1
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Hipwell VM, Garcia-Garibay MA. Mechanistic Studies of Adamantylacetophenones with Competing Reaction Pathways in Solution and in the Crystalline Solid State. J Org Chem 2019; 84:11103-11113. [PMID: 31412205 DOI: 10.1021/acs.joc.9b01720] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Photochemical reactions in crystals occur under conditions of highly restricted molecular mobility such that only one product is generally obtained, even when there are many others that can be observed in the gas phase or in solution. A series of 2-(1-adamantyl)-o-alkyl-acetophenones with γ-hydrogen atoms on both the adamantyl and ortho aromatic groups was selected to determine whether one can engineer and observe competing Norrish type II reaction pathways in the crystalline state. It was shown that excited state competition for hydrogen abstraction between secondary adamantyl and benzylic hydrogens is affected not only by the relative bond dissociation energies but also by the molecular conformation in the crystal. The subsequent fate of the resulting biradical species is determined by competition between radical recombination to form the photoproduct and reverse hydrogen atom transfer to regenerate the starting ketone. Crystallographic information, photoproduct distributions in solution and in the solid state, and the results of multiple mechanistic experiments, including transient absorption spectroscopy in acetonitrile and with nanocrystals suspended in water, are reported. The results demonstrate that it is possible to engineer competing reactions in crystals and that consideration of all of the aforementioned factors is necessary to account for the observed photoproduct selectivity.
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Affiliation(s)
- Vince M Hipwell
- Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095-1569 , United States
| | - Miguel A Garcia-Garibay
- Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095-1569 , United States
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2
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Fujino S, Yamaji M, Marciniak B. Laser photolysis studies of ω-bond dissociation in aromatic carbonyls of five-membered rings induced by triplet sensitization. J Photochem Photobiol A Chem 2018. [DOI: 10.1016/j.jphotochem.2018.07.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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3
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Shi W, Zou G. Palladium-Catalyzed Room Temperature Acylative Cross-Coupling of Activated Amides with Trialkylboranes. Molecules 2018; 23:E2412. [PMID: 30241341 PMCID: PMC6222728 DOI: 10.3390/molecules23102412] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 09/16/2018] [Accepted: 09/18/2018] [Indexed: 11/16/2022] Open
Abstract
A highly efficient acylative cross-coupling of trialkylboranes with activated amides has been effected at room temperature to give the corresponding alkyl ketones in good to excellent yields by using 1,3-bis(2,6-diisopropyl)phenylimidazolylidene and 3-chloropyridine co-supported palladium chloride, the PEPPSI catalyst, in the presence of K₂CO₃ in methyl tert-butyl ether. The scope and limitations of the protocol were investigated, showing good tolerance of acyl, cyano, and ester functional groups in the amide counterpart while halo group competed via the classical Suzuki coupling. The trialkylboranes generated in situ by hydroboration of olefins with BH₃ or 9-BBN performed similarly to those separately prepared, making this protocol more practical.
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Affiliation(s)
- Weijia Shi
- School of Chemistry & Molecular Engineering, East China University of Science & Technology, 130 Meilong Rd, Shanghai 200237, China.
| | - Gang Zou
- School of Chemistry & Molecular Engineering, East China University of Science & Technology, 130 Meilong Rd, Shanghai 200237, China.
