Novel bicyclic chiral crown ethers having a p-xylenedioxy unit with improved complex stability and rate-enhancement in the intra-complex thiolysis of α-amino acid ester salts

Novel bicyclic chiral crown ethers having an a, al-p-xylenedioxy unit were synthesized. Crown dithiol 1 with a p-xylenedioxy bridge-structure performed intra-complex thiolysis with a-amino acid p-nitrophenyl ester HBr salts much faster than the corresponding dithiol 3 without the bridge-structure. A ¹H-NMR study suggested that the increased rate of intra-complex thiolysis is due to increased stability of the intermediary complex during the reaction.