- Highly regio- and stereoselective reductions of carbonyl compounds in aqueous glycosidic media
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Highly regioselective reductions of α,β-unsaturated ketones to the corresponding allylic alcohols were performed in essentially quantitative yields in aqueous media containing either glycosidic surfactants or amphiphilic carbohydrates. Reductions of cyclohexanones and cyclohexenones lead under the same conditions, stereoselectively to reduced compounds bearing an equatorial alcohol function. Hydrophobic interactions between amphiphilic carbohydrates and lipophilic substrates were modelized and should account for the observed stereodifferentiation.
- Denis, Cecile,Laignel, Benoit,Plusquellec, Daniel,Le Marouille, Jean-Yves,Botrel, Alain
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- Enantioselective syntheses and fragrance properties of the four stereoisomers of Magnolione (magnolia ketone)
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Enantioselective total syntheses of the four stereoisomers of the fragrance Magnolione (1) are described. Key step is a Pd-catalyzed asymmetric allylic alkylation displaying enantiomer excess of ≥ 99% (Scheme 2). The resultant methyl α-acetyl-2-pentylcyclopent-2-ene-1-acetate) was subjected to demethoxycarbonylation, carbonyl protection by acetalization, and epoxidation (Schemes 2 and 3). Subsequent Lewis acid catalyzed epoxide/ketone rearrangement followed by deprotection gave cis/trans mixtures of Magnolione in 28% overall yield (Scheme 3). The cis/trans isomers were separated by prep. HPLC, and fragrance properties as well as odor threshold values were determined (Table 2).
- Stang, Andrea Quendolin,Helmchen, Guenter
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- HYDROGENATION OF ALDEHYDE OR KETONE COMPOUNDS WITH FE/TRIDENTATE LIGANDS COMPLEXES
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The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of Fe complexes with tridentate ligands, having one amino or imino coordinating group and two phosphino coordinating groups, in hydrogenation processes for the reduction of ketones or aldehydes, into the corresponding alcohol or diol, respectively.
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Page/Page column 25-27
(2017/01/02)
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- HYDROGENATION OF ESTERS OR CARBONYL GROUPS WITH TETRADENTATE AMINO/IMINO-THIOETHER BASED RUTHENIUM COMPLEXES
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The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of specific ruthenium catalysts, or pre-catalysts, in hydrogenation processes for the reduction of ketones and/or aldehydes into the corresponding alcohol respectively. Said catalysts are ruthenium complexes comprising a tetradentate ligand (L4) coordinating the ruthenium with: two nitrogen atoms, each in the form of a primary or secondary amine (i.e. a NH2 or NH group) or N-alkyl imine functional groups (i.e. a C═N group), and two sulfur atoms, each in the form of thioether functional groups.
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Paragraph 0113; 0114
(2013/10/22)
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- Enantioselective reduction of ketones with a silane agent/metal compound/chiral ligand system
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A process for the enantioselective reduction of prochiral ketones to chiral alcohols by (a) the reaction of a prochiral ketone with a silane agent, which is present in a stoichiometric quantity, in the presence of a catalyst derived from a Zn, Co or Cd precursor compound and from a chiral amine, imine, alcohol or amino alcohol ligand; (b) the hydrolysis of the siloxane obtained using an appropriate agent; and (c) the separation and purification of the optically active alcohol formed. Polymethylhydrosiloxane (PMHS) is a preferred silane agent, zinc is a preferred metal, and the precursor compound is produced by reacting a salt or complex of the respective metal with the reducing agent. In another embodiment, an appropriate salt of the chosen metal is used directly in the reaction with the chiral ligand to produce the catalytic form after reaction with the ligand. The process enables high enantiomeric excesses (ee) to be obtained in chiral alcohols.
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Page column 18-20
(2008/06/13)
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- A new variant of the Claisen rearrangement from malonate-derived allylic trimethylsilyl ketene acetals: Efficient, highly enantio- and diastereoselective syntheses of (+)-methyl dihydroepijasmonate and (+)-methyl epijasmonate
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Complete chirality transfer occurs in the smooth Claisen rearrangement of the trimethylsilyl (TMS) ketene acetals, which were prepared from allylic malonates (R)-1 (R = pentyl, 2-(Z)-pentenyl). These are in turn accessible by enantioselective reduction/esterification or by enzymatic kinetic resolution. The cis configuration in (+)-3 was achieved by highly syn-selective epoxidation of (+)-2, followed by suprafacial 1,2-H migration.
- Fehr, Charles,Galindo, Jose
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p. 569 - 573
(2007/10/03)
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- A Simple and Efficient Synthesis of (+/-)-Methyl Dihydroepijasmonate
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An efficient synthesis of the less stable cis-isomer, methyl dihydroepijasmonate 8, is described.
- Kitahara, Takeshi,Hamaguchi, Katsuhiko,Warita, Yasuhiro,Takagi, Yoshikazu,Mori, Kenji
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p. 1867 - 1872
(2007/10/02)
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