- Asymmetric total synthesis of a beer-aroma constituent based on enantioconvergent biocatalytic hydrolysis of trisubstituted epoxides
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A short asymmetric total synthesis of the plant constituent myrcenediol [(R)-1], and (S)-7,7-dimethyl-6,8-dioxabicyclo [3.2.1]octane (2), which is a volatile constituent of the aroma of beer was accomplished via a chemoenzymatic protocol. The key step consisted of a biocatalytic hydrolysis of trisubstituted epoxides bearing olefinic side chains which proceeded in an enantioconvergent fashion, i.e., a single enantiomeric vic-diol was obtained from the racemate in up to 91% ee and 92% isolated yield.
- Steinreiber,Mayer,Faber
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- Regioselectivity and diasteroselectivity in Pt(II)-mediated "green" catalytic epoxidation of terminal alkenes with hydrogen peroxide: Mechanistic insight into a peculiar substrate selectivity
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Recently developed electron-poor Pt(II) catalyst 1 with the "green" oxidant 35% hydrogen peroxide displays high activity and complete substrate selectivity in the epoxidation of terminal alkenes because of stringent steric and electronic requirements. In the presence of isolated dienes bearing terminal and internal double bonds, epoxidation is completely regioselective toward the production of terminal epoxides. Insight into the mechanism is gained by means of a reaction progress kinetic analysis approach that underlines the peculiar role of 1 in activating both the alkene and H 2O2 in the rate-determining step providing a rare example of nucleophilic oxidation of alkenes by H2O2.
- Colladon, Marco,Scarso, Alessandro,Sgarbossa, Paolo,Michelin, Rino A.,Strukul, Giorgio
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p. 7680 - 7689
(2008/02/05)
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- Oxidation of alkenes by oxodiperoxomolybdenum: Trialkyl(aryl)phosphine oxide complexes
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Catalytic amounts of short-chain (2-4 carbons) trialkylphosphine oxide ligands and MoO5 have been shown to efficiently convert di- and higher substituted alkenes to the corresponding epoxides using a biphasic system with either 30% hydrogen peroxide or 70% TBHP acting as the stoichiometric oxidant. Georg Thieme Verlag Stuttgart.
- Kiraz, Christine I. Altinis,Mora, Luis,Jimenez, Leslie S.
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- Olefin epoxidation with hydrogen peroxide catalyzed by lacunary polyoxometalate [γ-SiW10O34(H2O) 2]4-
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The tetra-n-butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA]4[γ-SiW10O34-(H 2O)2] (I) catalyzes the oxygen-transfer reactions of olefins, allylic alcohols, and sulfides with 30% aqueous hydrogen peroxide. The negative Hammett ρ+ (-0.99) for the competitive oxidation of p-substituted styrenes and the low value of (nucleophilic oxidation)/(total oxidation), Xso = 0.04, for I-catalyzed oxidation of thianthrene 5-oxide (SSO) reveals that a strongly electrophilic oxidant species is formed on I. The preferential formation of trans-spoxide during epoxidation of 3-methyl-1-cyclohexene demonstrates the steric constraints of the active site of I. The I-catalyzed epoxidation proceeds with an induction period that disappears upon treatment of I with hydrogen peroxide. 29Si and 183W NMR spectroscopy and CSI mass spectrometry show that reaction of I with excess hydrogen peroxide leads to fast formation of a diperoxo species, [TBA]4[γ-SiW10O32(O2) 2] (II), with retention of a γ-Keggin type structure. Whereas the isolated compound II is inactive for stoichiometric epoxidation of cyclooctene, epoxidation with II does proceed in the presence of hydrogen peroxide. The reaction of II with hydrogen peroxide would form a reactive species (III), and this step corresponds to the induction period observed in the catalytic epoxidation. The steric and electronic characters of III are the same as those for the catalytic epoxidation by I. Kinetic, spectroscopic, and mechanistic investigations show that the present epoxidation proceeds via III.
- Kamata, Keigo,Kotani, Miyuki,Yamaguchi, Kazuya,Hikichi, Shiro,Mizuno, Noritaka
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p. 639 - 648
(2007/10/03)
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- Titanium-catalyzed asymmetric epoxidation of non-activated olefins with hydrogen peroxide
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A greener oxidation: A titanium(salalen) complex catalyzes the asymmetric epoxidation of aliphatic (non-activated) olefins using aqueous hydrogen peroxide as the oxidant. Reactions with aliphatic terminal and Z olefins furnish the corresponding epoxides in good yields with high enantioselectivities of up to 97% ee.
