Photocycloaddition of chalcones to yield cyclobutyl ditopic cyclophanes

The intramolecular photocycloaddition of chalcones to give cyclobutanes has proved to be a fast and convenient method to shrink a cyclophane ring to a tricyclic system, in order to prepare potential ditopic receptors. X-Ray results confirm the previously indicated structure for the cyclobutanes (n=1, m=1), in which the cyclization occurs by a head-to-head syn ring closure. NMR results indicate that the same process occurs for the cyclobutanes (n=2, m=2) and (n=1, m=3).