Exploiting the p‑Bromodienone Route for the Formation and Trapping of Calixarene Oxenium Cations with Enamine Nucleophiles

This study shows that calixarene p-bromodienone derivatives can act as precursors for the formation of oxenium cations, which can be trapped with enamine C-nucleophiles. When calixarene p-bromodienones were treated with enamines, in the presence of AgClO₄, the lower rim-substituted C–O–C products were obtained by an electrophilic attack of the intermediate calixarene-oxenium cation with a contemporary cone-to-partial-cone inversion of the involved aromatic ring.