Diastereoselective hydrogenation of o-toluic acid derivatives over supported rhodium and ruthenium heterogeneous catalysts

Бессон, М.; Neto, Samuel; Pinel, Catherine

doi:10.1039/a802822b

Cited by 43 publications

(20 citation statements)

References 5 publications

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“…The selectivity in the hydrogenation of 12d was high with the ruthenium catalyst and only slightly lower than that obtained with the rhodium catalysts [88].…”

Section: Diastereoselective Hydrogenation Of Substituted Aromaticsmentioning

confidence: 77%

“…Further complications arose because the substrate 12a may exist in two atropisomeric forms, which may hydrogenate with different diastereoselectivity [89]. In contrast, 12d was prepared selectively in one of its atropisomeric forms [88]. The excellent diastereoselectivity obtained in the hydrogenation of 12d over the alumina-supported catalyst (N) was attributed to a stronger interaction of the substrate, with incompletely reduced rhodium, higher steric constraints owing to the flat morphology of rhodium particles and the interaction of the substrate with alumina upon adsorption [90].…”

Section: Diastereoselective Hydrogenation Of Substituted Aromaticsmentioning

confidence: 99%

“…Besson et al made a thorough study of the diastereoselective hydrogenation of o-toluic acid coupled to many different types of proline auxiliaries [85][86][87][88]. Hydrogenation reactions were conducted at room temperature in alcoholic solvents and at 50 bar hydrogen pressure over either carbon-or aluminasupported rhodium catalysts.…”

Section: Diastereoselective Hydrogenation Of Substituted Aromaticsmentioning

confidence: 99%

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Diastereoselective Hydrogenation in the Preparation of Fine Chemicals

Kukula¹,

Prins

2004

ChemInform

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“…The selectivity in the hydrogenation of 12d was high with the ruthenium catalyst and only slightly lower than that obtained with the rhodium catalysts [88].…”

Section: Diastereoselective Hydrogenation Of Substituted Aromaticsmentioning

confidence: 77%

Section: Diastereoselective Hydrogenation Of Substituted Aromaticsmentioning

confidence: 99%

Section: Diastereoselective Hydrogenation Of Substituted Aromaticsmentioning

confidence: 99%

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Diastereoselective Hydrogenation in the Preparation of Fine Chemicals

Kukula¹,

Prins

2004

ChemInform

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“…The best facial differentiation was achieved using methyl pyroglutamate [111]. The resulting substrate possesses two most stable conformations, as calculated by molecular modeling with a very small energy difference (1 kJ mol −1 ) and a very large interconversion barrier (>1000 kJ mol −1 ), which indicated that there is no possible interconversion between these two conformers [112].…”

Section: Diastereoselective Hydrogenation Of Aromatic Ringsmentioning

confidence: 96%

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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“…[17] We recently reported [18] that high selectivities ( 95 %) could be achieved by the use of (S)-pyroglutamic acid methyl ester as the chiral auxiliary. The present study was designed to provide a better understanding of the origin of the asymmetry in this reaction.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Synthesis of 2-Methyl Cyclohexane Carboxylic Acids by Heterogeneous Catalysis: Mechanistic Aspects

et al. 2000

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The catalytic hydrogenation of (S)-alkyl-N-(2-methylbenzoyl)pyroglutamates was studied over supported rhodium and ruthenium catalysts at room temperature and a pressure of 5 MPa. The reaction was diastereoselective with the predominant formation of (1S,2R)-2-methylcyclohexane carboxylic acid with a diastereomeric excess (de) of up to 96%. The most stable conformation was determined by means of a combination of modelling calculations, NMR spectroscopy and X-ray structural determination. In this conformation, the carbonyl group of the pyroglutamate auxiliary shields one face of the aromatic ring. The observed selectivity may thus be explained by a preferential adsorption at the unshielded face which avoids steric repulsion by the C=O group to result in a cis hydrogenation. The addition of an amine, the nature of the support (alumina or active carbon) or of the metal (Rh or Ru) were shown to give additional stabilisation of the adsorption at the unshielded face to increase the diastereoisomeric excess.

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Diastereoselective hydrogenation of o-toluic acid derivatives over supported rhodium and ruthenium heterogeneous catalysts

Cited by 43 publications

References 5 publications

Diastereoselective Hydrogenation in the Preparation of Fine Chemicals

Diastereoselective Hydrogenation in the Preparation of Fine Chemicals

Diastereoselective Catalysis

Asymmetric Synthesis of 2-Methyl Cyclohexane Carboxylic Acids by Heterogeneous Catalysis: Mechanistic Aspects

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