Discovery of cis-preference of aromatic N-methylamides and its application to molecular constructions

Abstract

Aromatic secondary amides such as benzanilide (1) exist in a trans-amide form both in the crystal and in the solution, whereas N-methylbenzanilide (2) exists in cis form in the crystal, and predominantly in a cis form in the solution. Similar cis conformational preferences were observed in aromatic N,N'-dimethylated ureas and guanidines, in which two aromatic rings are located face to face. The cis preferences of N-methylated amides, ureas and guanidines could be utilized to construct interesting aromatic architecture. N,N',N"-Trimethyl-N,N',N"-triphenyl-1,3,5-benzenetricarboxamide (20) and a cyclic triamide (24) have crystal structures in which three N-phenyl groups direct to the same orientation (syn conformation). 1,2-Bis(N-benzoyl-N-methylamino)benzene (22), which have no fixed asymmetric center, afforded chiral crystals by simple recrystallization. Furthermore, aromatic multi-layered structures could be built and applied to obtain aromatic molecules which have potent DNA-binding ability.