Planar Chiral Dianthranilide and Dithiodianthranilide Molecules: Optical Resolution, Chiroptical Spectra, and Molecular Self-Assembly
2004-02-20T00:00:00Z (GMT) by
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.