A simple approach towards shape-persistent nanoscale pyridine macrocycles

Two new shape-persistent macrocycles with intraannular pyridine groups are described. The cyclization is performed by an intermolecular oxidative acetylene dimerization of two “half-rings” which is prepared by Pd-catalyzed aryl acetylene coupling reactions. In both cases the ring building blocks are synthesized from pyrylium salts, either by treating with sodium pyridyl acetate or with ammonia. One macrocycle could be crystallized from pyridine as a solvate. It adopts a cyclohexane-like chair conformation in which the empty space inside the rings hosts the solvent molecules.