Supramolecular photochemical synthesis of an unsymmetrical cyclobutane.

2-styrylbenzothiazole (1) and cinnamic acid (2) derivatives containing 15-crown-5 ether moieties form a supramolecular assembly in the presence of Ba(2+) cations in acetonitrile. The assembly is stabilized by hydrogen bonding between the heterocyclic N atom of 1 and the proton of the carboxylic group of 2, by sandwich Ba(2+) complex formation between the crown ether moieties of 1 and 2, and by pi-pi stacking interactions. Irradiation of solutions containing these supramolecular complexes leads to highly specific formation of an unsymmetrical cycloadduct. This investigation provides an interesting example of supramolecular control of [2 + 2]-photocyclization in solution.