Synthesis of a Ditopic Cyclophane Based on the Cyclobutane Ring by Chalcone Photocycloaddition

The intramolecular photocycloaddition of chalcones to give cyclobutanes has proven to be a fast and simple method to shrink a cyclophane ring to a tricyclic system, in order to prepare potential ditopic receptors. In particular, the chalcone I, having dioxyethylene chains as spacers, is converted in high yield to the cyclobutane II. NOESY spectroscopy indicates that the formation of II occurs by a head-to-head syn ring closure.