- Hypervalent Iodine(III)-Catalysed Enantioselective α-Acetoxylation of Ketones
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An enantioselective catalytic synthesis of α-acetoxylated ketones through I(I)/I(III) catalysis using a resorcinol/lactamide-based chiral iodoarene is reported. Catalyst turnover by in situ generation of the active iodine(III) derivative is achieved by oxidation with mCPBA in the presence of acetic acid. The prior transformation of ketones to easily accessible acetyl enol ethers is beneficial and yields up to 97 percent with enantioselectivities up to 88 percent ee are obtained using only low catalyst loadings of only 5 mol percent under mild reaction conditions.
- Hokamp, Tobias,Wirth, Thomas
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supporting information
p. 10417 - 10421
(2020/07/24)
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- Asymmetric Oxidation of Enol Derivatives to α-Alkoxy Carbonyls Using Iminium Salt Catalysts: A Synthetic and Computational Study
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We report herein the first examples of asymmetric oxidation of enol ether and ester substrates using iminium salt organocatalysis, affording moderate to excellent enantioselectivities of up to 98% ee for tetralone-derived substrates in the α-hydroxyketone products. A comprehensive density functional theory study was undertaken to interpret the competing diastereoisomeric transition states in this example in order to identify the origins of enantioselectivity. The calculations, performed at the B3LYP/6-31G(D) level of theory, gave good agreement with the experimental results, in terms of the magnitude of the effects under the specified reaction conditions, and in terms of the preferential formation of the (R)-enantiomer. Just one of the 30 characterized transition states dominates the enantioselectivity, which is attributed to the adoption of an orientation relative to stereochemical features of the chiral controlling element that combines a CH interaction between a CH2 group in the substrate and one of the aromatic rings of the biaryl section of the chiral auxiliary with a good alignment of the acetoxy group with the other biaryl ring, and places the smallest substituent on the alkene (a hydrogen atom) in the most sterically hindered position.
- Page, Philip C. Bulman,Almutairi, Saud M.,Chan, Yohan,Stephenson, G. Richard,Gama, Yannick,Goodyear, Ross L.,Douteau, Alice,Allin, Steven M.,Jones, Garth A.
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p. 544 - 559
(2019/01/11)
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- Palladium-Catalyzed Oxidative Synthesis of α-Acetoxylated Enones from Alkynes
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We report a palladium-catalyzed oxidative functionalization of alkynes to generate α-acetoxylated enones in one step. A range of functional groups are well-tolerated in this reaction. Mechanistic studies, including the use of 18O-labeled DMSO,
- Jiang, Tuo,Quan, Xu,Zhu, Can,Andersson, Pher G.,B?ckvall, Jan-E.
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supporting information
p. 5824 - 5828
(2016/05/09)
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- A simple synthetic route to enantiopure α-hydroxy ketone derivatives by asymmetric hydrogenation
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High enantioselectivities (up to 99% ee) have been observed for the catalytic asymmetric hydrogenation of the α-ketone enol acetates. DuanPhos has been proved to be the most effective ligand for this reaction. The high yield and enantioselectivity of the asymmetric hydrogenation of the α-ketone enol acetates represents a feasible synthetic route to important pharmaceutical building blocks: α-hydroxy ketones. Copyright
- Sun, Tian,Zhang, Xumu
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p. 3211 - 3215
(2013/01/15)
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- NMR determination of absolute configuration of α-acyloxy ketones
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Determination of the absolute configuration of several acyclic α-acyloxy-ketones, and δ-ketobutanolides, in the presence of a chiral solvating agent, by low temperature and low concentration 1H NMR analysis, is reported.
- Jullian, Jean-Christophe,Franck, Xavier,Latypov, Shamil,Hocquemiller, Reynald,Figadere, Bruno
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p. 963 - 966
(2007/10/03)
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- Simple chemoenzymatic access to enantiopure pharmacologically interesting (R)-2-hydroxypropiophenones
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A chemoenzymatic synthesis of pharmacological interesting (R)-2-hydroxypropiophenones starting from propiophenone derivatives is described. Manganese(III) acetate-mediated acetoxylation followed by fungus-mediated hydrolysis of propiophenone derivatives affords (R)-2-hydroxypropiophenones in high enantiomeric excess.
- Demir, Ayhan S.,Hamamci, Haluk,Sesenoglu, Ozge,Aydogan, Feray,Capanoglu, Doga,Neslihanoglu, Rahsan
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p. 1953 - 1956
(2007/10/03)
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- Enantioselective synthesis and stereoselective rearrangements of enol ester epoxides
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Enol esters can be epoxidized with high enantioselectivities using the fructose-derived chiral ketone 1 as catalyst and Oxone as oxidant. A detailed study of enantiomerically enriched enol ester epoxides has revealed that the acid-catalyzed rearrangement can proceed through two distinct pathways, one with retention of configuration and the other with inversion. The competition between the two pathways is highly dependent upon the nature of the acid catalyst. A strong acid favors retention of configuration and a weak acid favors inversion of configuration. Under thermal conditions, these epoxides rearrange highly stereoselectively with inversion of configuration. Either enantiomer of an α-acyloxy ketone can be formed from one enantiomer of an enol ester epoxide by judicious choice of reaction conditions.
