New fast and practical method for the enantioselective synthesis of α-vinyl, α-alkyl quaternary α-amino acids

We describe a fast and practical enantioselective synthesis of (S)-N-Cbz-a-vinyl, phenylalanine, suitable for the preparation of different N-Cbz-a-vinyl aminoacids of both configurations. The new protocol exploits a Wittig reaction on highly enantiomeric enriched N-Cbz-a-formyl-a-alkyl amino esters, readily accessible from (L)-serine through a stereoselective alkylation of Seebach’s oxazolidine, carried out with a significant improvement of the previously reported method. The synthetic scheme is suitable for gram scale preparation of the desired product with a 94% ee