- Sawada, Yuji,Matsumoto, Kazuhiro,Katsuki, Tsutomu
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p. 4559 - 4561
(2008/09/16)
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- Polyoxovanadometalate-catalyzed selective epoxidation of alkenes with hydrogen peroxide
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The bis(μ-hydroxo)-bridged dioxovanadium site in [γ-1,2-H 2SiV2W10O40]4 catalyzes the epoxidation of alkenes in the presence of only one equivalent of H 2O2 with a high yield of epoxide, high efficiency of H2O2 utilization, unusual regioselectivity, and unprecedented diastereoselectivity (see picture). (Chemical Equation Presented)
- Nakagawa, Yoshinao,Kamata, Keigo,Kotani, Miyuki,Yamaguchi, Kazuya,Mizuno, Noritaka
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p. 5136 - 5141
(2007/10/03)
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- Regioselective alkene carbon-carbon bond cleavage to aldehydes and chemoselective alcohol oxidation of allylic alcohols with hydrogen peroxide catalyzed by [cis-Ru(II)(dmp)2(H2O)2] 2+ (dmp = 2,9-dimethylphenanthroline)
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(Chemical Equation Presented) [cis-Ru(II)(dmp)2(H 2O)2]2+ (dmp = 2,9-dimethylphenanthroline) was found to be a selective oxidation catalyst using hydrogen peroxide as oxidant. Thus, primary alkenes were very efficiently oxidized via direct carbon-carbon bond cleavage to the corresponding aldehydes as an alternative to ozonolysis. Secondary alkenes were much less reactive, leading to regioselective oxidation of substrates such as 4-vinylcyclohexene and 7-methyl-1,6-octadiene at the terminal position. Primary allylic alcohols were chemoselectively oxidized to the corresponding allylic aldehydes, e.g., geraniol to citral.
- Kogan, Vladimir,Quintal, Miriam M.,Neumann, Ronny
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p. 5039 - 5042
(2007/10/03)
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- Chemoselective epoxidation of dienes using polymer-supported manganese porphyrin catalysts
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Manganese porphyrin catalysts supported on different polymer resins were assessed in the selective epoxidation of three dienes. The recyclability of the catalysts was examined.
- Brulé, Emile,De Miguel, Yolanda R.,Hii, King Kuok
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p. 5913 - 5918
(2007/10/03)
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- Efficient, regioselective epoxidation of dienes with hydrogen peroxide catalyzed by [γ-SiW10O34(H2O) 2]4-
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A divacant, lacunary, Keggin-type silicotungstate, [γ-SiW 10O34(H2O)2]4-, exhibits high catalytic performance for the epoxidation of various nonconjugated dienes using hydrogen peroxide under mild conditions, high regioselectivity to the more accessible double bonds, and high efficiency of hydrogen peroxide utilization. The high regioselectivity for the [γ-SiW10O34(H 2O)2]4--catalyzed epoxidation would be caused by the steric hindrance of the active site.
- Kamata, Keigo,Nakagawa, Yoshinao,Yamaguchi, Kazuya,Mizuno, Noritaka
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p. 224 - 228
(2007/10/03)
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- Fluorinated alcohols: Effective solvents for uncatalysed epoxidations with aqueous hydrogen peroxide
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Buffered aqueous hydrogen peroxide in combination with fluorinated alcohols (trifluoroethanol at reflux temperature or hexafluoro-2-propanol at room temperature) oxidises a variety of alkenes to the corresponding epoxides in high rates and fairly high yields, without the need for any catalyst.
- Van Vliet,Arends,Sheldon
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p. 248 - 250
(2007/10/03)
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- Hexafluoroacetone in hexafluoro-2-propanol: A highly active medium for epoxidation with aqueous hydrogen peroxide
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The combination of hexafluoro-2-propanol and catalytic amounts of hexafluoroacetone gives a versatile medium for epoxidation of a wide range of alkenes with aqueous hydrogen peroxide.
- Van Vliet,Arends,Sheldon
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p. 1305 - 1307
(2007/10/03)
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- Metal-Catalyzed Organic Photoreactions. Chemo- and Regioselectivities in the CuCl2-Induced Photooxidation of Olefins.
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Copper(II) chloride induced the chemo and regioselective chlorohydroperoxidation, as well as the site-selective chlorination of olefins, under photooxygenation conditions.
- Sato, Tadashi,Yonemochi, Shin-ichi
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p. 7375 - 7384
(2007/10/02)
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