Ring Contraction in Schiff Base Macrocycles: the X-Ray Crystal Structure of an Imidazolidine-Containing Macrocycle

Cyclocondensation of benzene-1,3-dicarbaldehyde and 3-azapentane-1,5-diaminein acetonitrile leads to isolation of an 18-membered imidazolidine-containing Schiff base macrocycle rather than the anticipated 24-membered tetraimine Schiff base macrocycle. This has occurred as a consequence of internal nucleophilic addition of the secondary amine functions across adjacent azomethine bonds. The X-ray crystal structure of the imidazolidine-containing Schiff base macrocycle is reported.