Chiroptical Signatures of Planar and Central Chirality in [2]Paracyclo[2](5,8)quinolinophane Derivatives

Electronic and vibrational circular dichroism (ECD and VCD) spectra and specific optical rotation measurements at the sodium D-line (OR) have been taken for thirteen chiral [2]paracyclo[2](5,8)quinolinophane derivatives and calculated by density functional theory. Besides the planar chirality from the paracyclophane moiety in all molecules, some of the investigated compounds also exhibit central chirality due to an asymmetric carbon atom in the side-chain bound at C-2 of the heterocyclic ring. Characteristic bands for each type of chirality were clearly identified in the VCD spectra in the CH-stretching and mid-IR regions, allowing assignment of absolute and relative configurations. ECD was found to be sensitive mostly, if not exclusively, to planar chirality, whereas OR was also very sensitive to central chirality. Configurational assignment of the different diastereomers by the present method provided results that are in agreement with those inferred from NOE-NMR experiments.