Photocycloaddition of Chalcones to Yield Cyclobutyl Ditopic Cyclophanes

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