- Titanium cis-1,2-Diaminocyclohexane Salalen Catalysts of Outstanding Activity and Enantioselectivity for the Asymmetric Epoxidation of Nonconjugated Terminal Olefins with Hydrogen Peroxide
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We report a new and readily accessible class of titanium salalen complexes derived from cis-1,2-diaminocyclohexane (cis-DACH) and fluorinated salicylic aldehyde derivatives. With aqueous hydrogen peroxide as the oxidant, these complexes catalyze the epoxidation of terminal, nonconjugated olefins in high yields with high enantioselectivities. We furthermore discovered that the addition of certain acidic or basic co-catalysts significantly accelerated the epoxidation. For example, in the presence of 1 mol % Ti catalyst and 1 mol % pentafluorobenzoic acid, 1-octene epoxidation (95 % ee) was completed at room temperature within 8 h. The catalytic process was compatible with many functional groups (e.g., ethers, esters, halides, nitriles, and nitro groups), whereas free hydroxy groups appeared to slow down the reaction to some extent. Catalyst recycling was possible.
- Lansing, Markus,Engler, Hauke,Leuther, Tobias M.,Neud?rfl, J?rg-M.,Berkessel, Albrecht
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p. 3706 - 3709
(2016/12/24)
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- Synthesis of a putative advanced intermediate en route to elisabethin A
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The first generation synthesis of an advanced intermediate en route to elisabethin A is described.
- Steiner, Sebastian,G?rtner, Peter,Enev, Valentin S.
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p. 4536 - 4542
(2016/07/07)
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- Azidolysis of epoxides catalysed by the halohydrin dehalogenase from Arthrobacter sp. AD2 and a mutant with enhanced enantioselectivity: an (S)-selective HHDH
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Halohydrin dehalogenase from Arthrobacter sp. AD2 catalysed azidolysis of epoxides with high regioselectivity and low to moderate (S)-enantioselectivity (E?=?1–16). Mutation of the asparagine 178 to alanine (N178A) showed increased enantioselectivity towards styrene oxide derivatives and glycidyl ethers. Conversion of aromatic epoxides was catalysed by HheA-N178A with complete enantioselectivity, however the regioselectivity was reduced. As a result of the enzyme-catalysed reaction, enantiomerically pure (S)-β-azido alcohols and (R)-α-azido alcohols (ee???99%) were obtained.
- Mikleu?evi?, Ana,Primo?i?, Ines,Hrenar, Tomica,Salopek-Sondi, Branka,Tang, Lixia,Elenkov, Maja Majeri?
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p. 930 - 935
(2016/09/13)
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- Heterobimetallic dual-catalyst systems for the hydrolytic kinetic resolution of terminal epoxides
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A heterobimetallic dual-catalyst system based on the preparation and use of various salen complexes has been developed for the hydrolytic kinetic resolution (HKR) of terminal epoxides. A combination of cobalt-salen and manganese-salen complexes, generated from ligands with the same configuration possessing thiophene or pyrrole moieties, produced indeed highly selective catalysts for the hydrolysis of epibromohydrin. This effect could also be extended to other terminal epoxides and to the more challenging ring opening of cyclohexene oxide. Kinetic studies indicated that only one CoIII salen complex was involved in the rate-determining step, which supported a heterobimetallic highly enantioselective pathway based on the crucial existence of in situ generated CoIII-OH species, previously postulated in the literature. The beneficial effect of the presence of additional Mn-complexes was ascribed to the inhibition of the alternative less enantioselective monometallic reaction pathway by epoxide activation.
- Hong, Xiang,Mellah, Mohamed,Schulz, Emmanuelle
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p. 2608 - 2617
(2014/07/22)
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- Shell cross-linked micelle-based nanoreactors for the substrate-selective hydrolytic kinetic resolution of epoxides
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Shell cross-linked micelles (SCMs) containing Co(III)-salen cores were prepared from amphiphilic poly(2-oxazoline) triblock copolymers. The catalytic activity of these nanoreactors for the hydrolytic kinetic resolution of various terminal epoxides was investigated. The SCM catalysts showed high catalytic efficiency and, more significantly, substrate selectivity based on the hydrophobic nature of the epoxide. Moreover, because of the nanoscale particle size and the high stability, the catalyst could be recovered easily by ultrafiltration and reused with high activity for eight cycles.
- Liu, Yu,Wang, Yu,Wang, Yufeng,Lu, Jie,Pinon, Victor,Weck, Marcus
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supporting information; experimental part
p. 14260 - 14263
(2011/11/05)
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- Self-assembly approach toward chiral bimetallic catalysts: Bis-urea-functionalized (Salen)cobalt complexes for the hydrolytic kinetic resolution of epoxides
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A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13atimes) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)CoIII catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05amol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by 1HaNMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis.
- Park, Jongwoo,Lang, Kai,Abboud, Khalil A.,Hong, Sukwon
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supporting information; experimental part
p. 2236 - 2245
(2011/03/22)
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- ISOSELECTIVE POLYMERIZATION OF EPOXIDES
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The present invention provides novel bimetallic complexes and methods of using the same in the isoselective polymerization of epoxides. The invention also provides methods of kinetic resolution of epoxides. The invention further provides polyethers with high enantiomeric excess that are useful in applications ranging from consumer goods to materials.
