A Chiral Adamantanophane: Preparation, Enantiomer Separation, Theoretical and Experimental Circular Dichroism and Absolute Configuration

Exchange of aromatic units (e.g. benzene) for ali phatic/ ali ‐cyclic building blocks (e.g. adamantane) in cyclophanes leads to molecules of the “ araliphane ” type. The synthesis of the highly strained [2.2](1,3)adamantanometacyclophanes 5a–c is described. The cyclophane skeletons of these molecules are conformationally rigid and therefore 5a–c are planar‐chiral. The circular dichroism of 5c has been calculated theoretically with NDDO/MRD‐CI methods and was measured. Agreement of theory and experiment is good, a comparison of both allows the assignment of the absolute configuration of the two enantiomers of 5c with high probability. Furthermore, analysis of the nπ * band in the CD spectrum yields a, simple general rule to determine the conformation of the carboxyl group in phenyl ester substructures. Theoretical calculations of the strain energy ( E s ) of 5c reveal the distribution of strain within the molecule.