Synthesis of optically active azetidine-2,4-dicarboxylic acid and related chiral auxiliaries for asymmetric synthesis

(S)-1-Phenylethylamine has been used as a chiral auxiliary as well as a nitrogen atom donor in the synthesis of an enantiomeric pair of azetidine-2,4-dicarboxylic acids, the absolute configuration of one of which has been assigned on the basis of the X-ray structure and the known absolute configuration of the (S)-1-phenylethylamine moiety. Chiral auxiliaries of related C2-symmetric azetidines have also been prepared and their propionamides have been asymmetrically alkylated. The stereochemistry of the resulting products was compared with their analogues having different ring sizes.