New Syntheses and Physical Properties of p-Alkylcalix[n]arenes

Calix[n]arenes (n=4, 6, and 8) bearing long p-alkyl groups (R=hexyl and dodecyl) have been synthesized by “direct” acylation of the p-position followed by silane reduction. The method is convenient and the yields are higher than those reported so far. Among them, p-hexanoylcalix[4]arene showed a curious phase transition behavior; with raising the temperature it changed as crystal A→liquid→crystal B→liquid. It was found on the basis of the solid 13CNMR spectra that this behavior is ascribed to a conformational change from “cone” (crystal A) to “partial cone” (crystal B).