Two act as one: unexpected dimers of catechol direct a solid-state [2+2] photodimerization in a six-component hydrogen-bonded assembly

We describe hydrogen-bonded dimers of catechol that act collectively as a single template to direct an intermolecular [2+2] photocycloaddition in the solid state. The directed reactivity involves discrete, six-component hydrogen-bonded assemblies and a photoreaction that occurs stereoselectively and in quantitative yield.