The reaction of secondary α-amino acids with carbonyl compounds. Properties of the intermediate azomethine ylides. Oxazolidine formation versus 1.4-prototropy.

Abstract

Cyclic secondary α-amino acids react regiospecifically, via antidipole formation, with aldehydes bearing electron withdrawing substituents to give oxazolidines in good yield. In certain cases structural features in the α-amino acid promote a 1,4-prototropic process in the intermediate azomethine ylide and divert the reaction to give 2-pyrrolines, whilst use of ninhydrin as the carbonyl component results, in favourable cases, in stable azomethine ylides.