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5 results on '"Fréneau A"'

1. The Paternò-Büchi reaction—Mechanisms and application to organic synthesis

Author

Norbert Hoffmann, Maxime Fréneau, Institut de Chimie Moléculaire de Reims - UMR 7312 (ICMR), SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), and Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)

Subjects
chemistry.chemical_classification, Reaction mechanism, Addition reaction, [CHIM.ORGA]Chemical Sciences/Organic chemistry, 010405 organic chemistry, Alkene, Organic Chemistry, 010402 general chemistry, Photochemistry, 01 natural sciences, Catalysis, Paternò–Büchi reaction, 0104 chemical sciences, chemistry.chemical_compound, Electron transfer, chemistry, Computational chemistry, [CHIM]Chemical Sciences, Organic synthesis, Stereoselectivity, Povarov reaction, Physical and Theoretical Chemistry
Abstract

International audience; The [2 + 2] photocycloaddition between an electronically excited carbonyl compound and an alkene leading to oxetanes (Paternò-Büchi reaction) is one of the most investigated organic photochemical reaction. Regio-, stereo- and site selectivities are discussed as a consequence of the reaction mechanism. Spin multiplicity and electron transfer have a significant impact on the outcome of the reaction. Typical carbonyl and alkene reaction partners are presented indicating scope and limitation of the reaction. The Paternò-Büchi reaction possesses particular interest for being applied to organic synthesis, considering the difficulty for non-photochemical reactions to obtain oxetanes, with or without stereoselectivity. Mechanistic details are particularly focused. It has been applied as key step in various multi-step syntheses.

Published
2017
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2. Photochemical reactivity of phenyl (methyl-tetrazolyl) ketone – hydrogen atom transfer vs. electron transfer

Author

Mario Andrés Gomez Fernandez, Corentin Lefebvre, Claire Richard, Norbert Hoffmann, Maxime Fréneau, SIGMA Clermont (SIGMA Clermont), Institut de Chimie de Clermont-Ferrand (ICCF), SIGMA Clermont (SIGMA Clermont)-Institut de Chimie du CNRS (INC)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), Institut de Chimie Moléculaire de Reims - UMR 7312 (ICMR), Université de Reims Champagne-Ardenne (URCA)-Institut de Chimie du CNRS (INC)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), Université de Reims Champagne-Ardenne (URCA)-Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)-SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-SIGMA Clermont (SIGMA Clermont), Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS), SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), and Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Cyclohexane, Pinacol, Diradical, [CHIM.ORGA]Chemical Sciences/Organic chemistry, Radical, 02 engineering and technology, General Chemistry, 010402 general chemistry, 021001 nanoscience & nanotechnology, Photochemistry, 01 natural sciences, Catalysis, 0104 chemical sciences, [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, chemistry.chemical_compound, Electron transfer, Ketyl, chemistry, Yield (chemistry), Materials Chemistry, Flash photolysis, [CHIM]Chemical Sciences, [PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph], 0210 nano-technology
Abstract

International audience; Phenyl (methyl-tetrazolyl) ketone (1) is a synthesis intermediate of tetrazolyloxime fungicides and can also be generated upon their irradiation. Its photolysis is highly solvent-dependent, which prompted us to investigate the reaction mechanism more deeply. The nanosecond laser flash photolysis of 1 yielded the triplet excited state (λmax = 390/570 nm) immediately after the pulse. This was later converted into different secondary species that were identified using their specific reactivity as well as product studies. The ketyl radical (λmax = 315/475 nm) was generated in less than 0.02 μs in a good H-donor solvent such as 2-propanol and in around 0.06 μs in cyclohexane, a medium H-donor solvent. In 2-propanol, ketyl radicals decayed by a second order reaction to yield pinacol (yield 45%); in contrast, in cyclohexane, they decayed by a second order reaction in the bulk, leading to the formation of pinacol (yield 21%), and by recombination with the cyclohexyl radical in the cage in an apparent first order reaction to generate an adduct (yield 10%). In a polar and non H-atom donor solvent such as acetonitrile, the zwitterionic diradical (λmax = 460 nm) was formed in 0.6 μs with the final formation of an atypical dimer. Thus, two mechanisms of hydrogen atom transfer were observed. In the polar acetonitrile solvent, a two-step process occurred, where an electron was transferred first, followed by a proton. In the less polar 2-propanol and non-polar cyclohexane solvents, a one-step process occurred, where an electron and a proton were simultaneously transferred.

