Stereoselective addition of organometallic reagents to a chiral acyclic nitrone derived from l-erythrulose

The additions of various organolithium and organomagnesium reagents to a chiral nitrone prepared from l -erythrulose took 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 acid additives: zinc bromide enhances the attack to the Si face of the C N bond whereas diethyl aluminium chloride promotes attack to the Re face. The obtained adducts can be then transformed into protected N -hydroxy-α,α-disubstituted-α-amino acid derivatives as well as into the corresponding α,α-disubstituted α-amino acids.