We have developed intramolecular [2+2] photocycloaddition of styrene derivatives, such as substituted styrene, vinylnaphthalene, vinyiphenanthrene, and so on. The photocyclization showed tether-length dependency ; i.e., the longer the tether becomes, the lower yield is obtained. If oligo(oxyethylene) linkage is used as the tether, however, the yield does not depend on the length and generally becomes quantitative. This tendency has been determined to be due to the flexible property of oligo(oxyethylene) chain.
We were prompted to use this efficient reaction to make a new type of crown compounds (so- called crownophanes) and succeeded in the cultivation of a new ionophore synthetic method.
The prototypical crownophanes showed relatively high Li^+ ion selectivity on the solid-liquid extraction, so we tried to improve the selectivity and found, after several trials, that simply and appropriately modified crownophanes having two cyclobutane linkages (crownopaddlanes) extracted the Li ion exclusively and quantitatively on the extraction experiment.
Next we tried to make crownophanes working efficiently for the extraction of heavy metal cations. We first made some precursors having two hydroxyl groups on the oligo(oxyethylene) linkage or the aromatic nuclei and then treated these functional groups with pyridylmethyl chloride. The modified crownophanes with two pyridine side arms showed high affinity toward Ag^+ ion on the liquid-liquid extraction. Especially, the compound having the side arms on the aromatic nuclei exhibited the excellent selectivity.