Synthesis and properties of calixarene analogs incorporating a thiophene unit in the macrocyclic ring

Calixarene analogs containing a thiophene unit in the macrocyclic ring were prepared by a stepwise method. The macrocycles adopt a cone-like form as the preferred conformation in solution. The induced chemical shift change, nOe experiment, and 1H relaxation time (T1) measurement supported the fact that the macrocycle forms a complex with the N-methylpyridinium salt. In contrast, O-tetramethylated macrocycles and linear phenol-formaldehyde tetramer, could not efficiently include the N-methylpyridinium salt.