An Improved Large Scale Synthesis of the Schöllkopf Chiral Auxiliaries: (2R)- and (2S)-2,5-Dihydro-3,6-dimethoxy-2-isopropylpyrazine

Syntheses of the Schöllkopf chiral auxiliaries have been carried out on large scale in high overall yields from d- and l-valine. This method avoids the use of highly toxic phosgene or triphosgene, low-temperature reactions, and unstable intermediates.