- Novel catalytic hydrogenolysis of trimethylsilyl enol ethers by the use of an acidic ruthenium dihydrogen complex
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The heterolytic cleavage of H2 is the key to the novel catalytic hydrogenolysis of trimethylsilyl enol ethers catalyzed by [RuCl(η2- H2)(dppe)2]OTf (dppe = 1,2-bis(diphenylphosphanyl)ethane, OTf = trifluoromethanesulfonate), which results in the formation of a ketone and Me3SiH (see scheme). In addition, the stoichiometric, ruthenium-assisted protonation of a prochiral lithium enolate with H2 gave a chiral ketone with high enantioselectivity (up to 75 % ee).
- Nishibayashi, Yoshiaki,Takei, Izuru,Hidai, Masanobu
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- Highly selective Pd@mpg-C3N4 catalyst for phenol hydrogenation in aqueous phase
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The liquid phase selective hydrogenation of phenol to cyclohexanone has been investigated over polymeric mesoporous graphitic carbon nitride (mpg-C 3N4) supported Pd catalysts (Pd@mpg-C3N 4). This Pd@mpg-C3
- Li, Yi,Xu, Xuan,Zhang, Pengfei,Gong, Yutong,Li, Haoran,Wang, Yong
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p. 10973 - 10982
(2013/09/02)
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- Novel catalytic hydrogenolysis of silyl enol ethers by the use of acidic ruthenium dihydrogen complexes
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Treatment of 1-trimethylsilyloxy-1-cyclohexene (1a) in the presence of a catalytic amount of the acidic dihydrogen complex [RuCl(η2-H2)(dppe)2]OTf (4a) [dppe=1,2-bis(diphenylphosphino)ethane, OTf=OSO2CF3] (10 mol.%) under 1 atm of H2 in anhydrous ClCD2CD2Cl at 50 °C for 8 h afforded cyclohexanone (3a) and Me3SiH in quantitative NMR yields. Silyl enol ethers such as 1-triethylsilyloxy-1-cyclohexene (1b), 1-t-butyldimethylsilyloxy-1-cyclohexene (1c), and other trimethylsilylethers (1d, 1e, and 1f) reacted similarly with H2 to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H2 to the trimethylsilyl enol ethers (1a and 1d-1f) was confirmed by the experiments employing D2 gas, where α-monodeuterated ketones (3a′ and 3d′-3f′) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H2 by employing [RuCl(η2-H2) ((S)-BINAP)2]OTf (4e) [BINAP=2,2′-bis (diphenylphosphino)-1,1′-binaphthyl] and [RuCl(η2-H2)((R, R)-CHIRAPHOS)2]OTf (4f) [CHIRAPHOS=2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe)2] (5a) with one equivalent of Me3SiOTf under 1 atm of H2 produced rapidly 4a, concurrent with the formation of Me3SiH. Based on these studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the coordinated H2 on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and Me3SiOTf, and the subsequent reaction of the resultant complex 5a with Me3SiOTf under 1 atm of H2 to regenerate the original dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at -78 °C in CH2Cl2 under 1 atm of H2 afforded 2-methyl-1-tetralone (3e) with 75% ee (S) in >95% yield, together with the formation of [RuHCl((S)-BINAP)2] (5e).
- Takei, Izuru,Nishibayashi, Yoshiaki,Ishii, Youichi,Mizobe, Yasushi,Uemura, Sakae,Hidai, Masanobu
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- Highly efficient antibody-catalyzed deuteration of carbonyl compounds
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Antibody 38C2 efficiently catalyzes deuterium-exchange reactions at the α position of a variety of ketones and aldehydes, including substrates that have a variety of sensitive functional groups. In addition to the regio- and chemoselectivity of these reactions, the catalytic rates (kcat) and rate-enhancement values (kcat/kun) are among the highest values ever observed with catalytic antibodies. Comparison of the substrate range of the catalytic antibody with highly evolved aldolase enzymes, such as rabbit-muscle aldolase, highlights the much broader practical scope of the antibody, which accepts a wide range of substrates. The hydrogen-exchange reaction was used for calibration and mapping of the antibody active site. Isotope-exchange experiments with cycloheptanone reveal that the formation of the Schiff base species (as concluded from the 16O/18O exchange rate at the carbonyl oxygen) is much faster than the formation of the enamine intermediate (as concluded from the H/D exchange rate), and both steps are faster than the antibody-catalyzed aldol addition reaction.
- Shulman, Avidor,Sitry, Danielle,Shulman, Hagit,Keinan, Ehud
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p. 229 - 239
(2007/10/03)
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- Dehalogenation of α-Halo Carbonyl Compounds by a New Efficient Reagent, Triphenylphosphonium Iodide
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Triphenylphosphonium iodide, Ph3PHI, was found to be an efficient reagent for the dehalogenation of α-halo carbonyl compounds. α-Halo esters, which were difficult to be reduced with Me3SiCl/NaI reagent, was smoothly debromiated by Ph3PHI.Treatment of α-halocarbonyl compounds with Ph3PDI produced the corresponding α-deuterated compounds.
- Kamiya, Naoshi,Tanmatu, Hiroshi,Ishii, Yasutaka
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p. 293 - 296
(2007/10/02)
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