No abstract

Helical hexabenzo[4.4.4]propellane (a relative of hexaphenylethane) and its derivatives are synthesized and their structures are established by X-ray crystallography. Isolation and X-ray crystallographic characterization of a robust trication-radical salt of hexamethoxypropellane derivative confirms that its framework is stable toward oxidative (aliphatic) C-C bond cleavage. It is also demonstrated that propellane can be easily brominated at the 4,4'-positions of the biphenyl linkages for its usage as a molecular platform for the preparation of electroactive materials.

A versatile synthesis of a new class of polyaromatic receptors (stilbenoprismands) containing a Delta-shaped cavity similar to that of the pi-prismand together with an intimately coupled electroactive stilbenoid moiety was accomplished via an efficient intramolecular McMurry coupling reaction. The presence of the Delta-shaped cavity in stilbenoprismands allows an efficient binding of a single silver cation as probed by (1)H NMR spectroscopy. Electron-rich stilbenoprismands undergo a ready oxidation to their highly robust cation-radical and dicationic salts. X-ray structure determination of a representative dicationic stilbenoprismand showed that the charges were largely localized on the tetraarylethylene moiety, which results in a twisting of the ethylenic C=C bond by approximately 35 degrees. Moreover, the electronic coupling among the stilbenoid and pi-prismand moieties in various stilbenoprismands was briefly probed by optical methods.

[reaction: see text] Receptor 1 featuring two open arms, multipoint binding sites, and unsaturated linkers on a ferrocene platform shows strong 1:1 binding to unprotected alpha-amino acids (UV-vis, fluorescence, CV, ITC, NMR, and ESI-MS). NMR and ESI-MS studies suggest an encapsulative binding mode involving the alpha,beta-unsaturated carbonyl residue (site for -NH3+, interaction A) and the terminal -OH groups (site for -COO-, interaction B).