- Borane-Catalyzed Direct Asymmetric Vinylogous Mannich Reactions of Acyclic α,β-Unsaturated Ketones
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Herein, we report that, by using chiral bicyclic bisborane catalysts, we have achieved the first highly regio-, diastereo-, and enantioselective direct asymmetric vinylogous Mannich reactions of acyclic α,β-unsaturated ketones. The strong Lewis acidity and steric bulk of the bisborane catalysts were essential for the observed high yields and selectivities.
- Tian, Jun-Jie,Liu, Ning,Liu, Qi-Fei,Sun, Wei,Wang, Xiao-Chen
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p. 3054 - 3059
(2021/03/01)
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- Highly enantioselective synthesis of optically active ketones by iridium-catalyzed asymmetric hydrogenation
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(Chemical Equation Presented) Close to perfect enantioselectivity (up to 99% ee, see scheme) is found for the formation of α-substituted ketones by the asymmetric hydrogenation of enones with an iridium-phosphinooxazoline catalyst. In an operationally simple process, both linear and cyclic substrates react well and afford the desired products in high yields. A wide variety of substituents are tolerated, thus making the method synthetically appealing.
- Lu, Sheng-Mei,Bolm, Carsten
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supporting information; experimental part
p. 8920 - 8923
(2009/05/30)
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- Neodymium(III)-mediated reformatsky-type reactions of α-halo ketones with carbonyl compounds
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In a neodymium(III) iodide induced process, α-bromo ketones 1 and aldehydes 2 are effectively converted into aldol products 3. This Reformatsky-type reaction proceeds through the formation of a neodymium enolate at room temperature in CH2Cl2. The analogous reaction in the presence of NdBr3/NaI at 50°C in THF favors the formation of corresponding aldol-Tishchenko products 5 in good yields. Studies to define the scope and limitations of these reactions mediated by neodymium(III) salts are also described. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Kirsch, Stefan F.,Liebert, Clemence
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p. 3711 - 3717
(2008/03/18)
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- Increased lewis acidity in hafnium-substituted polyoxotungstates
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Monolacunary polyoxotungs-tates [α1-P2W 17O61]10 and [α-PW11O 39]10 react with HfGl4 to yield [α1-HfP2W17O61]su
- Boglio, Cecile,Micoine, Kevin,Remy, Pauline,Hasenknopf, Bernold,Thorimbert, Serge,Lacote, Emmanuel,Malacria, Max,Afonso, Carlos,Tabet, Jean-Claude
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p. 5426 - 5432
(2008/02/09)
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- Diastereomer-differentiating photochemistry of β-arylbutyrophenones: Yang cyclization versus type II elimination
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The diastereomers of ketones 2 and 3 are shown to exhibit distinct photochemical reactivities due to conformational preferences; while the anti isomers of 2 and 3 undergo efficient Yang cyclization in 75-90% yields with a remarkable diastereoselectivity (> 90%), the syn isomers predominantly undergo Norrish Type II elimination. The differences in the product profiles of the diastereomers are consistent with a mechanistic picture involving the formation of precursor diastereomeric triplet 1,4-biradicals in which the substituents at α and β-positions stabilize the cisoid (cyclization) or transoid (elimination) geometry. The fact that such a diastereomeric relationship does indeed ensue at the triplet-excited-state itself is demonstrated via the nanosecond laser-flash photolysis of model ketones 1. The diastereomeric discrimination in the product profiles observed for ketones 2 and 3 as well as in the triplet lifetimes observed for ketones 1 can both be mechanistically traced back to different conformational preferences of the ground-state diastereomeric ketones and the intermediary 1,4-biradicals. Additionally, it emerges from the present study that the syn and anti diastereomers of ketones 2 and 3 represent two extremes of a broad range of widely examined butyrophenones, which lead to varying degrees of Yang photocyclization depending on the alkyl substitution pattern.
- Singhal, Nidhi,Koner, Apurba L.,Mal, Prasenjit,Venugopalan, Paloth,Nau, Werner M.,Moorthy, Jarugu Narasimha
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p. 14375 - 14382
(2007/10/03)
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- Stereocontrol in one-pot syntheses of 1,3-diols
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Titanium mediated aldol addition reduction sequence is described for the synthesis of stereodefined 1,3-diols. Diastereochemical control is surprisingly achieved through the careful selection of starting materials used.
- Mahrwald,Ziemer
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p. 14005 - 14012
(2007/10/03)
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- Reformatsky Type Reaction Promoted by Hexabutyldistannane
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Bu3SnSnBu3 proved to be effective reagent for Reformatsky type reaction.The use of Bu2SnI2 as an additive was essential, which proved to be effective for generation of organotin (IV) enolates.From the reaction with aldehydes, aldol type products were obta
- Shibata, Ikuya,Yamaguchi, Takashi,Baba, Akio,Matsuda, Haruo
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- ERYTHRO SELECTIVE ALDOL CONDENSATION USING TITANIUM ENOLATES
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Titanium enolates derived from ketones and esters react with aldehydes to afford erythro adducts with high diastereoselection.
- Reetz, M. T.,Peter, R.
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p. 4691 - 4694
(2007/10/02)
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