Stereoselective reactions of chiral α-amino aldehydes

Optically active α-amino acids can be converted into the corresponding doubly protected N,N-dibenzyl α-amino aldehydes. These react diastereoselectively with Grignard reagents, lithium enolates and Me3SiCN/ZnX2 to provide the nonchelation-controlled adducts. Molecular modelling explains some of the results. The sense of stereoselectivity can be reversed if Lewis acidic chelating reagents are used. Undesired racemization does not occur.