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4
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Boice GN, Garakyaraghi S, Patrick BO, Sanz CA, Castellano FN, Hicks RG. Diastereomerically Differentiated Excited State Behavior in Ruthenium(II) Hexafluoroacetylacetonate Complexes of Diphenyl Thioindigo Diimine. Inorg Chem 2018; 57:1386-1397. [DOI: 10.1021/acs.inorgchem.7b02803] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Geneviève N. Boice
- Department of Chemistry, University of Victoria, PO Box 3065 STN CSC, Victoria, British
Columbia V8W 3V6, Canada
| | - Sofia Garakyaraghi
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Brian O. Patrick
- Crystallography Laboratory, Department
of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Corey A. Sanz
- Department of Chemistry, University of Victoria, PO Box 3065 STN CSC, Victoria, British
Columbia V8W 3V6, Canada
| | - Felix N. Castellano
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Robin G. Hicks
- Department of Chemistry, University of Victoria, PO Box 3065 STN CSC, Victoria, British
Columbia V8W 3V6, Canada
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5
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Yamaji M, Horimoto A, Marciniak B. Laser photolysis studies of ω-bond dissociation in aromatic carbonyls with a C-C triple bond stimulated by triplet sensitization. Phys Chem Chem Phys 2017. [PMID: 28638898 DOI: 10.1039/c7cp02758c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have prepared three types of carbonyl compounds, benzoylethynylmethyl phenyl sulfide (2@SPh), (p-benzoyl)phenylethynylmethyl phenyl sulfide (3@SPh) and p-(benzoylethynyl)benzyl phenyl sulfide (4@SPh) with benzoyl and phenylthiylmethyl groups, which are interconnected with a C-C triple bond and a phenyl ring. Laser flash photolysis of 3@SPh and 4@SPh in acetonitrile provided the transient absorption spectra of the corresponding triplet states where no chemical reactions were recognized. Upon laser flash photolysis of 2@SPh, the absorption band due to the phenylthiyl radical (PTR) was obtained, indicating that the C-S bond cleaved in the excited state. Triplet sensitization of these carbonyl compounds using acetone and xanthone was conducted using laser photolysis techniques. The formation of triplet 3@SPh was seen in the transient absorption, whereas the PTR formation was observed for 2@SPh and 4@SPh, indicating that the triplet states were reactive for the C-S bond dissociation. The C-S bond dissociation mechanism for 4@SPh upon triplet sensitization is discussed in comparison with those for 2@SPh and 3@SPh.
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Affiliation(s)
- Minoru Yamaji
- Division of Molecular Science, Graduate School of Science and Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan.
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6
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Ayitou AJL, Flynn K, Jockusch S, Khan SI, Garcia-Garibay MA. Structure–Kinetics Correlations in Isostructural Crystals of α-(ortho-Tolyl)-acetophenones: Pinning Down Electronic Effects Using Laser-Flash Photolysis in the Solid State. J Am Chem Soc 2016; 138:2644-8. [DOI: 10.1021/jacs.5b11657] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Anoklase J.-L. Ayitou
- Department
of Chemistry and Biochemistry, University of California, Los Angeles, Los
Angeles, California 90095, United States
| | - Kristen Flynn
- Department
of Chemistry and Biochemistry, University of California, Los Angeles, Los
Angeles, California 90095, United States
| | - Steffen Jockusch
- Department
of Chemistry, Columbia University, New York, New York 10027, United States
| | - Saeed I. Khan
- Department
of Chemistry and Biochemistry, University of California, Los Angeles, Los
Angeles, California 90095, United States
| | - Miguel A. Garcia-Garibay
- Department
of Chemistry and Biochemistry, University of California, Los Angeles, Los
Angeles, California 90095, United States
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7
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Ranaweera RAAU, Weragoda GK, Bain J, Watanabe S, Abe M, Gudmundsdottir AD. Photolysis of acetophenone derivatives with α-cyclopropyl substituents. J PHYS ORG CHEM 2014. [DOI: 10.1002/poc.3389] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
| | | | - John Bain
- Department of Chemistry; University of Cincinnati; Cincinnati OH 45221-0172 USA
| | - Shinji Watanabe
- Department of Chemistry, Graduate School of Science; Hiroshima University; 1-3-1 Kagamiyama Higashi-Hiroshima Hiroshima 739 -8526 Japan
| | - Manabu Abe
- Department of Chemistry, Graduate School of Science; Hiroshima University; 1-3-1 Kagamiyama Higashi-Hiroshima Hiroshima 739 -8526 Japan
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8
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Bucher G, Bresolí-Obach R, Brosa C, Flors C, Luis JG, Grillo TA, Nonell S. β-Phenyl quenching of 9-phenylphenalenones: a novel photocyclisation reaction with biological implications. Phys Chem Chem Phys 2014; 16:18813-20. [DOI: 10.1039/c4cp02783c] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
β-Phenyl quenching of 9-phenylphenalenones leads to the reversible formation of naphthoxanthenes and eventually to stable naphthoxanthenyl radicals or naphthoxanthenium cations.
