergistic Nature of Photoexcited Nitroarenes. J Am Chem Soc 2023; 145:2794-2799. [PMID: 36696364 PMCID: PMC10032565 DOI: 10.1021/jacs.2c13502] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A photoexcited-nitroarene-mediated anaerobic C-H hydroxylation of aliphatic systems is reported. The success of this reaction is due to the bifunctional nature of the photoexcited nitroarene, which serves as the C-H bond activator and the oxygen atom source. Compared to previous methods, this approach is cost- and atom-economical due to the commercial availability of the nitroarene, the sole mediator of the reaction. Because of the anaerobic conditions of the transformation, a noteworthy expansion in substrate scope can be obtained compared to prior reports. Mechanistic studies support that the photoexcited nitroarenes engage in successive hydrogen atom transfer and radical recombination events with hydrocarbons, leading to N-arylhydroxylamine ether intermediates. Spontaneous fragmentation of these intermediates leads to the key oxygen atom transfer products.
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Affiliation(s)
- Joshua M Paolillo
- Department of Chemistry, New York University, New York, New York 10003, United States
| | - Alana D Duke
- Department of Chemistry, New York University, New York, New York 10003, United States
| | - Emma S Gogarnoiu
- Department of Chemistry, New York University, New York, New York 10003, United States
| | - Dan E Wise
- Department of Chemistry, New York University, New York, New York 10003, United States
| | - Marvin Parasram
- Department of Chemistry, New York University, New York, New York 10003, United States
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7
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Brown E, Mandzhieva I, TomHon PM, Theis T, Castellano FN. Triplet Photosensitized para-Hydrogen Induced Polarization. ACS CENTRAL SCIENCE 2022; 8:1548-1556. [PMID: 36439314 PMCID: PMC9686209 DOI: 10.1021/acscentsci.2c01003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Indexed: 06/16/2023]
Abstract
Despite its enormous utility in structural characterization, nuclear magnetic resonance (NMR) spectroscopy is inherently limited by low spin polarization. One method to address the low polarization is para-hydrogen (p-H2) induced polarization (PHIP) which uses the singlet spin isomer of H2 to generate disparate nuclear spin populations to amplify the associated NMR signals. PHIP often relies on thermal catalysis or, more infrequently, UV-activated catalytic hydrogenation. Light-activated hydrogenation enables direct and timed control over the hyperpolarization of target substrates, critical for identifying short-lived intermediates. Here, we use an established Ir(III) triplet photosensitizer (PS) to visible light sensitize the triplet ligand-field states in the d6-transition metal dihydride Ru(CO)(PPh3)3(H)2 (1). Excitation inside a 9.4 T NMR spectrometer with the PS and a 420 nm blue LED, under 3 atm of p-H2, successfully photosensitized hyperpolarization in 1 and in a range of unsaturated substrates at and below room temperature, up to 1630-fold. In otherwise identical experimental conditions without light activation, no polarization was realized in 1 or the substrates evaluated. We believe triplet-sensitized PHIP (Trip-PHIP) represents a facile experimental means for probing triplet sensitized light activation in transition metal catalysts possessing low-lying triplet ligand-field states, providing mechanistic insight of potentially tremendous value in chemical catalysis.
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8
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Swords WB, Chapman SJ, Hofstetter H, Dunn AL, Yoon TP. Variable Temperature LED-NMR: Rapid Insights into a Photocatalytic Mechanism from Reaction Progress Kinetic Analysis. J Org Chem 2022; 87:11776-11782. [PMID: 35969669 DOI: 10.1021/acs.joc.2c01479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A multitude of techniques are available to obtain a useful understanding of photocatalytic mechanisms. The combination of LED illumination with nuclear magnetic resonance spectroscopy (LED-NMR) provides a rapid, convenient means to directly monitor a photocatalytic reaction in situ. Herein, we describe a study of the mechanism of an enantioselective intermolecular [2 + 2] photocycloaddition catalyzed by a chiral Ir photocatalyst using LED-NMR. The data-rich output of this experiment is suitable for same-excess and variable time normalization analyses (VTNA). Together, these identified an unexpected change in mechanism between reactions conducted at ambient and cryogenic temperatures. At -78 °C, the kinetic data are consistent with the triplet rebound mechanism we previously proposed for this reaction, involving sensitization of maleimide and rapid reaction with a hydrogen-bound quinoline within the solvent cage. At room temperature, the cycloaddition instead proceeds through intracomplex energy transfer to the hydrogen-bound quinolone. These results highlight the potential sensitivity of photocatalytic reaction mechanisms to the precise reaction conditions and the further utility of LED-NMR as a fast, data-rich tool for their interrogation that compares favorably to conventional ex situ kinetic analyses.
