- Switchable asymmetric bio-epoxidation of α,β-unsaturated ketones
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Efficient asymmetric bio-epoxidation of electron-deficient α,β-unsaturated ketones was realized via a tandem reduction-epoxidation-dehydrogenation cascade, which proceeds in a switchable manner to afford either chiral epoxy ketones or allylic epoxy alcoho
- Liu, Yu-Chang,Wu, Zhong-Liu
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supporting information
p. 1158 - 1161
(2016/01/15)
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- Asymmetric epoxidation of styrene derivatives by styrene monooxygenase from Pseudomonas sp. LQ26: Effects of α- And β-substituents
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Recombinant Escherichia coli expressing a styrene monooxygenase, StyAB2, from Pseudomonas sp. LQ26 was applied to synthesize a range of chiral epoxides from conjugated styrene derivatives with excellent (>99%) enantioselectivity in most cases. The substrate preference was studied with a special focus on the steric effect of α- and β-substituents.
- Lin, Hui,Liu, Yan,Wu, Zhong-Liu
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experimental part
p. 134 - 137
(2011/04/27)
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- Enantioselective epoxidation with chiral MnIII(salen) catalysts: Kinetic resolution of aryl-substituted allylic alcohols
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A set of aryl-substituted allylic alcohols rac-2 has been epoxidized by chiral Mn(salen*) complexes 1 as the catalyst and iodosyl benzene (PhIO) as the oxygen source. Whereas one enantiomer of the allylic alcohol 2 is preferentially epoxidized to give the threoor cis-epoxy alcohol 3 (up to 80% ee) as the main product (dr up to >95:5), the other enantiomer of 2 is enriched (up to 53% ee). In the case of 1,1-dimethyl-1,2-dihydronaphthalen-2-ol (2c), the CH oxidation to the enone 4c proceeds enantioselectively and competes with the epoxidation. The absolute configurations of the allylic alcohols 2 and their epoxides 3 have been determined by chemical correlation or CD spectroscopy. The observed diastereo- and enantioselectivities in the epoxidation reactions are rationalized in terms of a beneficial interplay between the hydroxy-directing effect and the attack along the Katsuki trajectory.
- Adam,Humpf,Roschmann,Saha-Moeller
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p. 5796 - 5800
(2007/10/03)
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- A highly chemoselective oxidation of alcohols to carbonyl products with iodosobenzene diacetate mediated by chromium(III)(salen) complexes: Synthetic and mechanistic aspects
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The catalytic oxidation of the allylic alcohols 1d-n with iodosobenzene diacetate, mediated by the [CrIII(salen)]X complex, affords the respective enones in excellent chemoselectivity for Cl- as counterion [complex A(Cl)], while for the counterions TfO- [complex A(TfO)] and PF6- [complex A(PF6)] nearly equal amounts of enone and epoxide are observed. This counterion-dependent oxidation of allylic alcohols by CrIII(salen) complexes is rationalized in terms of Lewis acid catalysis by the complex A(Cl) and redox catalysis for A(TfO) and A(PF6).
- Adam, Waldemar,Hajra, Saumen,Herderich, Markus,Saha-M?ller, Chantu R.
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p. 2773 - 2776
(2007/10/03)
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- Carbodiimide-Promoted Olefin Epoxidation with Aqueous Hydrogen Peroxide
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Commercially available carbodiimides in hydroxylic solvents containing hydrogen peroxide with mildly basic or acidic catalysts have been found to promote the epoxidation of olefins. A commercially available 30% aqueous solution of hydrogen peroxide serves as the oxidant for this process. The presumed reactive species is a peroxyisourea generated in situ by the addition of hydrogen peroxide to the carbodiimide.
- Majetich, George,Hicks, Rodgers,Sun, Guang-Ri,McGill, Patrick
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p. 2564 - 2573
(2007/10/03)
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- Modified Borohydride Agents, 1-Benzyl-4-aza-1-azoniabicyclooctane Tetrahydroborate (BAAOTB) versus Tetrabutylammonium Tetrahydroborate (TBATB). Efficient, Selective, and Versatile Reducing Agents
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1-Benzyl-4-aza-1-azoniabicyclooctane tetrahydroborate (BAAOTB) and tetrabutylammonium tetrahydroborate (TBATB) are used for the selective reductions of aldehydes, ketones, α,β-unsaturated carbonyl compounds, acid chlorides, azides, epoxides, and disulfides in t-BuOH and hexane/chloroform.ABBOAB with its rigid and bulky structure reacts more selectively than its analogue TBATB.
- Firouzabadi, Habib,Afsharifar, Gholam Reza
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p. 2595 - 2602
(2007/10/03)
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- Novel Synthesis of syn-α,β-Epoxy Alcohols by Diastereoselective Carbonyl Reduction of α,β-Epoxy Ketones
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A novel tin hydride reagent, Bu3SnH-Bu4NCN, reduced α,β-epoxy ketones to the corresponding syn-α,β-epoxy alcohols in high diastereoselectivities.
- Kawakami, Takayo,Shibata, Ikuya,Baba, Akio,Matsuda, Haruo,Sonoda, Noboru
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p. 8625 - 8626
(2007/10/02)
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- Organoaluminum-catalyzed rearrangement of epoxides a facile route to the synthesis of optically active β-siloxy aldehydes
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A new, stereocontrolled rearrangement of epoxy silyl ethers leading to β-siloxy aldehydes has been effected with stoichiometric use of exceptionally bulky, oxygenophilic methylaluminum bis(4-bromo-2,6-di-trert-butylphenoxide) (MABR) under mild conditions. Used in combination with the Sharpless asymmetric epoxidation of allylic alcohols, this rearrangement represents a new approach to the synthesis of various optically active β-hydroxy aldehydes, useful intermediates in natural product synthesis. The modified organoaluminum reagent, MABR is also applicable to the transformation of a variety of simple epoxides to carbonyl compounds with high efficiency and selectivity. Further, the catalytic version for the rearrangement of epoxy silyl ethers as well as simple epoxides has been newly devised. The scope and limitation of this catalytic method has been clarified with various epoxy substrates.
- Maruoka, Keiji,Ooi, Takashi,Nagahara, Shigeru,Yamamoto, Hisashi
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p. 6983 - 6998
(2007/10/02)
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- Cleavage of 2,3-Epoxyalkylhalides by the Sonochemical Zinc-Copper Couple
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2,3-Epoxyalkylhalides are readily transformed into allylic alcohols when sonicated in the presence of a zinc-copper couple in aqueous ethanol.
- Sarandeses, Luis A.,Mourino, Antonio,Luche, Jean-Louis
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p. 818 - 820
(2007/10/02)
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- A Novel Probe for Free Radicals featuring Epoxide Cleavage
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This paper describes the identification of carbon-carbon bond cleavage within a defined range of epoxides as being a reaction type which is specifically diagnostic of free radicals adjacent to the epoxide.The speed of the epoxide cleavage is greater than
- Dickinson, Julia M.,Murphy, John A.,Patterson, Christopher W.,Wooster, Nicholas F.
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p. 1179 - 1184
(2007/10/02)
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- Hydrogenolysis of α,β-Epoxyketone and Ester to Aldol in Pd(0)/HCOOH/Et3N and H2/Pd/C Reduction Media
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Hydrogenation of α,β-epoxycarbonyl compounds by using several catalysts and hydride sources was studied to obtain the corresponding β-hydroxy substrates.
- Torii, Sigeru,Okumoto, Hiroshi,Nakayasu, Seizo,Kotani, Takayuki
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p. 1975 - 1978
(2007/10/02)
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