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Affiliation(s)
- Götz Bucher
- WestCHEM
- School of Chemistry
- University of Glasgow
- Glasgow G12 8QQ, UK
| | | | - Carme Brosa
- Institut Químic de Sarrià
- Universitat Ramon Llull
- Barcelona, Spain
| | - Cristina Flors
- Institut Químic de Sarrià
- Universitat Ramon Llull
- Barcelona, Spain
- IMDEA Nanociencia
- E-28049 Madrid, Spain
| | - Javier G. Luis
- Instituto Universitario de Bio-Orgánica “Antonio González”
- La Laguna, Tenerife, Spain
- Departamento de Química Orgánica
- Facultad de Farmacia
- La Laguna, Tenerife, Spain
| | - Teresa A. Grillo
- Instituto Universitario de Bio-Orgánica “Antonio González”
- La Laguna, Tenerife, Spain
- Departamento de Química Orgánica
- Facultad de Farmacia
- La Laguna, Tenerife, Spain
| | - Santi Nonell
- Institut Químic de Sarrià
- Universitat Ramon Llull
- Barcelona, Spain
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9
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Anamimoghadam O, Symes MD, Busche C, Long DL, Caldwell ST, Flors C, Nonell S, Cronin L, Bucher G. Naphthoxanthenyl, a New Stable Phenalenyl Type Radical Stabilized by Electronic Effects. Org Lett 2013; 15:2970-3. [DOI: 10.1021/ol401117g] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ommid Anamimoghadam
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - Mark D. Symes
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - Christoph Busche
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - De-Liang Long
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - Stuart T. Caldwell
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - Cristina Flors
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - Santi Nonell
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - Leroy Cronin
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
| | - Götz Bucher
- WestCHEM, School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom, and Grup d’Enginyeria Molecular, Institut Químic de Sarrià, Universitat Ramon Llull, E-08017 Barcelona, Spain
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10
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Cuquerella MC, Lhiaubet-Vallet V, Cadet J, Miranda MA. Benzophenone photosensitized DNA damage. Acc Chem Res 2012; 45:1558-70. [PMID: 22698517 DOI: 10.1021/ar300054e] [Citation(s) in RCA: 169] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Although the carcinogenic potential of ultraviolet radiation is well-known, UV light may interact with DNA by direct absorption or through photosensitization by endogenous or exogenous chromophores. These chromophores can extend the "active" fraction of the solar spectrum to the UVA region and beyond, which means that photosensitizers increase the probability of developing skin cancer upon exposure to sunlight. Therefore researchers would like to understand the mechanisms involved in photosensitized DNA damage both to anticipate possible photobiological risks and to design tailor-made photoprotection strategies. In this context, photosensitized DNA damage can occur through a variety of processes including electron transfer, hydrogen abstraction, triplet-triplet energy transfer, or generation of reactive oxygen species. In this Account, we have chosen benzophenone (BP) as a classical and paradigmatic chromophore to illustrate the different lesions that photosensitization may prompt in nucleosides, in oligonucleotides, or in DNA. Thus, we discuss in detail the accumulated mechanistic evidence of the BP-photosensitized reactions of DNA or its building blocks obtained by our group and others. We also include ketoprofen (KP), a BP-derivative that possesses a chiral center, to highlight the stereodifferentiation in the key photochemical events, revealed through the dynamics of the reactive triplet excited state ((3)KP*). Our results show that irradiation of the BP chromophore in the presence of DNA or its components leads to nucleobase oxidations, cyclobutane pyrimidine dimer formation, single strand breaks, DNA-protein cross-links, or abasic sites. We attribute the manifold photoreactivity of BP to its well established photophysical properties: (i) it absorbs UV light, up to 360 nm; (ii) its intersystem crossing quantum yield (ϕ(ISC)) is almost 1; (iii) the energy of its nπ* lowest triplet excited state (E(T)) is ca. 290 kJ mol(-1); (iv) it produces singlet oxygen ((1)O(2)) with a quantum yield (ϕ(Δ)) of ca. 0.3. For electron transfer and singlet oxygen reactions, we focused on guanine, the nucleobase with the lowest oxidation potential. Among the possible oxidative processes, electron transfer predominates. Conversely, triplet-triplet energy transfer occurs mainly from (3)BP* to thymine, the base with the lowest lying triplet state in DNA. This process results in the formation of cyclobutane pyrimidine dimers, but it also competes with the Paternò-Büchi reaction in nucleobases or nucleosides, giving rise to oxetanes as a result of crossed cycloadditions. Interestingly, we have found significant stereodifferentiation in the quenching of the KP triplet excited state by both 2'-deoxyguanosine and thymidine. Based on these results, this chromophore shows potential as a (chiral) probe for the investigation of electron and triplet energy transport in DNA.
