Sulfinimines of trifluoropyruvate: Novel intermediates for chiral non racemic α-trifluoromethyl α-amino acids

Article abstract of DOI:10.1016/S0040-4039(98)01698-0

A new and preparatively useful method for the synthesis of non racemic α-trifluoromethyl (Tfm)α-amino acids (AAs) is presented. Key-building blocks are the sulfinimines (S)-1a,b, prepared via Staudinger reaction from trifluoropyruvic esters and the chiral N-sulfinyl iminophosphorane (S)-5, which were reacted with benzyl and alkylmagnesium halides. The resulting N- sulfinyl α-Tfm α-amino esters 6a,b and 6c-g, respectively, were produced with opposite stereoselectivity. The stereocontrol with alkyl Grignard reagents was progressively higher with increasing steric bulk. Some of the adducts 6 were transformed into a-Tfm-phenylalanine (R)-8 (with regeneration and recycling the chiral auxiliary), αTfm-leucine (S)-11c, α-Tfm-butyrine (S)-11f and α-Tfm-alanine (8),11g in two steps in one-pot.