- Highly enantioselective bioinspired epoxidation of electron-deficient olefins with H2O2 on aminopyridine mn catalysts
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The asymmetric epoxidation of various electron-deficient olefins with H2O2 in the presence of a novel family of chiral bioinspired bipyrrolidine-derived aminopyridine manganese(II) complexes [LM II(OTf)2] is rep
- Ottenbacher, Roman V.,Samsonenko, Denis G.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
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p. 1599 - 1606
(2014/05/20)
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- Asymmetric synthesis of diverse glycolic acid scaffolds via dynamic kinetic resolution of α-keto esters
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The dynamic kinetic resolution of α-keto esters via asymmetric transfer hydrogenation has been developed as a technique for the highly stereoselective construction of structurally diverse β-substituted-α- hydroxy carboxylic acid derivatives. Through the development of a privileged m-terphenylsulfonamide for (arene)RuCl(monosulfonamide) complexes with a high affinity for selective α-keto ester reduction, excellent levels of chemo-, diastereo-, and enantiocontrol can be realized in the reduction of β-aryl- and β-chloro-α-keto esters.
- Steward, Kimberly M.,Corbett, Michael T.,Goodman, C. Guy,Johnson, Jeffrey S.
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supporting information
p. 20197 - 20206
(2013/02/23)
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- 3- and 4-uloses derived from N-acetyl- D -glucosamine: A unique pair of complementary organocatalysts for asymmetric epoxidation of alkenes
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The 4-ulose and the 3-ulose, both derived in two steps from the α-methyl glycoside of N-acetyl-D-glucosamine (GlcNAc), act as organocatalysts in the asymmetric epoxidation of alkenes, with unprecedented complementary enantioselectivity. The best results are found with α,β-unsaturated esters as substrates, with enantiomeric ratios up to 90:10 and 11:89, respectively. Copyright
- Schoeberl, Christof,Jaeger, Volker
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supporting information; experimental part
p. 790 - 796
(2012/05/04)
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- Lewis acid-promoted electron transfer deoxygenation of epoxides, sulfoxides, and amine N-oxides: the role of low-valent niobium complexes from NbCl5 and Zn
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A mild and operationally simple deoxygenation of epoxides, sulfoxides, and amine N-oxides is described using a sub-stoichiometric amount of low-valent niobium complexes generated in situ from commercially available NbCl5 and zinc dust. The deoxygenation proceeds by a reductive cleavage of polarized O-C/O-N/O-S bonds through a single electron transfer from zinc metal to the niobium-substrate complex due to the high oxophilic nature of the niobium species. The presence of adjacent radical-stabilizing groups is beneficial to epoxide substrates; however the similar prerequisite does not apply to sulfoxides and amine N-oxides, where a broad range of substrates are efficiently deoxygenated in excellent yields.
- Oh, Kyungsoo,Knabe, William Eric
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supporting information; experimental part
p. 2966 - 2974
(2009/05/30)
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- Solid sodium hydroxide - THF, convenient system for synthesis esters of glycidic acids by darzens condensation
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Isopropyl- and tert-butylchloroacetate react with carbonyl compounds in the presence of powdered sodium hydroxide in THF, without a catalyst, giving substituted glycidates. The process is applied for preparation of glycidates from ketones, hitherto unavailable by phase-transfer catalyzed Darzens condensation.
- Gadaj,Kowalkowska,Jonczyk
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p. 577 - 584
(2008/09/19)
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- Darzens reaction promoted by KF/alumina: A novel stereoselective method for rapid and efficient synthesis of trans-α,β-epoxy ketones
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The Darzens condensation of α-chloroacetophenone with various aromatic aldehydes mediated by potassium fluoride on alumina at room temperature resulted in formation of good to excellent yields of trans-α,β-epoxy ketones in short time periods. Copyright Ta
- Sharifi, Ali,Salimi, Roghiyeh,Mirzaei, Mojtaba,Abaee, M. Saeed
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p. 1825 - 1832
(2008/02/02)
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- Arabinose-derived ketones as catalysts for asymmetric epoxidation of alkenes
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Readily available arabinose-derived ketones, containing a tunable butane-2,3-diacetal as the steric blocker, displayed increasing enantioselectivity (up to 90% ee) with the size of the acetal alkyl group in catalytic asymmetric epoxidation of trans-disubstituted and trisubstituted alkenes. The stereochemical communication between our ketone catalysts and the alkene substrates is mainly due to steric effect, and electronic effect involving π-π interaction between phenyl groups of substrate and of catalyst did not appear to be operative in our system.
