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.