Metal-free activation of C–C multiple bonds through halide ion pairs: Diels–Alder reactions with subsequent aromatization

Imidazolium and ammonium halides, both in homogeneous phase or immobilized on mesoporous silica, proved able to promote the aromatization reaction of Diels–Alder adducts under ethylene and H2 elimination. These observations point to the increased nucleophilicity of such halide ions. They also open the possibility to employ such ion pairs as nucleophilic organocatalysts, for example, as substitutes for phosphines or amines.