Synthesis of soluble aromatic multilayered tetra(m-phenylurea) and analysis of its helical conformation in various solvents.

Aromatic N,N'-dimethylated urea exists in (cis, cis) form, both in the crystal and in solution, and this structure can be utilized to construct intramolecular aromatic multilayered oligomers. These structures show helical conformation with all-R or all-S axis chirality, when the benzene rings are connected at the meta positions. To investigate the dynamic conformational behavior of such aromatic multilayered ureas in various solvents, we synthesized tetra(m-phenylurea) 3 bearing two chiral N-2-(methoxyethoxyethoxy)propyl groups and six N-methoxyethoxyethyl groups. The high solubility of compound 3 enabled its analysis in various solvents, including water. The CD spectra of compound 3 showed broad electronic absorption with high temperature-dependency, owing to the induction of handedness, in acetonitrile, chloroform, and methanol. In water, the CD signals of compound 3 indicated the presence of similar helical structure, but temperature-dependency was not observed.