Asymmetric synthesis of quaternary α-amino acids using D-ribonolactone acetonide as chiral auxiliary

We describe a new simple methodology to prepare enantiopure α,α- dialkylglycines based on the use of commercially available D-ribonolactone as a chiral auxiliary. Enantiopure α-methyl and α-butyl series are prepared through diastereoselective alkylation and subsequent Schmidt rearrangement of α,α-dialkylacetoacetates of D-ribonolactone acetonide. Absolute configuration was assigned through preparation of enantiopure 4,4- disubstituted 3-methyl-2-pyrazolin-5-ones.