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Affiliation(s)
- M. Consuelo Cuquerella
- Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia, 46022 Valencia, Spain
| | - Virginie Lhiaubet-Vallet
- Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia, 46022 Valencia, Spain
| | - Jean Cadet
- Institut Nanosciences et Cryogénie, CEA/Grenoble, F-38054 Grenoble Cedex 9, France
| | - Miguel A. Miranda
- Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia, 46022 Valencia, Spain
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11
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Kuzmanich G, Vogelsberg CS, Maverick EF, Netto-Ferreira JC, Scaiano JC, Garcia-Garibay MA. Reaction Mechanism in Crystalline Solids: Kinetics and Conformational Dynamics of the Norrish Type II Biradicals from α-Adamantyl-p-Methoxyacetophenone. J Am Chem Soc 2011; 134:1115-23. [DOI: 10.1021/ja2090004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Gregory Kuzmanich
- Department of Chemistry and
Biochemistry, University of California,
Los Angeles, California 90095-1559, United States
| | - Cortnie S. Vogelsberg
- Department of Chemistry and
Biochemistry, University of California,
Los Angeles, California 90095-1559, United States
| | - Emily F. Maverick
- Department of Chemistry and
Biochemistry, University of California,
Los Angeles, California 90095-1559, United States
| | - José Carlos Netto-Ferreira
- Department of Chemistry and
Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
| | - J. C. Scaiano
- Department of Chemistry and
Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
| | - Miguel A. Garcia-Garibay
- Department of Chemistry and
Biochemistry, University of California,
Los Angeles, California 90095-1559, United States
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12
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Ma C, Kwok W, An HY, Guan X, Fu M, Toy P, Phillips D. A Time-Resolved Spectroscopic Study of the Bichromophoric Phototrigger 3′,5′-Dimethoxybenzoin Diethyl Phosphate: Interaction Between the Two Chromophores Determines the Reaction Pathway. Chemistry 2010; 16:5102-18. [DOI: 10.1002/chem.200902891] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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13
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Bucher G. Addition of the Carbonyl Oxygen to the ipso- or ortho-Carbon Atoms of the β-Phenyl Ring Followed by Intersystem Crossing and Rapid Relaxation to the Ground-State Ketones: A Mechanism for β-Phenyl Quenching of the First Triplet Excited States of Derivatives of β-Phenylpropiophenone. J Phys Chem A 2008; 112:5411-7. [DOI: 10.1021/jp711266z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Götz Bucher
- Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Universitätsstr. 150, D-44801 Bochum, Germany
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14
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Klima RF, Jadhav AV, Singh PND, Chang M, Vanos C, Sankaranarayanan J, Vu M, Ibrahim N, Ross E, McCloskey S, Murthy RS, Krause JA, Ault BS, Gudmundsdóttir AD. Photoinduced C−N Bond Cleavage in 2-Azido-1,3-diphenyl-propan-1-one Derivatives: Photorelease of Hydrazoic Acid. J Org Chem 2007; 72:6372-81. [PMID: 17655357 DOI: 10.1021/jo070558q] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Photolysis of 3-azido-1,3-diphenyl-propan-1-one (1a) in toluene yields 1,3-diphenyl-propen-1-one (2), whereas irradiation of 3-azido-2,2-dimethyl-1,3-diphenyl-propan-1-one (1b) results in the formation of mainly 2,2-dimethyl-1,3-diphenyl-propan-1-one. Laser flash photolysis (308 nm) of 1a,b in acetonitrile reveals