- Shing, Tony K. M.,Leung, Gulice Y. C.,Luk, To
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p. 7279 - 7289
(2007/10/03)
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- Convenient synthesis of t-butyl Z-3-substituted glycidates under conditions of phase-transfer catalysis
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Reactions of mixtures of t-butyl E- and Z-3-substituted glycidates 1a-h with 50% aq. sodium hydroxide and a catalyst, benzyltriethylammonium chloride, TEBAC in dichloromethane (phase-transfer catalysis, PTC) led to preferential hydrolysis of the E-isomers to afford pure (90-98%) t-butyl Z-3-substituted glycidates 1a-i in good yields; PTC cleavage of glycidates additionally substituted at C-2, 1g or C-3, 1h,i suggests that an aryl group in the Z isomers hampers attack of HO- on the carbonyl carbon atom. As described in the literature, the diastereoselective PTC synthesis of Z-3-substituted glycidates and glycidonitriles consists of fast hydrolysis of E isomers present in mixtures with Z ones.
- Jonczyk, Andrzej,Zomerfeld, Tomasz
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p. 2359 - 2361
(2007/10/03)
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- Diastereoselective Darzens reactions of α-chloroesters, amides and nitriles with aromatic aldehydes under phase-transfer catalyzed conditions
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The development of the highly diastereoselective catalytic synthesis of glycidic acid derivatives via Darzens reaction is described. The reaction of α-chloroesters and amides with aromatic aldehydes smoothly proceeds in the presence of a quaternary ammonium salt as a phase-transfer catalyst to give the corresponding cis and trans desired products in satisfactory yields, respectively.
- Arai, Shigeru,Suzuki, Yukari,Tokumaru, Kazuyuki,Shioiri, Takayuki
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p. 833 - 836
(2007/10/03)
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- Improved procedure for Julia-Colonna asymmetric epoxidation of α,β-unsaturated ketones: Total synthesis of diltiazem and Taxol side-chain
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Poly-L-leucine catalyses the asymmetric epoxidation of enones 1-6 efficiently in a non-aqueous medium to provide the epoxy ketones 7-12 (70-91% yield; 80 to ≥95% ee). The strategy was used to make diltiazem 16 and the Taxol side chain 23 in single enantiomer form.
- Adger, Brian M.,Barkley, James V.,Bergeron, Sophie,Cappi, Michael W.,Flowerdew, Benjamin E.,Jackson, Mark P.,McCague, Ray,Nugent, Thomas C.,Roberts, Stanley M.
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p. 3501 - 3507
(2007/10/03)
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- Process for the preparation of (2R,3R)-cis)-β-phenylglycidic acid
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A method for preparing β-phenylglycidic-(2R, 3R) acid optionally in the form of salt or ester by precipitation of the salt of the β-phenylglycidic-(2R,3R) acid with (+)-α-methylbenzylamine-(R) in a solution of a mixture of salts of cis and trans β-phenylglycidic acids with (+)-α-methylbenzylamine(R)- and the use of the resulting product for preparing taxol and its analogs.
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- A Novel Darzens-Type Reaction Promoted by Tributylstannylcarbamate
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Stannylcarbamate 1 proved to be a selective agent for generating organotin(IV) enolates from α-halo ketones.Thus, a Darzens reaction was achieved under mild and neutral conditions.The reaction took place without any side reactions and even with aliphatic α-halo ketones bearing enolizable α'-hydrogens.Various types of α,β-epoxy ketones and esters were obtained in this one-pot reaction.The stereoselectivity of the reaction was influenced by changing the halogen substituent of the α-halo ketones and by additives.Moreover, the present method could be appliedto γ- and δ-halo ketones as enolate precursors, and five- and six-membered cyclic compounds were obtained.
- Shibata, Ikuya,Yamasaki, Hayahide,Baba, Akio,Matsuda, Haruo
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p. 6909 - 6914
(2007/10/02)
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- Highly enantioselective routes to Darzens and acetate aldol products from achiral aldehydes and t-butyl bromoacetate
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New methodology is described for the enantioselective coupling of t-butyl bromoacetate with aldehydes to give anti-α-bromo β-hydroxy esters (1), useful precursors of chiral glycidic esters (2), acetate aldols (3), β-amino acid esters (4) and α-amino acid
- Corey,Choi
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p. 2857 - 2860
(2007/10/02)
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- A stereocontrolled approach to electrophilic epoxides
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Lithium t-butyl hydroperoxide (easily generated by addition of an alkyl-lithium to anhydrous t-butyl hydroperoxide in THF solution) is a powerful reagent for the epoxidation of electrophilic alkenes at -20 to 0 °C under full stereocontrol. Thus αβ-unsaturated esters, sulphones, sulphoximines, and amides are readily epoxidised with complete regio- and stereo-specificity and with considerable chiroselectivity (20-100%) when appropriate chiral auxiliaries such as menthyl, 8-phenylmenthyl, or a camphor-sulphonamide derivative are used. Asymmetric αβ-unsaturated sulphoximines undergo epoxidation with 100% diastereoselectivity. The only exceptions to stereocontrol noted are heavily substituted maleate esters such as di-t-butyl maleate. The αβ-epoxy amides are shown to be valuable sources of the corresponding epoxy ketones by treatment with an organolithium, allowing a stereo- and chemoselective entry in high yield to these useful intermediates.
- Meth-Cohn, Otto,Moore, Clive,Taljaard, Heinrich C.
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p. 2663 - 2674
(2007/10/02)
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