Unusually rigid macrocyclic tris(picolinolato)-4-tert-butylcalix[4]arene: Its intramolecular interaction effect on picolinoylation

The reaction of 4-tert-butylcalix[4]arene (calix[4]) with picolinoyl chloride affords only the unprecedented rigid tris(pico)-product calix[4]-(pico)3(OH) (pico = picolinoylato) with an upper-rim and two lower-rim pico groups, via a subtle combination of steric hindrance and intrinsically weak intramolecular interactions. The chemical shift of one of the upper-rim pico group’s aromatic protons appears, unusually, 5.18 ppm in chloroform, which is the quite up-field chemical shift of the reported aromatic proton signals.