Lone Pair−π Interactions in Organic Reactions

Abstract

Noncovalent interactions between a lone pair of electrons and π systems can be categorized into two types based on the nature of π systems. Lone pair−π(C═O) interactions with π systems of unsaturated, polarized bonds are primarily attributed to orbital interactions, whereas lone pair−π(Ar) interactions with π systems of aromatic functional groups result from electrostatic attractions (for electron-deficient aryls) or dispersion attractions and Pauli repulsions (for electron-rich/neutral aryls). Unlike well-established noncovalent interactions, lone pair−π interactions have been comparatively underappreciated or less used to influence reaction outcomes. This review emphasizes experimental and computational studies aimed at integrating lone pair−π interactions into the design of catalytic systems and utilizing these interactions to regulate the reactivity and selectivity of chemical transformations. The role of lone pair−π interactions is highlighted in the stabilization or destabilization of transition states and ground-state binding. Examples influenced by lone pair−π interactions with both unsaturated, polarized bonds and aromatic rings as π systems are included. At variance with previous reviews, the present review is not structured according to the physical origin of particular classes of lone pair−π interactions but is divided into chapters according to ways in which lone pair−π interactions affect kinetics and/or selectivity of reactions.