New asymmetric approach to β-trifluoromethyl isoserines

Abstract

Enantiomerically pure N,O-protected β-trifluoromethyl isoserine derivatives of (2S,3S)- and (2R,3S)-absolute configurations have been easily prepared by diastereoselective addition of the enolates, derived from O-protected α-hydroxyacetates, to (S)-N-tert-butanesulfinyl (3,3,3)-trifluoroacetaldimine with high combined yield and good syn/anti stereoselectivity. To explain the unusual stereochemical outcome in these reactions a mechanistic rationale involving the addition of Z-enolates to (S)-imines via open transition states was proposed on the basis of the experimental data. Elaboration of these products via chemoselective manipulation of the protecting groups has been demonstrated.