Diastereospecific photochemical dimerization of a stilbene-containing daisy chain monomer in solution as well as in the solid state

A crown ether/dialkylammonium ion hybrid containing a stilbene group self-assembles into a [c2]daisy chain-like pseudorotaxane, the solid-state superstructure of which was confirmed by X-ray crystallography. Upon irradiation, the pseudorotaxane undergoes an efficient photochemical [2+2] dimerization, both in solution as well as in the solid state, to yield one cyclobutane diastereoisomer with syn-anti-syn stereochemistry and head-to-tail regiochemistry (see scheme).