- Zhu,Shu,Tu,Shi
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p. 1818 - 1826
(2007/10/03)
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- A simple procedure for the synthesis of enantiopure α-acetoxy ketones
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Cross-coupling reactions of α-acetoxy carboxylic acid chlorides with organocopper reagents, derived from Grignard reagents, cuprous bromide and lithium bromide, provide a simple and straightforward method for the synthesis of enantiopure α-acetoxy ketones.
- Babudri, Francesco,Fiandanese, Vito,Marchese, Giuseppe,Punzi, Angela
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p. 2431 - 2440
(2007/10/03)
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- Highly enantioselective epoxidation of enol silyl ethers and esters
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High enantioselectivities have been obtained for asymmetric epoxidation of enol silyl ethers and esters using a fructose-derived chiral ketone as catalyst and Oxone as oxidant.
- Zhu, Yuanming,Tu, Yong,Yu, Hongwu,Shi, Yian
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p. 7819 - 7822
(2007/10/03)
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- Synthesis and Rhizopus oryzae mediated enantioselective hydrolysis of α-acetoxy aryl alkyl ketones
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Mn(OAc)3 oxidation of aromatic ketones afforded the α-acetoxy ketones in good yield. Selective hydrolysis of the acetoxy ketones by the fungus Rhizopus oryzae yields (R)-hydroxy ketones in high enantiomeric excess.
- Demir, Ayhan S.,Hamamci, Haluk,Tanyeli, Cihangir,Akhmedov, Idris M.,Doganel, Fatos
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p. 1673 - 1677
(2007/10/03)
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- Enantioselective Preparation of α-Acyloxy Ketones from α-Hydroxy and α-Amino Acids
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Various chiral α-acyloxy ketones have been easily prepared, in high yields with an excellent enantiomeric purity, by acylation of organomanganese reagents with the corresponding α-acyloxy carboxylic acid chlorides prepared from α-hydroxy and α-amino acids.
- Cahiez, Gerard,Metais, Eric
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p. 6449 - 6452
(2007/10/02)
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- Resolution of Secondary α-Ketoalcohols Catalyzed by Lipase and Inversioon of Stereochemistry
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Several α-ketoalcohols of synthetic value were resolved using lipase as a catalyst.Lipoprotein lipase (LPL) provided the best rate of hydrolysis and kinetic differentiation.One of these optically pure α-ketoalcohol was converted to (S)-ibuprofen in good optical purity.The stereospecific inversion of (R)-alcohol to (S)-alcohol is described.Key Words Enzymatic resolution; α-Ketoalcohol; (S)-Ibuprofen
- Duh, Tsai-Hui,Wang, Yi-Fong,Wu, Ming-Jung
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p. 579 - 584
(2007/10/02)
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- Enzymes in Organic Synthesis: Lipase Catalyzed Resolution of Secondary α-Ketoalcohols
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Resolution of several α-ketoalcohols of synthetic value using lipase as a catalyst is described.
- Duh, Tsai-Hui,Wang, Yi-Fong,Wu, Ming-Jung
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p. 1793 - 1794
(2007/10/02)
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- Fluoride Ion Catalyzed Reduction of Aldehydes and Ketones with Hydrosilanes. Synthetic and Mechanistic Aspects and an Application to the Threo-Directed Reduction of α-Substituted Alkanones
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Reduction of aldehydes and ketones with hydrosilanes proceeded in the presence of a catalytic amount of tetrabutylammonium fluoride or tris(diethylamino)sulfonium difluorotrimethylsilicate in aprotic polar solvents under mild conditions.A significant isotope effect (kH/kD = 1.50) was observed in competitive reduction of acetophenone with HSiMe2Ph and DSiMe2Ph.The reaction was of first order in the concentration of an aprotic polar solvent HMPA.Reduction of 2-methylcyclohexanone gave cis-2-methylcyclohexanol with selectivities up to 95percent.The kinetic and stereochemical results suggest that a hexavalent fluorosilicate - is involved. α-Alkoxy (acyloxy or dimethylamino) ketones were transformed to threo alcohols in high diastereoselectivities.The reduction was also applied to α-methyl-β-keto amides, RCOCH(MeCONR)2, to afford the corresponding threo alcohols in >98percent selectivity.The threo selectivity is explained in terms of the Felkin-Anh model in which interaction of carbonyl oxygen with a countercation is ideally suppressed.The threo-directed reduction was applied to (R)-1-phenyl-4-(2-tetrahydropyranyloxy)-1-penten-3-one and N-(2-benzoylpropanoyl)piperidine.The resulting threo alcohols were respectively converted into (2R,3S)-2,3-(cyclohexylidenedioxy)butanal, a key intermediate of daunosamine synthesis, and into a pharmacologically useful compound threo-N-(3-hydroxy-2-methyl-3-phenylpropyl)piperidine.
- Fujita, Makoto,Hiyama, Tamejiro
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p. 5405 - 5415
(2007/10/02)
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