Enantioselecttve hydrogenation of isophorone

Tungler, Antal; Máthé, T.; Petró, J.; Tarnai, Tibor

doi:10.1016/0304-5102(90)80001-y

Cited by 58 publications

(35 citation statements)

References 9 publications

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“…10 Reactions were run until a yield of at least 60% was obtained (as monitored by hydrogen gas consumption during reaction and subsequently by chiral gas chromatography). In every case, increasing the ligand concentration decreased the reaction rate and this retardation effect was most pronounced with the largest ligands.…”

Section: Resultsmentioning

confidence: 99%

Heterogeneously Catalyzed Asymmetric Hydrogenation of C═C Bonds Directed by Surface-Tethered Chiral Modifiers

et al. 2009

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. observed enantiomeric excesses increased with increasing size of the alkyl group in the sulfide. This likely reflects varying degrees of ligand dispersion on the surface: bulky substituent groups hinder close approach of ligand molecules to each other, inhibiting close-packed island formation, favoring dispersion as separate molecules and leading to effective asymmetric induction. Conversely, small substituents favor island formation leading to very low asymmetric induction. Enantioselective reaction most likely involves initial formation of an enamine or iminium species, confirmed by use of an analogous tertiary amine, which leads to racemic product. Ligand rigidity and resistance to selfassembled monolayer formation are important attributes that should be designed into improved chiral modifiers.

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Section: Resultsmentioning

confidence: 99%

Heterogeneously Catalyzed Asymmetric Hydrogenation of C═C Bonds Directed by Surface-Tethered Chiral Modifiers

et al. 2009

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“…Our studies on the subject indicated the strong connection between (i) and (iii). The original mechanistic model by Tungler et al strongly emphasized the importance of unsaturated ketone-proline complex formation prior to hydrogenation [11,12]. We have refined this model and have pointed that strong proline adsorption is necessary to obtain high enantioselectivities [13].…”

Section: Introductionmentioning

confidence: 87%

Nature of Proline-induced Enantiodifferentiation in Asymmetric Pd Catalyzed Hydrogenations: Is the Catalyst Really Indifferent?

et al. 2008

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The mode of enantioselection in the proline modified asymmetric hydrogenation of isophorone (3,5,5-trimethyl-2-cyclohexenone) on supported Pd catalysts has been studied. It is shown that several experimental factors, such as modifier structure and chemical nature of the catalyst support, strongly affect the outcome of the hydrogenations. Secondary kinetic resolution was found to be the major reason for obtaining high enantioselectivities on most catalysts. Extensive studies have been carried out to clarify the importance of the interaction of the prolinedihydroisophorone complex with the catalyst. The secondary kinetic resolution of dihydroisophorone was investigated under different conditions. First, racemicdihydroisophorone was studied using several (S)-proline modified supported Pd catalysts, then the individual enantiomers were subjected to a similar reaction on Pd/ BaCO 3 catalyst in the presence of (S)-proline. Our results provide convincing support for the heterogeneous enantioselection model under the current experimental conditions.

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“…Thus, the hydrogenation of acetophenone or isophorone on a Pd/C catalyst in the presence of a stoichiometric amount of (S)-proline resulted in 1-phenylethanol or dihydroisophorone with e.e.-values up to 80% [145][146][147][148][149].…”

Section: Diastereoselective Catalysis 3659mentioning

confidence: 99%

Diastereoselective Catalysis

Бессон

Pinel

2008

Handbook of Heterogeneous Catalysis

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IntroductionA reaction is referred to as stereoselective when a substrate S, which may yield a series of stereoisomer products (P 1 , P 2 , . . . P n ) gives preferentially -or even exclusively -one of these. Today, the preparation of stereoisomeric compounds is generating tremendous academic and industrial interest. Especially, the synthesis of enantiopure chiral compounds is becoming increasingly important in the production of pharmaceuticals, agrochemicals, fragrances, and flavor substances. Among the different methods used to prepare pure enantiomers, asymmetric catalysis plays an important role, particularly hydrogenation. Currently, two types of asymmetric hydrogenation with solid catalysts are utilized, namely enantioselective and diastereoselective synthesis.In enantioselective hydrogenation, one enantiomer of a chiral product is formed preferentially from a prochiral precursor, the stereoselectivity being induced by a chiral catalyst. Immobilization of very selective metal-ligand complexes and modification of active metals by an adsorbed chiral organic molecule (chiral modifier) have been extensively studied [1]. In some cases, high enantioselectivities approaching 98% enantiomeric excess (e.e.) have been obtained with modified supported metal catalysts. The numerous investigations devoted to the understanding of the mechanism have been summarized in several reviews [1][2][3][4][5]. The most effective catalysts are Ni-tartaric acid, Pt-cinchona, Pd-cinchona and, to a lesser extent, Rh-cinchona systems. The field of reaction types is still limited to a narrow range of asymmetric hydrogenations.The other frequently used catalytic strategy for the synthesis of pure enantiomers is based on diastereoselective hydrogenation. This involves the selective formation of one diastereoisomer by creating a new stereogenic center in a chiral molecule. In this approach, the reaction consists of three simple steps. First, a covalent bond between the prochiral substrate and a chiral moiety (chiral auxiliary) is formed. Then, the diastereoselective hydrogenation is performed over various noble metal catalysts, leading stereoselectively to a new chiral center. This step does not require a chiral catalyst, but the stereogenic center in the chiral auxiliary is able to induce the stereoselectivity. The desired molecule can finally be obtained by selective cleavage of the chiral auxiliary from the product which can be recycled.

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Enantioselecttve hydrogenation of isophorone

Cited by 58 publications

References 9 publications

Heterogeneously Catalyzed Asymmetric Hydrogenation of C═C Bonds Directed by Surface-Tethered Chiral Modifiers

Heterogeneously Catalyzed Asymmetric Hydrogenation of C═C Bonds Directed by Surface-Tethered Chiral Modifiers

Nature of Proline-induced Enantiodifferentiation in Asymmetric Pd Catalyzed Hydrogenations: Is the Catalyst Really Indifferent?

Diastereoselective Catalysis

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