Synthetic potential of heteroatomic ring systems

The synthesis of aziridine-2-carboxylic acid derivatives of high enantiopurity is described and their synthetic utility is discussed. Ring-opening and ring-expansion reactions of both oxirane and aziridine carboxylic esters are highlighted. Convenient syntheses of alpha-hydroxy, beta-amino and alpha-amino, beta-hydroxy carboxylic acids with defined stereochemistry are presented. The presentation of pyrrolidinone and azetidinone derivatives from functionalized three-membered heterocycles is described. Small-ring heterocycles also serve as the basis for the synthesis of catalysts, e.g. for an asymmetric reduction and for cyclopropanation reactions.