Supramolecular-Induced Regiocontrol over the Photochemical [4+4] Cyclodimerization of NHC- or Azole-Substituted Anthracenes

Thanks to the impressive control that microenvironments within enzymes can have over substrates, many biological reactions occur with high regio- and stereoselectivity. However, comparable regio- and stereoselectivity is extremely difficult to achieve for many types of reactions, particularly photochemical cycloaddition reactions in homogeneous solutions. Here, we describe a supramolecular templating strategy that enables photochemical [4 + 4] cycloaddition of 2,6-difunctionalized anthracenes with unique regio- and stereoselectivity and reactivity using a concept known as the supramolecular approach. The reaction of 2,6-azolium substituted anthracenes H4-L(PF6)2 (L = 1a–1c) with Ag2O yielded complexes anti-[Ag2L2](PF6)4 featuring an antiparallel orientation of the anthracene groups. Irradiation of complexes anti-[Ag2L2](PF6)4 proceeded under [4 + 4] cycloaddition linking the two anthracene moieties to give cyclodimers anti-[Ag2(2)](PF6)2. Reaction of 2,6-azole substituted anthracenes with a dinuclear complex [Cl-Au-NHC–NHC-Au-Cl] yields tetranuclear assemblies with the anthracene moieties oriented in syn-fashion. Irradiation and demetallation gives a [4 + 4] syn-photodimer of two anthracenes. The stereoselectivity of the [4 + 4] cycloaddition between two anthracene moieties is determined by their orientation in the metallosupramolecular assemblies.