Planar Chiral Dianthranilide and Dithiodianthranilide Molecules: Optical Resolution, Chiroptical Spectra, and Molecular Self-Assembly
2004-02-20T00:00:00Z (GMT) by
Planar chiral dianthranilide (<b>1</b>) was resolved to enantiomers with use of (−)-(1<i>S</i>,4<i>R</i>)-camphanoyl chloride as a chiral derivatizing agent. The (+)-<b>1 </b>enantiomer was assigned the <i>S</i> absolute configuration from the X-ray crystal structure of its <i>N</i>,<i>N</i>‘-dicamphanoyl derivative. Optical resolution of dithionodianthranilide (<b>2</b>) was accomplished by inclusion crystallization with (<i>R</i>,<i>R</i>)-1,2-diaminocyclohexane, and the X-ray structure of the corresponding adduct revealed the (−)-<b>2 </b>stereoisomer has the <i>R</i> configuration. A slow boat-to-boat ring inversion (Δ<i>G</i><sup>⧧</sup> = 24.1 ± 0.1 kcal mol<sup>-1</sup>) causes racemization of (+)-<b>1 </b>in solution as manifested by a gradual decrease of the CD spectrum whereas, (−)-<b>2 </b>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 <b>1</b> and <b>2 </b>show different self-assembly patterns: the racemate (±)-<b>1</b> prefers the cyclic R<sub>2</sub><sup>2</sup>(8) hydrogen bond motif, whereas the crystalline DMSO solvates of (±)-<b>1</b> and (+)-<b>1</b> consist of 1D homochiral hydrogen-bonded assemblies generated by the C(6) motif. In the case of dithionolactams (±)-<b>2</b> and (−)-<b>2</b> two types of 1D networks were observed: in the racemate they are generated by the centrosymmetric R<sub>2</sub><sup>2</sup>(8) and R<sub>2</sub><sup>2</sup>(12) hydrogen bond motifs, whereas the molecules in the homochiral crystals are connected solely with use of the strongly nonplanar R<sub>2</sub><sup>2</sup>(8) motif.