Enolate chemistry with anion–π interactions

Anion–π interactions occur on the surface of π-acidic aromatic planes with positive quadrupole moments. Their ability to contribute to the binding and transport of anions has been demonstrated recently. However, their ability to stabilize anionic reactive intermediates and transition states remains essentially unexplored. This situation is contrary to the recognized importance of the complementary cation–π interactions to catalyse most important reactions in biology and chemistry. In this report, we provide direct experimental evidence that already single unoptimized anion–π interactions can stabilize enolates by almost two pKa units. The addition of these anion-π-stabilized reactive enolate intermediates to enones and nitroolefins occurs with transition-state stabilizations of up to 11 kJ mol−1, and anionic cascade reactions accelerate on π-acidic surfaces. These findings are significant because enolate chemistry is central in chemistry and biology, and they will stimulate the use of anion-π interactions in catalysis in the broadest sense.