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Affiliation(s)
- Wesley B Swords
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin53703, United States
| | - Steven J Chapman
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin53703, United States
| | - Heike Hofstetter
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin53703, United States
| | - Anna L Dunn
- Drug Product Development, GlaxoSmithKline, Upper Providence, Pennsylvania19426, United States
| | - Tehshik P Yoon
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin53703, United States
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9
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Wise DE, Gogarnoiu ES, Duke AD, Paolillo JM, Vacala TL, Hussain WA, Parasram M. Photoinduced Oxygen Transfer Using Nitroarenes for the Anaerobic Cleavage of Alkenes. J Am Chem Soc 2022; 144:15437-15442. [PMID: 35930615 DOI: 10.1021/jacs.2c05648] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Herein we report the anaerobic cleavage of alkenes into carbonyl compounds using nitroarenes as oxygen transfer reagents under visible light. This approach serves as a safe and practical alternative to mainstream oxidative cleavage protocols, such as ozonolysis and the Lemieux-Johnson reaction. A wide range of alkenes possessing oxidatively sensitive functionalities underwent anaerobic cleavage to generate carbonyl derivatives with high efficiency and regioselectivity. Mechanistic studies support that the transformation occurs via direct photoexcitation of the nitroarene followed by a nonstereospecific radical cycloaddition event with alkenes. This leads to 1,3,2- and 1,4,2-dioxazolidine intermediates that fragment to give the carbonyl products. A combination of radical clock experiments and in situ photoNMR spectroscopy revealed the identities of the key radical species and the putative aryl dioxazolidine intermediates, respectively.
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Affiliation(s)
- Dan E Wise
- Department of Chemistry, New York University, 24 Waverly Place, third floor, New York, New York 10003, United States
| | - Emma S Gogarnoiu
- Department of Chemistry, New York University, 24 Waverly Place, third floor, New York, New York 10003, United States
| | - Alana D Duke
- Department of Chemistry, New York University, 24 Waverly Place, third floor, New York, New York 10003, United States
| | - Joshua M Paolillo
- Department of Chemistry, New York University, 24 Waverly Place, third floor, New York, New York 10003, United States
| | - Taylor L Vacala
- Department of Chemistry, New York University, 24 Waverly Place, third floor, New York, New York 10003, United States
| | - Waseem A Hussain
- Department of Chemistry, New York University, 24 Waverly Place, third floor, New York, New York 10003, United States
| | - Marvin Parasram
- Department of Chemistry, New York University, 24 Waverly Place, third floor, New York, New York 10003, United States
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10
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Substrate Photoswitching for Rate Enhancement of an Organocatalytic Cyclization Reaction. European J Org Chem 2022. [DOI: 10.1002/ejoc.202200048] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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11
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Bramham JE, Zalar M, Golovanov AP. Controlled release and characterisation of photocaged molecules using in situ LED illumination in solution NMR spectroscopy. Chem Commun (Camb) 2022; 58:11973-11976. [DOI: 10.1039/d2cc04731d] [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
We demonstrate that photo-uncaging reactions triggered by LED illumination can be conveniently monitored in situ by solution NMR, offering new ways to characterise and optimise photocages.
