Molecular self-assembly and optical activity of chiral thionooxalamic acid esters

Abstract

Three chiral bisthionooxalamides were synthesized by acylation with ethyl or (1 R)-menthyl chloroxoacetate of the corresponding diamines and subsequent thionation with Lawesson’s reagent. Single crystal X-ray diffraction analysis revealed that products 4b– 7b self-assemble in the solid state by the ring [N–H⋯O C, R 2 2 ( 10 ) ] or chain [N–H⋯S C, C(4)] hydrogen-bond motifs. Only in the case of 4b was a helical superstructure formed. In racemic compound 6b, the molecules are connected via N–H⋯S C hydrogen bonds into homochiral chains, similar to those formed in 7b. The solid state CD spectra of chiral bisthionooxalamides are characterized by strong Cotton effects in the region of the thioamide n–π ∗ transition. Their sign is determined by the helicity of the S C–C O unit.