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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
Auteur(s)
Vallat, Oliver
Buciumas, Ana-Maria
Date de parution
2009
In
Journal of Chemical Crystallography, Published Version ; http://dx.doi.org/10.1007/s10870-009-9596-y, 2009/40/1/10-14
Résumé
The title compounds, rac-(2R*,3R*)-S-ethyl-4-chloro-3-hydroxy-2-phenylbuthanethioate (<b>I</b>) and rac-(2R*,3R*)-S-ethyl-2-phenyl-3-(tosyloxy)buthanethioate (<b>III</b>), are both composed of a S-ethyl 2-phenylbutanethioate moiety but have different geometries. Compound <b>I</b> is substituted in the 3 and 4 positions by a hydroxyl group and a chlorine atom, respectively. In compound <b>III</b> the hydroxyl group in the 3 position of rac-(2R*,3R*)-S-ethyl-3-hydroxy-2-phenylbuthanethioate (<b>II</b>), has been tosylated in order to obtain suitable crystals for X-ray analysis. In compound <b>I</b> the phenyl substituent and the hydroxyl group have a <i>syn</i> arrangement, whereas in the tosylate derivative of <b>II</b>, i.e., compound <b>III</b>, they have an <i>anti</i> arrangement. In the crystal structure of <b>I</b> 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 <b>III</b> 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 <b>I</b>) and acetaldehyde (for <b>II</b>). The <i>syn/anti</i> stereo descriptors clearly indicate that the stereoselectivity of the Mukaiyama aldol reaction has switched from a <i>syn</i> selective process for the reaction using 2-chloroacetaldehyde to an <i>anti</i> 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.
Identifiants
Type de publication
journal article
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