Abstract
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 α-Tfm-phenylalanine (R)-8 (with regeneration and recycling the chiral auxiliary), α-Tfm-leucine (S)-11e, α-Tfm-butyrine (S)-11f and α-Tfm-alanine (S)-11g in two steps in one-pot. SCV1
Published Version
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