Published
2019
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3. The structure of electronically excited α,β-unsaturated lactones

Author

Manabu Abe, Norbert Hoffmann, Pascal de Sainte-Claire, and Maxime Fréneau

Subjects
010405 organic chemistry, Chemistry, Organic Chemistry, Substituent, Ab initio, Dihedral angle, 010402 general chemistry, Ring (chemistry), Photochemistry, 01 natural sciences, 3. Good health, 0104 chemical sciences, Crystallography, chemistry.chemical_compound, Excited state, Density functional theory, Reactivity (chemistry), Physical and Theoretical Chemistry, Triplet state
Abstract

better knowledge of the structure of the electronically excited state of substrates is indispensable for the understanding and optimization of photochemical reactions. For this study, triplet energies of a variety of α,β-unsaturated γ-lactones (furanones) as well as the structures of the vibrationally relaxed triplet state (T1) have been determined using ab initio coupled-cluster (CCSD) method and/or density functional theory (DFT) calculation. A twist of the original planar structure around C = C bond is found in the relaxed triplet state, π-π*. In the 5-membered ring of furanones the contribution of this mode is limited and the pyramidalization in the C4 position also contributes to the stabilization. The contribution of each stabilization mode is characterized by the dihedral angles and the Mulliken atomic spin densities. The substituent effect on the pyramidalization and the spin density distribution in the C4 and in the C5 position are reported. Depending on the substitution in the C4 position, the orientation of the pyramidalization is either favored syn or anti with respect of the hydroxyl substituent in the C5 position.

Published
2016
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4. Phototransformation of tetrazoline oxime ethers – part 2: theoretical investigation

Author

Jean-Pierre Vors, Pascal de Sainte Claire, Maxime Fréneau, Norbert Hoffmann, Pierre Genix, Claire Richard, Institut de Chimie de Clermont-Ferrand (ICCF), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-SIGMA Clermont (SIGMA Clermont)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut de Chimie Moléculaire de Reims - UMR 7312 (ICMR), SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Bayer S.A.S, Université de Reims Champagne-Ardenne (URCA)-Institut de Chimie du CNRS (INC)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), Université de Reims Champagne-Ardenne (URCA)-Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)-SFR Condorcet, and Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Photoisomerization, 010405 organic chemistry, Chemistry, General Chemical Engineering, Substituent, General Chemistry, 010402 general chemistry, Photochemistry, 01 natural sciences, 0104 chemical sciences, chemistry.chemical_compound, Intersystem crossing, Excited state, [CHIM]Chemical Sciences, Singlet state, Photodegradation, Ground state, Conformational isomerism
Abstract

International audience; The competitive photoisomerization and photodegradation reactions of a tetrazoline oxime ether showing important fungicidal activity are investigated by Time Dependent-Density Functional Theory (TD-DFT) and Complete Active Space Self-Consistent Field (CASSCF) calculations of ground state and excited state (singlet, S and triplet, T) potential energy surfaces. Two key experimental results reported previously are explained in this study: (1) why only E isomers undergo N–O bond scission and photodegradation and (2) what is the mechanism for deactivation of the Z isomers. In addition, the reactive pathway that involves intersystem crossing is shown to be competitive with reactions in the singlet state. Our results demonstrate that the photoreactivity (photodegradation or photoisomerization) of the eight conformers studied here is clearly related to the differences between the respective electronic configurations of the lowest singlet excited state. It is shown that the addition of a bulky substituent on the pyridyl group prevents E isomers from being photodegraded.

Published
2016
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5. Phototransformation of tetrazoline oxime ethers: photoisomerization vs. photodegradation

Author

Maxime Fréneau, Pascal de Sainte Claire, Michel Euvrard, Jean-Pierre Vors, Julie Geist, Claire Richard, Norbert Hoffmann, Institut de Chimie de Clermont-Ferrand (ICCF), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-SIGMA Clermont (SIGMA Clermont)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut de Chimie Moléculaire de Reims - UMR 7312 (ICMR), Université de Reims Champagne-Ardenne (URCA)-Institut de Chimie du CNRS (INC)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), Université de Reims Champagne-Ardenne (URCA)-Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)-SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS), Bayer S.A.S, SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), and Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)

Subjects
chemistry.chemical_classification, Photoisomerization, 010405 organic chemistry, General Chemical Engineering, General Chemistry, 010402 general chemistry, Photochemistry, Oxime, 01 natural sciences, Aldehyde, 0104 chemical sciences, chemistry.chemical_compound, chemistry, Solar light, Alkoxyl radicals, [CHIM]Chemical Sciences, Photodegradation, Green house
Abstract

International audience; Fungicides showing potent biological activity in green house may have poor activity in the field due to fast photodegradation. This is the case of tetrazoline oxime ethers 1 and 2, active in the Z form, on which very little is known. A comprehensive study was therefore conducted to understand the photochemical behaviour of these compounds. It could be firmly demonstrated that both photoisomerization Z ⇄ E and photodegradation occur, and that interestingly photodegradation only takes place from E forms. Quantum yields of photoisomerization lay within the range 0.38–0.48 and those of E photodegradation in the range 0.06–0.11. During the reaction, the non-fungicidal E forms become the major isomers due to their lower solar light absorptivity than Z forms. The analytical study showed that photodegradation involves the cleavage of the N–O bond and allowed the identification of photoproducts arising from the rearrangement of the iminyl and alkoxyl radicals. Moreover, the proposed mechanism of alkoxyl radical oxidation into corresponding aldehyde and acid was elucidated using a computational study. This fundamental investigation fully explains the fast loss of the fungicidal activity of tetrazoline oxime ethers 1 and 2 in the field.

Published
2016
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