a transient absorption (lambda max = approximately 310 nm) due to the formation of radicals 4a and 4b, respectively, which have lifetimes of approximately 14 micros at ambient temperature. TD-DFT calculations (B3LYP/6-31+G(d)) reveal that the first and second excited states of the triplet ketone (T1K (n,pi*) and T2K (pi,pi*)) in azide 1a are almost degenerate, at approximately 74 and 76 kcal/mol above the ground state (S0), respectively. Similarly, azide 1b has T1K and T2K 75 and 82 kcal/mol above S0, respectively. The calculated transition state for cleaving the C-N bond is located 71 and 74 kcal/mol above S0 in azides 1a and 1b, respectively. The calculated bond dissociation energies for breaking the C-N bond are 55 and 58 kcal/mol for azides 1a and 1b, respectively, making C-N bond breakage accessible from T1K in azides 1 at ambient temperature. In comparison, the irradiation of azides 1 in argon matrices at 14 K lead to the formation of the corresponding triplet alkyl nitrenes (1-n), via intramolecular energy transfer from T2K. The characterization of 1-n was supported by isotope labeling, IR spectroscopy, and molecular modeling.
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Affiliation(s)
- Rodney F Klima
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221-0172, USA
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Abad S, Bosca F, Domingo LR, Gil S, Pischel U, Miranda MA. Triplet Reactivity and Regio-/Stereoselectivity in the Macrocyclization of Diastereomeric Ketoprofen−Quencher Conjugates via Remote Hydrogen Abstractions. J Am Chem Soc 2007; 129:7407-20. [PMID: 17508750 DOI: 10.1021/ja0712827] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Intramolecular excited triplet state interactions in diastereomeric compounds composed of a benzophenone chromophore (ketoprofen) and various hydrogen donor moieties (tetrahydrofuran, isopropylbenzene) have been investigated by laser flash photolysis. The rate constants for hydrogen abstraction by excited triplet benzophenone are in the order of 10(4)-10(5) s(-1), with the highest reactivity for the tetrahydrofuran residue. A remarkable diastereodifferentiation, expressed in the triplet lifetimes of the carbonyl chromophore (e.g., 1.6 versus 2.7 micros), has been found for these compounds. With an alkylaromatic moiety as donor, related effects have been observed, albeit strongly dependent on the length of the spacer. The reactivity trend for the initial hydrogen transfer step is paralleled by the quantum yields of the overall photoreaction. The biradicals, formed via remote hydrogen abstraction, undergo intramolecular recombination to macrocyclic ring systems. The new photoproducts have been isolated and characterized by NMR spectroscopy. The stereochemistry of the macrocycles, which contain up to four asymmetric carbons, has been unambiguously assigned on the basis of single-crystal structures and/or NOE effects. Interestingly, a highly regio- and stereoselective macrocyclization has been found for the ketoprofen-tetrahydrofuran conjugates, where hydrogen abstraction from the less substituted carbon is exclusive; cisoid ring junction is always preferred over the transoid junction. The photoreaction is less regioselective for compounds with an isopropylbenzene residue. The reactivity and selectivity trends have been rationalized by DFT (B3LYP/6-31G*) calculations.
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Affiliation(s)
- Sergio Abad
- Instituto de Tecnología Química, UPV-CSIC, Universidad Politécnica de Valencia, Av. de los Naranjos s/n, E-46022 Valencia, Spain
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