An improved large scale synthesis of the Schollkopf chiral auxiliaries:: (2R)- and (2S)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine

Syntheses of the Schollkopf 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.