Asymmetric Synthesis of Quaternary a-Amino Acids Using D-Ribonolactone Acetonide as a Chiral Auxiliary

Preparation of a,a -disubstituted glycines is a matter of current interest owing to their importance as enzyme inhibitors and peptide modifiers. Herein, we describe a new simple methodology to prepare enantiopure a,a -dialkylglycines based on the use of commercially available D-ribonolactone as chiral auxiliary. Enantiopure a -methyl and a -butyl series are prepared through diastereoselective alkylation and posterior Schmidt rearrangement of a,a -dialkylacetoacetates of D-ribonolactone acetonide. Absolute configuration was assigned through preparation of enantiopure 4,4-disubstituted 3-methyl-2-pyrazolin-5-ones