- Asymmetric dihydroxylation of olefins containing sulfur: Chemoselective oxidation of C-C double bonds in the presence of sulfides, 1,3-dithianes, and disulfides
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Osmium tetroxide catalyzed oxidation of sulfide containing olefins in the presence of the chiral ligands (DHQD)2PHAL and (DHQ)2PHAL resulted in the chemoselective oxidation of the C-C double bond rather than oxidation at sulfur. The
- Walsh,Pui Tong Ho,King,Sharpless
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- Synthesis of an advanced intermediate enroute to thiomarinol antibiotics
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A stereoselective synthesis of the C1-C14 fragment of thiomarinols is disclosed. The key steps include the stereoselective preparation of an allylic sulfide via a chloro sulfide by 1,2-asymmetric induction, ring-closing metathesis reaction, Kirmse-Doyle reaction for the preparation of a γ,δ-unsaturated ester, Nozaki-Hiyama-Kishi coupling and Julia-Kocienski olefination reaction. Substrate controlled asymmetric induction has been advantageously employed for the creation of stereogenic centers. Noyori transfer hydrogenation and asymmetric hydrogenation reactions have been utilized for the creation of carbinol stereocenters.
- Raghavan, Sadagopan,Ravi, Anil
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p. 2814 - 2823
(2017/04/14)
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- OsO4?streptavidin: A tunable hybrid catalyst for the enantioselective cis-dihydroxylation of olefins
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Taking control: Selective catalysts for olefin dihydroxylation have been generated by the combination of apo-streptavidin and OsO4. Site-directed mutagenesis allows improvement of enantioselectivity and even inversion of enantiopreference in certain cases. Notably allyl phenyl sulfide and cis-β-methylstyrene were converted with unprecedented enantiomeric excess.
- Koehler, Valentin,Mao, Jincheng,Heinisch, Tillmann,Pordea, Anca,Sardo, Alessia,Wilson, Yvonne M.,Knoerr, Livia,Creus, Marc,Prost, Jean-Christophe,Schirmer, Tilman,Ward, Thomas R.
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supporting information; experimental part
p. 10863 - 10866
(2012/02/01)
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- Bacillus alcalophilus MTCC10234 catalyzed enantioselective kinetic resolution of aryl glycidyl ethers
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The phenyl glycidyl ether derivatives have been kinetically resolved with the growing cells of Bacillus alcalophilus MTCC10234 yielding (S)-epoxides with up to >99% ee and (R)-diols with up to 89% ee. The enantiomeric ratio (E) of up to 67 has been obtained for biohydrolysis process. The effect of different substituents of phenyl glycidyl ether on the biocatalytic efficiency of B. alcalophilus MTCC10234 showed preference for methyl- and chloro-substituted aryl glycidyl ether derivatives whereas nitro-derivatives were transformed at a slower rate. 2,6-Dimethylphenyl glycidyl ether which contains a bulky aryl group having methyl group on both the ortho positions was resolved with an E=39.
- Bala, Neeraj,Chimni, Swapandeep Singh,Saini, Harvinder Singh,Chadha, Bhupinder Singh
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experimental part
p. 128 - 134
(2010/10/04)
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- Osmium-Catalyzed Dihydroxylation of Olefins Using Dioxygen or Air as the Terminal Oxidant
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The osmium-catalyzed dihydroxylation of various olefins using molecular oxygen or air as the stoichiometric oxidant is reported. Aromatic olefins yield the corresponding diols in good to excellent chemoselectivities under optimized pH conditions (pH = 10.4-12.0). Air can be used under moderate pressures (3-9 bar) instead of dioxygen as the reoxidant. By increasing the oxygen content of the solution, it is possible to achieve highly efficient conversion at low catalyst amount (catalyst/substrate = 1:4000). Tri- and tetrasubstituted olefins are oxidized at pH > 11 to give the corresponding 1,2-diols in good to very good yields without requiring the addition of sulfonamides or other hydrolysis agents. Studies of the dihydroxylation of functionalized olefins demonstrate that the reaction conditions tolerate a variety of functional groups. In the presence of dihydroquinine or dihydroquinidine derivatives (Sharpless ligands), asymmetric dihydroxylations occur with lower enantioselectivities than tose of the classical K3[Fe(CN)6] reoxidation system.
- Doebler, Christian,Mehltretter, Gerald M.,Sundermeier, Uta,Beller, Matthias
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p. 10289 - 10289
(2007/10/03)
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- Novel synthesis and enzymatic resolution of (±)-2,3-epoxy propyl esters
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A novel method of synthesizing glycidyl esters (±) -2,3-epoxy propyl esters has been developed involving reaction of epichlorohydrin with sodium salt of carboxylic acids in the presence of 15-crown-5 as catalyst with excellent yields. Enzymatic resolution of these glycidyl esters by lipasePS- C has been achieved with remarkable substrate selectivity.
- Nair, Ranjeet V.,Patil, Prashant N.,Salunkhe, Manikrao M.
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p. 2559 - 2566
(2007/10/03)
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- The efficient resolution of protected diols and hydroxy aldehydes by lipases: Steric auxilliary approach and synthetic applications
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1,n-Diols (n = 2-5) and 2-hydroxy aldehydes protected with a steric auxilliary are transformed by Pseudomonas lipases with high enantioselectivity, thus allowing the efficient resolution of these molecules and the synthesis of related derivatives with high optical purity.
- Kim,Lim,Choi,Whang,Ku,Choi
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- Catalytic asymmetric epoxidation
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Improved method for epoxidation of ethylenic alcohols is provided employing catalytic amounts of a titanium-glycol catalyst and a peroxide under mild conditions which provide for the continuous maintenance of an anhydrous medium during catalyst formation and during the course of the reaction. Conveniently, molecular sieves may be employed.
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- Optical Resolution and Chiral Synthesis of Methyl 6,7-Dichloro-2,3-dihydrobenzofuran-2-carboxylate
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Optical isomers of methyl 6,7-dichloro-2,3-dibenzofuran-2-carboxylate (2) were prepared by means of both optical resolution and chiral synthesis.The resolution of the carboxylic acid 3 was achieved in a practical and efficient way via the l- and d-menthyl esters, which were directly converted to enantiomers of 2.Chiral synthesis of 2 was attained with high optical yield via acid-catalyzed cyclization of the β-hydroxysulfide 10 derived from optically active glycidyl phenyl sulfide 13.The optical resolution method was considered to be better for large-scale preparation from the economical and operational viewpoints.Keywords - methyl 6,7-dichloro-2,3-dibenzofuran-2-carboxylate; optical resolution; (R)-4-phenyl-2-oxazolidone; menthol; chiral synthesis; glycidyl phenyl sulfide; β-hydroxysulfide; episulfonium ion; S-8666
- Yodo, Mitsuaki,Matsushita, Yoshihiro,Ohsugi, Eiichi,Harada, Hiroshi
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p. 902 - 913
(2007/10/02)
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- OPTICALLY PURE (S)-3-PHENYLTHIO-1,2-PROPANEDIOL: SYNTHESIS BY THE YEAST REDUCTION AND USE AS A PRECURSOR OF BOTH ENANTIOMERS OF SECONDARY ALCOHOLS
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Optically pure (S)-3-phenylthio-1,2-propanediol was obtained by the enantioselective reduction of 1-hydroxy-3-phenylthio-2-propanone with the Baker's yeast, and was found to be a convenient precursor for both enantiomers of secondary alcohols, which was d
- Fujisawa, Tamotsu,Itoh, Toshiyuki,Nakai, Mikio,Sato, Toshio
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p. 771 - 774
(2007/10/02)
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