Synthesis of crownophanes possessing three pyridine rings

Novel crownophanes with three pyridine moieties (pyridinocrownophanes 4 and 5) were prepared by means of intramolecular [2+2] photocycloaddition of vinylpyridine derivatives. In the liquid-liquid extraction of heavy metal cations, 4 and 5 exhibited high efficiency toward Ag+. Comparing the high extractability and complexing stability constant for Ag+ to those of the corresponding pyridinocrownophanes 2 and 3 and observing the 1H NMR spectra in the presence of Ag+, the ethereal oxygen atoms and the three nitrogen atoms were found efficiently and cooperatively to act as ligating sites.