Structural Effects of the Per-O-Acetylation Reaction on Calix[4]Resorcinarenes: New Perspectives

In the present article, tetra(nonyl)calix[4]resorcinarene, tetra(p-methoxyphenyl)calix[4]resorcinarene, and tetra(p-bromophenyl)calix[4]resorcinarene were synthesized by the cyclocondensation method in acid medium. In the case of tetra(nonyl)calix[4]resorcinarene, only the crown conformer was obtained, while in the case of tetra(p-methoxyphenyl)calix[4]resorcinarene and tetra(p-bromophenyl)calix[4]resorcinarene, a conformational mixture (crown and chair) was formed, separated, and purified via the recrystallization technique. Subsequently, the per-O-acetylation reaction of the pure conformers was carried out. According to the RP-HPLC and 1H-NMR results, the per-acetylation product of the crown conformer of tetra(nonyl)calix[4]resorcinarene retained its conformation, likewise the per-O-acetylation products of the chair conformer of tetra(p-methoxyphenyl)calix[4]resorcinarene and tetra(p-bromophenyl)calix[4]resorcinarene. On the other hand, the per-O-acetylation product of crown conformers of tetra(p-methoxyphenyl)calix[4]resorcinarene and tetra(p-bromophenyl)calix[4]resorcinarene gave rise to the formation of the boat conformer.