Rational Design of Diels-Alder Catalysts

Significance

Non-coordinating anions are widely used in cationic catalysts for Diels-Alder reactions to enhance the reactivity. However, the use of labile cationic catalysts is often accompanied with side reactions, product inhibition, and catalyst decomposition. In this paper the authors suggest a way to overcome these issues by the use of weak secondary interactions to stabilize the cationic species. Thus, heteroatoms Y can displace counterions X, leading to equilibrium between species A and B. In order to avoid the equilibrium, protic HZ moieties can be used to displace counterions with their subsequent stabilization. This approach proved to be highly efficient in system 1: NHMs groups were dramatically superior to the analogues with OMe and OAc substituents. The proposed interaction picture was supported by theoretical calculations.