Synthesis and Inclusion Properties of a Upper-rim-connected Biscalix[4]arene

The conformationally-immobile biscalix[4]arene was synthesized by connecting the upper rims with two spacers. It showed high inclusion ability and selectivity for quaternary ammonium ions. A comparison with reference compounds established that the enhanced selectivity is due to the cooperative action of two bowl-shaped calix[4]arenes.