- Photooxygenation od 1,ω-Bis(diarylethenyl)alkanes via Photoinduced Electron-Transfer: Formation of 1,4-Radical Cations and Its Trapping by Molecular Dioxygen
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The 9,10-dicyanoanthracene (DCA)-sensitized photooxygenation of 1,ω-bis(diarylethenyl)alkanes (Ar2C=CH(CH2)nCH=Ar2) was studied.The photooxygenation of the alkadienes in acetonitrile afforded bicyclic peroxides when Ar = 4-CH3OC6H4, n = 3 and 4.When Ar = 4-CH3OC6H4, n = 2, 5, 8 or Ar = C6H5, n = 3, the photooxygenation did not afford bicyclic peroxides, but gave diaryl ketones.Laser flash photolysis studies indicated that the photooxygenation is initiated by a one-electron transfer from the alkadienes to 1DCA* and proceeds via 1,4-radical cations that are generated by an intramolecular cyclization between an ethenyl moiety and a radical cation of another ethenyl moiety.
- Mizuno, Kazuhiko,Tamai, Toshiyuki,Hashida, Isao,Otsuji, Yoshio,Kuriyama, Yasunao,Tokumaru, Katsumi
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- Photooxygenation of 1,ω-Bis(diarylethenyl)alkanes via Photoinduced Electron Transfer: Formation of Bicyclic Peroxides
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The 9,10-dicyanoanthracene (DCA)-sensitized photooxygenation of Ar2C=CH(CH2)nCH=CAr2 in acetonitrile was studied.When Ar = 4-CH3OC6H4, n = 3 and 4, bicyclic peroxides were obtained via 1,4 radical cations that are generated by intramolecular interaction between two ethenyl moieties of the alkadienes.
- Tamai, Toshiyuki,Mizuno, Kazuhiko,Hashida, Isao,Otsuji, Yoshio
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- Benzyl C–O and C–N Bond Construction via C–C Bond Dissociation of Oxime Ester under Visible Light Irradiation
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A photoredox benzyl activation was developed via formidable C(sp3)–C(sp3) bond dissociation of 1-aryl acetone oxime esters, which were easily prepared from benzyl ketones. Further coupling with O- and N- nucleophiles successfully forged important benzyl ether and amines derivatives in one pot. In this process, different substitutions on oxime esters were found compatible and various primary and secondary alcohols and amines, as well as amides showed good performance as nucleophiles. Mechanistic studies by control experiments, electrochemical measurements and in-situ NMR spectra proposed a N–O bond interruption/C–C bond fragmentation/oxidation sequence to provide the key cation intermediate for the next electrophilic SN process. The features of mild condition, short reaction time and broad substrate scope made this new strategy much promising in the transformation of benzyl compounds, which might be valuable in last-stage functionalizations.
- Fan, Xiuwei,Lei, Tao,Liu, Zan,Yang, Xiu-Long,Cheng, Yuan-Yuan,Liang, Ge,Chen, Bin,Tung, Chen-Ho,Wu, Li-Zhu
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p. 1551 - 1558
(2019/09/09)
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- Enantioselective protonation of radical anion intermediates in photoallylation and photoreduction reactions of 3,3-diaryl-1,1-dicyano-2-methylprop-1-ene with allyltrimethylsilane
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Photoreactions of acetonitrile solutions of 3,3-diaryl-1,1-dicyano-2-methylprop-1-enes (1a–c) with allyltrimethylsilane (2) in the presence of phenanthrene as a photoredox catalyst and acetic acid as a proton source formed photoallylation (3) and photored
- Maeda, Hajime,Iida, Masayuki,Ogawa, Daisuke,Mizuno, Kazuhiko
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- Palladium-catalyzed amination of aromatic C-H bonds with oxime esters
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"Chemical equation presented" We report a conceptually new approach to the direct amination of aromatic C-H bonds. In this process, an oxime ester function reacts with an aromatic C-H bond under redox-neutral conditions to form, in the case studied, an indole product. These reactions occur with relatively low catalyst loading (1 mol %) by a mechanism that appears to involve an unusual initial oxidative addition of an N-O bond to a Pd(0) species. The Pd(II) complex from oxidative addition of the N-X bond has been isolated for the first time, and evidence for the intermediacy of such oxidative addition products in the catalytic reaction has been gained.
- Tan, Yichen,Hartwig, John F.
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supporting information; experimental part
p. 3676 - 3677
(2010/05/15)
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- Activation conditions play a key role in the activity of zeolite CaY: NMR and product studies of Bronsted acidity
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CaY, activated under different conditions, was characterized with 1H, 31P, and 1H/27A] double resonance MAS NMR. The 1H MAS NMR spectra of CaY, calcined in an oven at 500 °C, shows resonances from H2O (bound to Ca2+ and the zeolite framework), CaOH+, aluminum hydroxides, silanols, and Bronsted acid sites. No evidence for Lewis acidity is observed on adsorption of trimethylphosphine, and an estimate of ≈16 Bronsted acid sites per unit cell is obtained for this sample. CaY activated in an oven at higher temperatures contains less water, but all the other species are still present. In contrast, CaY activated by slow ramping of the temperature under vacuum to 500 or 600 °C shows a much lower concentration of Bronsted acid sites (1/unit cell). Again, no evidence for Lewis acidity was observed. These NMR results have been utilized to understand the very different product distributions that are observed for reactions of 1,1- and 1,2-diarylethylenes in zeolite CaY activated in an oven (in air) and under vacuum. Samples with high concentrations of Bronsted acid sites react stoichiometrically with these sites, yielding diarylalkanes. At low concentrations, the Bronsted acid sites can act catalytically resulting in isomerization reactions.
- Kao, Hsien-Ming,Grey, Clare P.,Pitchumani, Kasi,Lakshminarasimhan,Ramamurthy
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p. 5627 - 5638
(2007/10/03)
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- CONTROL OF THE REACTIONS OF ORGANOMAGNESIUM COMPOUNDS. I. CONTROL OF THE REACTIONS OF ESTERS OF α-HYDROXY ACIDS WITH ARYLMAGNESIUM BROMIDES
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The reaction of the esters of α-hydroxy acids with arylmagnesium bromides, which usually lead to the formation of bromomagnesium glycolates, can be directed toward the formation of ketones by chemical and thermal control
- Lapkin, I. I.,Kolbina, N. M.,Tatarenko, O. I.
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p. 279 - 281
(2007/10/02)
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- Photolysis of Vinyl Halides. Preferential Formation of Vinyl Cations by Copper(II) Salts
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Photolysis of vinyl halides in the presence of copper(II) salts in a significant suppression of product formation derived from vinyl radicals.Photolysis of 1,1-diaryl-2-bromopropenes in the presence of copper(II) salts yielded no 1,1-diaryl-2-propenes.Photolysis of other vinyl halides, i.e., 1,1-diaryl-2-iodopropenes, 1,1-diaryl-2-bromoethylenes, and 1-bromo-2-(p-methoxyphenyl)ethylene, also led to a large decrease in the yields of the reduced olefins derived from the vinyl radicals.Copper(II) triflate was found to be more effective for the oxidation of vinyl radicals than copper(II) acetate.These reactions are explained by the intervention of vinylcopper intermediates and the formation of vinyl cations.
- Kitamura, Tsugio,Kobayashi, Shinjiro,Taniguchi, Hiroshi
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p. 2641 - 2645
(2007/10/02)
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