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Page/Page column 69; 73
(2009/04/25)
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- Engineering polymer-enhanced bimetallic cooperative interactions in the hydrolytic kinetic resolution of epoxides
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Through systematic variations of the length of oligo(ethylene glycol)-based linkers and the catalyst density of poly(styrene)-supported cobalt-salen catalysts, we have elucidated an optimal catalyst flexibility and density of polymeric Co-salen catalysts for the hydrolytic kinetic resolution (HKR) of racemic terminal epoxides that follows a bimetallic cooperative pathway. The optimized polymeric catalyst brings the two cooperative Co-salen units to a favorable proximity efficiently and hence displays significantly improved catalytic performance in the HKR compared with its monomeric small molecule analogue. Complex Co(5b), representing the most active poly(styrene)-supported HKR catalyst known so far, can effect the resolution of a variety of epoxides to reach ≥ 98 % ee in 6-24 h with a low cobalt loading of 0.01-0.1 mol%.
- Zheng, Xiaolai,Jones, Christopher W.,Weck, Marcus
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supporting information; experimental part
p. 255 - 261
(2009/04/08)
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- Catalytic dehydrative allylation of alcohols
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(Chemical Equation Presented) An environmentally benign synthesis of allyl ethers has been developed which can be applied to a highly chemoselective protection of hydroxyl groups. A highly efficient [CpRu]-2-quinolinecarboxylic acid (L) catalytic system was successfully employed for the dehydrative allylation of various alcohols without additional activators and solvent (see scheme; R = alkyl, aryl, multifunctional alkyl, Cp = C5H 5).
- Saburi, Hajime,Tanaka, Shinji,Kitamura, Masato
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p. 1730 - 1732
(2007/10/03)
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- New oligomeric catalyst for the hydrolytic kinetic resolution of terminal epoxides under solvent-free conditions
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The solvent-free hydrolytic kinetic resolution of terminal epoxides catalyzed by a new oligomeric (salen)Co complex 2 is described. Extremely low loadings of catalyst were used to provide all epoxides examined in good yields and >99% ee under ambient conditions within 24 h.
- White, David E.,Jacobsen, Eric N.
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p. 3633 - 3638
(2007/10/03)
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- Asymmetric epoxidation of allyl alcohol derivatives by ω-hydroxylase from Pseudomonas oleovorans
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This paper described the application of non-heme monooxygenase system from Pseudomonas oleovorans to the syntheses of chiral 3-(benzyloxy)-, 3-(allyloxy)-, 3-(butyloxy)- and 3-(aryloxy)-1,2-epoxypropanes (6) from their corresponding allyl alcohol derivatives.The epoxides were determined to be R forms with good enantiomeric excess.The specificities of the enzymatic epoxidation of olefines and hydroxylation of the radical probe trans-2-phenyl-1-methylcyclopropane were discussed with regard to the reaction mechanism.
- Fu, Hong,Shen, Gwo-Jenn,Wong, Chi-Huey
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p. 167 - 170
(2007/10/02)
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- Enzymes in Organic Synthesis: Synthesis of Highly Enantiomerically Pure 1,2-Epoxy Aldehydes, Epoxy Alcohols, Thiirane, Aziridine, and Glyceraldehyde 3-Phosphate
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This paper describes a chemoenzymatic procedure for the synthesis of (R)- and (S)-glycidaldehyde diethyl acetal (4 and 5). 2-Acetoxy-3-chloropropanal diethyl acetal (1c) was enantioselectively hydrolyzed by LP-80 lipase to give (S)-3-chloro-2-hydroxypropanal diethyl acetal (2c) and the unreacted acetate (3c), both in >95percent calculated yield and >98percent ee.Both products were subsequently converted to epoxides 4 and 5, respectively.Resolutions of 2-acetoxy-1-(benzyloxy)-3-chloropropane (11a) and 3-(allyloxy)-2-acetoxypropyl p-toluenesulfonate (14b) were similarly carried out to give the corresponding optically active 2-hydroxy and 2-acetoxy derivatives in 90percent and >95percent ee.These products were subsequently converted to the corresponding 1,2-epoxides.Nucleophilic opening of epoxide 4 was exemplified by the syntheses of (R)-3-azido-2-hydroxypropanal and D-glyceraldehyde 3-phosphate.Conversion of the chiral epoxides to thiirane and aziridine was also described.
- Pederson, Richard L.,Liu, Kevin K.-C.,Rutan, James F.,Chen, Lihren,Wong, Chi-Huey
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p. 4897 - 4901
(2007/10/02)
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- The Chemistry of L-Ascorbic and D-Isoascorbic Acids. 2. R and S Glyceraldehydes from a Common Intermediate
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(R)- and (S)-glyceraldehyde and glycerol derivatives have been prepared from (2R,3S)-1,2-O-isopropylidenebutane-1,2,3,4-tetrol. (2R,3S)- and (2S,3S)-1,2-O-benzylidenebutane-1,2,3,4-tetrol have been prepared and cleaved to give (R)- and (S)-1,2-O-benzylideneglyceraldehydes and -glycerols.The conservation of chirality and conversion to PAF analogues are also demonstrated.
- Mikkilineni, Amarendra B.,Kumar, Praveen,Abushanab, Elie
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p. 6005 - 6009
(2007/10/02)
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- Stereoselective Synthesis of 1- and 2-O-α-D-Cellotriosyl-3-deoxy-2(R)- and 2(S)-glycerols Related to Rhynchosporoside
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The stereoselective synthesis of 1- and 2-O-α-D-cellotriosyl-3-deoxy-2(R)- and 2(S)-glycerols, which determined the structure of rhynchosporoside produced by Rhynchosporium secalis, and their phytotoxicity toward the host plant (Hordeum vulgare) are described in detail.
- Sugawara, Fumio,Nakayama, Haruhiko,Stroebel, Gary A.,Ogawa, Tomoya
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p. 2261 - 2272
(2007/10/02)
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