(Rc,Ss)-1,1,1-trifluoro-3-(p-tolysulfinyl)-2-propanol (>99% e.e.), an important reagent for the asymmetric protonation of substituted enolates, was prepared (70%) from (S)-methyl p-tolyl sulfoxide. The stereoselectivity of the Yamdazyma farinosa-catalyzed reduction of carbonyl groups, the key step for the introduction of an asymmetric carbon, was greatly affected by the stereochemistry of the asymmetric sulfur atom. The reduction of (S)-1,1,1-trifluoro-3-(p-tolylsulfinyl)-2-propanone proceeded smoothly and in a quite stereoselective manner to give the desired compound, while a 76 : 24 mixture of (Rc,Rs)-and (Sc,Rs)-isomers was obtained from the substrate with the opposite (R)-configuration.
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