Asymmetric synthesis of quaternary alpha-amino acids using D-ribonolactoneacetonide as chiral auxiliary

We describe a new simple methodology to prepare enantiopure alpha,alpha-dia lkylglycines based on the use of commercially available D-ribonolactone as a chiral auxiliary. Enantiopure alpha-methyl and alpha-butyl series are pre pared through diastereoselective alkylation and subsequent Schmidt rearrang ement of alpha,alpha-dialkylacetoacetates of D-ribonolactone acetonide. Abs olute configuration was assigned through preparation of enantiopure 4,4-dis ubstituted 3-methyl-2-pyrazolin-5-ones. (C) 1999 Elsevier Science Ltd. All rights reserved.