Aromatic Architecture Based on cis Conformational Preference of N-Methylated Amides

摘要

Aromatic secondary amides such as benzanilide (1) exist in trans-amide form both in the crystal and in solution, whereas N-methylbenzanilide (2) exists in cis form in the crystal, and predominantly in cis form in various solutions. Similar cis conformational preferences were observed in the aromatic N,N'-dimethylated urea (4) and guanidine (7), in which two aromatic rings are located face-to-face. The cis conformations of N-methylated amides, ureas and guanidines could be utilized to construct interesting aromatic architecture. First, N,N',N''-trimethyl-N,N',N''-triphenyl-1,3,5-benzenetricarboxa-mide (12) and a cyclic triamide 14 have crsytal structures in which three N-phenyl groups exist with the same orientation (syn conformation). Second, several aromatic amides which have no fixed asymmetric center afforded chiral crystals by simple recrystallization. I the case of 1,2-bis(N-benzoyl-N-methylamino)benzene (18), two enantiomeric crystals could be distinguished morphologically or on the basis of symmetrical CD spectra in KBr, and by ~1H-NMR in the presence of chiral 1,1'-bi-2-naphthol. Third, aromatic multi-layered structures could be constructured by using N,N'-dimethylated urea or guanidino bonds. These unique layered structures could be applied to obtain aromatic molecules with potent DNA-binding ability.