Epimerization of Diastereomeric α-Amino Nitriles to Single Stereoisomers in the Solid State

A diastereomeric mixture of the α-amino nitrile prepared by the Strecker reaction of benzaldehyde, (1S,2R)-1-aminoindan-2-ol, and cyanotrimethylsilane thermally epimerizes in the solid state to give a single diastereomer with an (S)-configuration at the α position to the nitrile moiety. This shows a sharp contrast to the reaction conducted in DMSO at room temperature, which gives a 1:1 mixture of (S)- and (R)-isomers. Several other α-amino nitriles also epimerize in the solid-state toward single diastereomers.