Role of Aromatic Interactions in Directing Organic Reactions
Non-covalent interactions involving aromatic rings abound in organic reactions, impacting everything from molecular structure and stability to catalytic activity and stereoselectivity. Following a brief overview of the relevant aromatic interactions (π-stacking interactions, CH/π interactions, anion–π interactions, and π–π+ interactions), we describe representative examples of catalytic and non-catalytic organic reactions in which aromatic interactions serve as key control elements. First we describe non-catalytic reactions, including examples of cycloadditions and macrocyclizations, followed by discussions of transition-metal catalyzed CH-activations, asymmetric hydrogenations, and oxidations. Next, we provide an overview of organocatalytic reactions in which aromatic interactions play key roles, including examples of enamine and iminium catalysis, N-heterocyclic carbene catalysis, Brønsted-acid catalysis, and hydrogen-bonding catalysis, followed by examples of cooperative catalysis in which aromatic interactions have been shown to play key roles. Finally, we discuss reactions controlled by anion–π and π–π+ interactions.