Kosuke Kawada

New asymmetric approach to β-trifluoromethyl isoserines

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.

Methyl NFSI: atom-economical alternative to NFSI shows higher fluorination reactivity under Lewis acid-catalysis and non-catalysis

Me-NFSI was first reported in 1994. Despite its atom-economical structure and similarity to a well-explored fluorinating reagent, NFSI, Me-NFSI has not appeared in the literature in over 20 years. We disclose that Me-NFSI is more effective for the fluorination of active methines under Lewis acid-catalysis and non-catalysis than NFSI.