Planar Chiral Dianthranilide and Dithiodianthranilide Molecules:  Optical Resolution, Chiroptical Spectra, and Molecular Self-Assembly

Planar chiral dianthranilide (1) was resolved to enantiomers with use of (−)-(1S,4R)-camphanoyl chloride as a chiral derivatizing agent. The (+)-1 enantiomer was assigned the S absolute configuration from the X-ray crystal structure of its N,N‘-dicamphanoyl derivative. Optical resolution of dithionodianthranilide (2) was accomplished by inclusion crystallization with (R,R)-1,2-diaminocyclohexane, and the X-ray structure of the corresponding adduct revealed the (−)-2 stereoisomer has the R configuration. A slow boat-to-boat ring inversion (ΔG^⧧ = 24.1 ± 0.1 kcal mol^-1) causes racemization of (+)-1 in solution as manifested by a gradual decrease of the CD spectrum whereas, (−)-2 is configurationally stable at these conditions. The analysis of the CD spectra of the title compounds showed that the n−π* Cotton effect signs are determined by the helicity of the skewed benzamide and thiobenzamide chromophores. The solid-state structures of the racemic and homochiral forms of 1 and 2 show different self-assembly patterns:  the racemate (±)-1 prefers the cyclic R₂²(8) hydrogen bond motif, whereas the crystalline DMSO solvates of (±)-1 and (+)-1 consist of 1D homochiral hydrogen-bonded assemblies generated by the C(6) motif. In the case of dithionolactams (±)-2 and (−)-2 two types of 1D networks were observed:  in the racemate they are generated by the centrosymmetric R₂²(8) and R₂²(12) hydrogen bond motifs, whereas the molecules in the homochiral crystals are connected solely with use of the strongly nonplanar R₂²(8) motif.