- Enantioselective hydrogenation of β-keto esters catalyzed by P-chiral bis(dialkylphosphino)ethanes-Ru(II)
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Asymmetric hydrogenation of keto esters using a BisP*-RuBr2 catalyst is reported. High enantioselectivities up to 98% were achieved in the hydrogenation of β-keto esters.
- Yamano, Toru,Taya, Naohiro,Kawada, Mitsuru,Huang, Taisheng,Imamoto, Tsuneo
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p. 2577 - 2580
(2007/10/03)
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- Stereo- and chemoselective transfer hydrogenation of carbonyl groups with RuCl2(PPh3)3 and BINAP-Ru as catalysts and et3NH+H2PO2-·1,5H 2O as a hydrogen donor
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Using Et3NH+H2PO2-.1.5 H2O as a hydrogen donor, the RuCl2(Ph3P)3, RuCl2(PPh3)3 / C and BINAP-Ru proved highly active catalysts for transfer hydrogenation of ketones under milder conditions than other hydrogen donors. 2-Methyl-, 2-chloro-, 2-(ethoxycarbonyl)cyclohexanones and -cyclopentanones were reduced to the less stable axial alcohols in excellent diastereoisomeric excess (de: 90-100%), and the carbonyl group of α,β-unsaturated ketones was selectively reduced, in contrast with other hydrogen donors the C=C bond was reduced. Copyright
- Khai, Bui The,Arcelli, Antonio
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p. 6599 - 6602
(2007/10/03)
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- 65. Homogeneous and Heterogeneous Asymmetric Reactions. Part 5. Diastereoselective and Enantioselective Hydrogenation of Cyclic β-Keto Esters on Modified Raney-Nickel Catalysts
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The hydrogenations of methyl 2-oxocyclopentanecarboxylate (1), ethyl 2-oxocyclohexanecarboxylate (3), and 2-methylcyclohexanone (5) on unmodified Raney-Ni catalyst lead predominantly to the formation of the cis-hydroxy diastereoisomers of 2, 4, and 6, respectively (Scheme 2).In the asymmetric hydrogenations on catalysts modified with chiral tartaric acid (R,R)-C4H6O6/Raney-Ni and (R,R)-C4H6O6/NaBr/Raney-Ni), the predominance of the cis-isomer increases significantly.The hydrogenations of β-keto esters 1 and 3 proceed with an enantioselectivity of 10-15percent on the modified catalysts, while the similar hydrogenation of 5 yields optically inactive 6.The (1S,2R)-enantiomers of the cis-isomers of 2 and 4 are formed in larger quantity, whereas the (1R,2R)-enantiomers of the corresponding trans-isomers predominate (Scheme 1).The enantioselective formation of trans-2 and trans-4 can be interpreted mainly in terms of the asymmetric hydrogenation of cyclic β-keto esters through the keto form, while that of the corresponding cis-hydroxy esters proceeds through the enol form.
- Wittmann, Gyula,Goendoes, Gyoergy,Bartok, Mihaly
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p. 635 - 639
(2007/10/02)
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