ChemInform Abstract: Influence of the Nature of Chiral Auxiliaries on the Diastereoselective Hydrogenation of ortho‐Substituted Benzoic Acid Derivatives.

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

doi:10.1002/chin.200039053

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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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Section: Introductionmentioning

confidence: 99%