On the Conformational Isomers in Tetra-O-alkylcalix[4]arenes

Abstract p-t-Butylcalix[4]arene (14H) was alkylated with RX (R = Me, Et, Pr, and Bu) and the products (14R) were analyzed by HPLC and 1H NMR. It was found that (i) ring inversion arising from the oxygen-through-the-annulus rotation can be inhibited by R greater than Et, (ii) “cone” and “partial cone” result in a 1:1 ratio, and (iii) thermodynamically, the “partial cone” conformation is most stable.