Helical Folding of <i>Meta</i>-Connected Aromatic Oligoureas

Aromatic oligoureas composed of meta-linked residues bearing phenolic ether side chains are synthesized. The basic N,N′-diarylurea units adopt a trans,trans intramolecularly H-bonded conformation that is further strengthened by additional intermolecular H-bonding. Such basic units, in combination with meta-linked benzene residues, result in stably folded helical oligoureas in the highly polar DMF with up to four turns and with a small cylindrical inner pore that would be difficult to acquire.