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Affiliation(s)
- Jack E. Bramham
- Department of Chemistry, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester, Manchester, M13 9PL, UK
| | - Matja Zalar
- Department of Chemical Engineering, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester, Manchester, M13 9PL, UK
| | - Alexander P. Golovanov
- Department of Chemistry, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester, Manchester, M13 9PL, UK
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12
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Jayasekara GK, Antolini C, Smith MA, Jacoby DJ, Escolastico J, Girard N, Young BT, Hayes D. Mechanisms of the Cu(I)-Catalyzed Intermolecular Photocycloaddition Reaction Revealed by Optical and X-ray Transient Absorption Spectroscopies. J Am Chem Soc 2021; 143:19356-19364. [PMID: 34752703 DOI: 10.1021/jacs.1c07282] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The [2 + 2] photocycloaddition provides a simple, single-step route to cyclobutane moieties that would otherwise be disfavored or impossible due to ring strain and/or steric interactions. We have used a combination of optical and X-ray transient absorption spectroscopies to elucidate the mechanism of the Cu(I)-catalyzed intermolecular photocycloaddition reaction using norbornene and cyclohexene as model substrates. We find that for norbornene the reaction proceeds through an initial metal-to-ligand charge transfer (MLCT) state that persists for 18 ns before the metal returns to the monovalent oxidation state. The Cu K-edge spectrum continues to evolve until ∼5 μs and then remains unchanged for the 50 μs duration of the measurement, reflecting product formation and ligand dissociation. We hypothesize that the MLCT transition and reverse electron transfer serve to sensitize the triplet excited state of one of the norbornene ligands, which then dimerizes with the other to give the product. For the case of cyclohexene, however, we do not observe a charge transfer state following photoexcitation and instead find evidence for an increase in the metal-ligand bond strength that persists for several ns before product formation occurs. This is consistent with a mechanism in which ligand photoisomerization is the initial step, which was first proposed by Salomon and Kochi in 1974 to explain the stereoselectivity of the reaction. Our investigation reveals how this photocatalytic reaction may be directed along strikingly disparate trajectories by only very minor changes to the structure of the substrate.
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Affiliation(s)
- Gethmini K Jayasekara
- Department of Chemistry, University of Rhode Island, 45 Upper College Road, Kingston, Rhode Island 02881, United States
| | - Cali Antolini
- Department of Chemistry, University of Rhode Island, 45 Upper College Road, Kingston, Rhode Island 02881, United States
| | - Melissa A Smith
- Department of Chemistry, University of Rhode Island, 45 Upper College Road, Kingston, Rhode Island 02881, United States
| | - Danielle J Jacoby
- Department of Chemistry, University of Rhode Island, 45 Upper College Road, Kingston, Rhode Island 02881, United States
| | - Jacqueline Escolastico
- Department of Physical Sciences, Rhode Island College, 600 Mt Pleasant Avenue, Providence, Rhode Island 02908, United States
| | - Nathan Girard
- Department of Physical Sciences, Rhode Island College, 600 Mt Pleasant Avenue, Providence, Rhode Island 02908, United States
| | - Benjamin T Young
- Department of Physical Sciences, Rhode Island College, 600 Mt Pleasant Avenue, Providence, Rhode Island 02908, United States
| | - Dugan Hayes
- Department of Chemistry, University of Rhode Island, 45 Upper College Road, Kingston, Rhode Island 02881, United States
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13
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Kristinaityte K, Urbańczyk M, Mames A, Pietrzak M, Ratajczyk T. Photoreactivity of an Exemplary Anthracene Mixture Revealed by NMR Studies, including a Kinetic Approach. Molecules 2021; 26:6695. [PMID: 34771104 PMCID: PMC8587725 DOI: 10.3390/molecules26216695] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 10/28/2021] [Accepted: 11/03/2021] [Indexed: 11/16/2022] Open
Abstract
Anthracenes are an important class of acenes. They are being utilized more and more often in chemistry and materials sciences, due to their unique rigid molecular structure and photoreactivity. In particular, photodimerization can be harnessed for the fabrication of novel photoresponsive materials. Photodimerization between the same anthracenes have been investigated and utilized in various fields, while reactions between varying anthracenes have barely been investigated. Here, Nuclear Magnetic Resonance (NMR) spectroscopy is employed for the investigation of the photodimerization of two exemplary anthracenes: anthracene (A) and 9-bromoanthracene (B), in the solutions with only A or B, and in the mixture of A and B. Estimated k values, derived from the presented kinetic model, showed that the dimerization of A was 10 times faster in comparison with B when compounds were investigated in separate samples, and 2 times faster when compounds were prepared in the mixture. Notably, the photoreaction in the mixture, apart from AA and BB, additionally yielded a large amount of the AB mixdimer. Another important advantage of investigating a mixture with different anthracenes is the ability to estimate the relative reactivity for all the reactions under the same experimental conditions. This results in a better understanding of the photodimerization processes. Thus, the rational photofabrication of mix-anthracene-based materials can be facilitated, which is of crucial importance in the field of polymer and material sciences.
