Highly Stereoselective Aldol Reactions By Memory Of Chirality: Synthesis Of Quaternary Beta-Hydroxy Alpha-Amino Acids

We describe here an asymmetric aldol reaction based on the principle of Memory of Chirality. From alpha-amino acids such as leucine and methionine, we have synthesized in two steps quaternary alpha-amino acid derivatives with high diastereoselectivity and enantioselectivity, using the chirality of the initial alpha-amino acid as the only chirality source. Furthermore, we were able to determine the relative and absolute configurations of the aldol products thanks to crystallographic structures and thus showed that the relative configuration depended on the aldehyde employed. We proposed a stereoselectivity explanation and obtained also quaternary beta-hydroxy alpha-amino acids after acidic hydrolysis.