Rim-Differentiated C 5‑Symmetric Tiara-Pillar[5]arenes

The synthesis of “rim-differentiated” C 5-symmetric pillar­[5]­arenes, whose two rims are decorated with different chemical functionalities, has remained a challenging task. This is due to the inherent statistical nature of the cyclization of 1,4-disubstituted alkoxybenzenes with different substituents, which leads to four constitutional isomers with only 1/16th being rim-differentiated. Herein, we report a “preoriented” synthetic protocol based on FeCl3-catalyzed cyclization of asymmetrically substituted 2,5-dialkoxybenzyl alcohols. This yields an unprecedented 55% selectivity of the C 5-symmetric tiara-like pillar[5]­arene isomer among four constitutional isomers. Based on this new method, a series of functionalizable tiara-pillar[5]­arene derivatives with C 5-symmetry was successfully synthesized, isolated, and fully characterized in the solid state.