A broadening of the investigation of the ring–chain tautomeric process of N-substituted 1,3-X,N-heterocycles (X = O, S, NR) to Se containing macrocyclic compounds allowed the isolation and structurally solid state characterization of the cyclic tautomer 7, which due to the length of the aliphatic chain, is able to form a stable six-membered ring (6-endo-trig). The theoretical calculations based on the DFT method (Gaussian 03 software package) also support the fact that tautomer 7 is more stable than the chain tautomer 6. Thus, based on the ring–chain tautomerism of the macrocycles that contain alkyl chains with amino–imino, imino–alcohol or sulphur–imino groups, combined with a strategy that allows the formation of a stable six-membered ring, the main reaction products will be the cyclic tautomers. The ring–chain equilibria of these macrocycles could be exploited advantageously in different areas of macrocyclic, physical and medicinal chemistry in order to obtain compounds with practical applications.