Synthesis of α,α-Disubstituted α-Amino Acid Derivatives in Enantiopure Form via Stereoselective Addition of Grignard Reagents to a Chiral Acyclic Nitrone Derived from L-Erythrulose

Abstract

The additions of various Grignard reagents to a chiral nitrone prepared from l-erythrulose take place with variable dia­stereoselectivity. The degree and strength of the facial selectivity can be modified if the reaction is performed in the presence of Lewis acidic additives: zinc bromide enhances attack to the si face whereas diethyl aluminum chloride promotes attack to the re side. The obtained adducts can be then efficiently transformed into protected N-hydroxy α,α-disubstituted α-amino acid derivatives as well as into the corresponding α,α-disubstituted α-amino acids.