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Affiliation(s)
| | | | | | - Mariusz Pietrzak
- Institute of Physical Chemistry, Polish Academy of Sciences, PL-01224 Warsaw, Poland; (K.K.); (M.U.); (A.M.)
| | - Tomasz Ratajczyk
- Institute of Physical Chemistry, Polish Academy of Sciences, PL-01224 Warsaw, Poland; (K.K.); (M.U.); (A.M.)
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14
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Ji Y, Bottecchia C, Lévesque F, Narsimhan K, Lehnherr D, McMullen JP, Dalby SM, Xiao KJ, Reibarkh M. Benzylic Photobromination for the Synthesis of Belzutifan: Elucidation of Reaction Mechanisms Using In Situ LED-NMR. J Org Chem 2021; 87:2055-2062. [PMID: 34590859 DOI: 10.1021/acs.joc.1c01465] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A detailed mechanistic understanding of a benzylic photobromination en route to belzutifan (MK-6482, a small molecule for the treatment of renal cell carcinoma associated with von Hippel-Lindau syndrome) has been achieved using in situ LED-NMR spectroscopy in conjunction with kinetic analysis. Two distinct mechanisms of overbromination, namely, the ionic and radical pathways, have been revealed by this study. The behavior of the major reaction species, including reactants, intermediates, products, and side products, has been elucidated. Comprehensive understanding of both pathways informed and enabled mitigation of a major process risk: a sudden product decomposition. Detailed knowledge of the processes occurring during the reaction and their potential liabilities enabled the development of a robust photochemical continuous flow process implemented for commercial manufacturing.
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Affiliation(s)
- Yining Ji
- Analytical Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Cecilia Bottecchia
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - François Lévesque
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Karthik Narsimhan
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Dan Lehnherr
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Jonathan P McMullen
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Stephen M Dalby
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Kai-Jiong Xiao
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Mikhail Reibarkh
- Analytical Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
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15
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Prentice C, Morrisson J, Smith AD, Zysman-Colman E. Recent developments in enantioselective photocatalysis. Beilstein J Org Chem 2020; 16:2363-2441. [PMID: 33082877 PMCID: PMC7537410 DOI: 10.3762/bjoc.16.197] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Accepted: 09/09/2020] [Indexed: 01/02/2023] Open
Abstract
Enantioselective photocatalysis has rapidly grown into a powerful tool for synthetic chemists. This review describes the various strategies for creating enantioenriched products through merging enantioselective catalysis and photocatalysis, with a focus on the most recent developments and a particular interest in the proposed mechanisms for each. With the aim of understanding the scope of each strategy, to help guide and inspire further innovation in this field.
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Affiliation(s)
- Callum Prentice
- Organic Semiconductor Centre, EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, Fife, Scotland, KY16 9ST, United Kingdom
| | - James Morrisson
- Pharmaceutical Sciences, IMED Biotech Unit, AstraZeneca, Macclesfield SK102NA, United Kingdom
| | - Andrew D Smith
- Organic Semiconductor Centre, EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, Fife, Scotland, KY16 9ST, United Kingdom
| | - Eli Zysman-Colman
- Organic Semiconductor Centre, EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, Fife, Scotland, KY16 9ST, United Kingdom
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