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Rac-(2R*,3R*)- S -Ethyl-4-Chloro-3-Hydroxy-2-Phenylbuthanethioate and Rac-(2R*,3R*)- S -Ethyl-2-Phenyl-3-(tosyloxy)buthanethioate: Dichotomy of the Stereoselectivity of the Mukaiyama Reaction

Vallat, Oliver ; Buciumas, Ana-Maria ; Neier, Reinhard ; Stoeckli-Evans, Helen

In: Journal of Chemical Crystallography, 2010, vol. 40, no. 1, p. 10-14

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    Titre
    • Rac-(2R*,3R*)- S -Ethyl-4-Chloro-3-Hydroxy-2-Phenylbuthanethioate and Rac-(2R*,3R*)- S -Ethyl-2-Phenyl-3-(tosyloxy)buthanethioate: Dichotomy of the Stereoselectivity of the Mukaiyama Reaction
    Auteur
    • Vallat, Oliver. Institute of Chemistry, University of Neuchâtel, rue Emile-Argand 11, 2009, Neuchâtel, Switzerland
    • Buciumas, Ana-Maria. Institute of Chemistry, University of Neuchâtel, rue Emile-Argand 11, 2009, Neuchâtel, Switzerland
    • Neier, Reinhard. Institute of Chemistry, University of Neuchâtel, rue Emile-Argand 11, 2009, Neuchâtel, Switzerland
    • Stoeckli-Evans, Helen. Institute of Physics, University of Neuchâtel, rue Emile-Argand 11, 2009, Neuchâtel, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Journal of Chemical Crystallography, 2010, vol. 40, no. 1, p. 10-14. Springer US; http://www.springer-ny.com
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:315575
    Summary
    The title compounds, rac-(2R*,3R*)-S-ethyl-4-chloro-3-hydroxy-2-phenylbuthanethioate (I) and rac-(2R*,3R*)-S-ethyl-2-phenyl-3-(tosyloxy)buthanethioate (III), are both composed of a S-ethyl 2-phenylbutanethioate moiety but have different geometries. Compound I is substituted in the 3 and 4 positions by a hydroxyl group and a chlorine atom, respectively. In compound III the hydroxyl group in the 3 position of rac-(2R*,3R*)-S-ethyl-3-hydroxy-2-phenylbuthanethioate (II), has been tosylated in order to obtain suitable crystals for X-ray analysis. In compound I the phenyl substituent and the hydroxyl group have a syn arrangement, whereas in the tosylate derivative of II, i.e., compound III, they have an anti arrangement. In the crystal structure of I centrosymmetric hydrogen bonded dimers are formed via O-H···O hydrogen bonds, involving the hydroxyl group and the carbonyl O-atom. In the crystal structure of III symmetry related molecules are connect via a weak C-H···O intermolecular interaction, involving a tosylate O-atom and a phenyl H-atom, so forming zigzag chains propagating in the c direction. The compounds were prepared by the Mukaiyama crossed aldol reaction between the silyl enol ether of S-ethyl 2-phenylethanethioate and simple aldehydes, like 2-chloroacetaldehyde (for I) and acetaldehyde (for II). The syn/anti stereo descriptors clearly indicate that the stereoselectivity of the Mukaiyama aldol reaction has switched from a syn selective process for the reaction using 2-chloroacetaldehyde to an anti selective process for the reaction with acetaldehyde. In both compounds the relative stereochemistry at the newly created chiral centers, positions 2 and 3, is R/R. Graphical Abstract: The compounds, rac-(2R*,3R*)-S-ethyl-4-chloro-3-hydroxy-2-phenylbuthanethioate (I) and rac-(2R*,3R*)-S-ethyl-3-hydroxy-2-phenylbuthanethioate (II), were prepared by the Mukaiyama crossed aldol reaction between the silyl enol ether of S-ethyl 2-phenylethanethioate and simple aldehydes, like 2-chloroacetaldehyde (for I) and acetaldehyde (for II). The stereoselectivity of the Mukaiyama aldol reaction was shown to have switched from a syn selective process for the reaction using 2-chloroacetaldehyde to an anti selective process for the reaction with acetaldehyde