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 complexesanti-[Ag₂L₂](PF₆)₄featuring an antiparallel orientation of the anthracene groups. Irradiation of complexesanti-[Ag₂L₂](PF₆)₄proceeded under [4 + 4] cycloaddition linking the two anthracene moieties to give cyclodimersanti-[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 insyn-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.