Catalyst, Base, Additives, and Solvent: The Tools to Dig a Better CANAL Reaction

The Catalytic Arene Norbornene Annulation (CANAL) reaction has been established as an effective method for the preparation of norbornene-cyclobutenyl-arene products. To expand the scope of this reaction to encompass sensitive substrates, such as ones which will provide next generation polyacene dimers, we herein report the development of a CANAL protocol through a parallel experimentation approach, aiming to reduce the temperature of the reaction. This was accomplished through exploration and modification of the catalyst-ligand system, base, solvent, and concerted metalation-deprotonation (CMD) promoters, providing conditions with typical temperatures of 70 °C and as low as 60 °C with some substrates. Through these studies, we have discovered reliable conditions for aryl bromides, chlorides, and triflates. In addition, we have demonstrated the utility of these conditions through preparation of a novel anthracene dimer, TIPS-BAS, which could not be prepared using literature conditions.