The synthesis of C2-sym. [6]cycloparaphenylene (CPP) tetracarboxylates has been achieved via macrocyclization by the rhodium-catalyzed intermol. stepwise cross-alkyne cyclotrimerization and subsequent reductive aromatization. The 1H NMR spectra of the thus-obtained C2-sym. [6]CPP-tetracarboxylates revealed that the rotation of unsubstituted benzene rings is slow at room temp. These [6]CPPs formed columnar packing structures, and their absorption maxima were significantly blue-shifted compared to that of nonsubstituted [6]CPP due to the presence of four electron-withdrawing ester moieties. [on SciFinder(R)]
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