Synthesis and conformational analysis of extended calix[4]arenes and a doubly bridged bis-calix[4]arene

Abstract

Calix[4]arenes extended at the 5 and 17 upper rim positions with arylamide substituents have been prepared via a tetrapropoxycalixarene-5,17-dicarboxylic acid. Also, a surprisingly facile cyclooligomerization leading to the dimeric and tetrameric calix[4]arenes 1 and 2 with arylamide bridges has been developed. NMR investigations including NOE difference measurements showed that N,N′-bis(4-nitrophenyl)tetrapropoxycalix[4]arene-5,17-dicarboxamide 5 exists in two different pinched cone conformations: 5a in [²H₆]-DMSO and 5b in CDCl₃. With this background, the conformation of the dimer 1 could be inferred. Finally, binding studies with 1 and 5 as hosts and benzene, naphthalene, anthracene and pyrene as guests have been investigated and related to the solvent-dependent conformations.