Synthesis of [8]Cycloparaphenylene-octacarboxylates via Rh-Catalyzed Stepwise Cross-Alkyne Cyclotrimerization

The synthesis of C₄- and C₂-symmetrical [8]cycloparaphenylene (CPP)-octacarboxylates has been achieved via macrocyclization by the rhodium-catalyzed intermolecular stepwise cross-cyclotrimerization and subsequent reductive aromatization. The C₄-symmetrical octa-tert-butyl [8]CPP-octacarboxylate forms a dimer in which eight ester moieties face each other. The dimers are aligned so as to make a one-dimensional column with a channel structure inside. Both absorption and fluorescence maxima of [8]CPP-octacarboxylates in CHCl₃ were significantly blue-shifted compared to those of [8]CPP due to the presence of eight electron-withdrawing ester moieties.