Decamethyl-pillar[5]arene: Synthesis and Recognition Properties

In this two-session experiment for an organic chemistry lab, students prepare a macrocyclic host compound─namely, a pillar[5]arene─by means of a templated 1,4-dimethoxybenzene/formaldehyde cyclo-oligomerization (session 1), and then, they explore its molecular recognition properties toward the 1,8-diaminooctane guest with the aid of 1H NMR spectroscopy (session 2). The acid-catalyzed synthesis of decamethyl-pillar[5]arene provides, in good yield, a product sufficiently pure to be directly used in the subsequent NMR titration experiment. The two-session experiment targets advanced chemistry students, whereas the 4 h synthesis of the macrocycle (session 1) may be included in an introductory organic chemistry laboratory course. This experiment links concepts spanning from classical SEAr reactions to macrocycle synthesis down to host-guest chemistry, NMR spectroscopy, and data treatment, providing a useful connection between organic chemistry synthesis and supramolecular chemistry.