Synthesis of Belt- and Mobius-Shaped Cycloparaphenylenes by Rhodium-Catalyzed Alkyne Cyclotrimerization

A belt-shaped [8] cycloparaphenylene (CPP) and an enantioenriched Mobius-shaped [10]CPP have been synthesized by high-yielding rhodium-catalyzed intramolecular cyclotrimerizations of a cyclic dodecayne and a pentadecayne, respectively. This Mobius-shaped [10]CPP possesses stable chirality and isolated with high enantiomeric purity. It is evident from the reaction Gibbs energy calculation that the above irreversible cyclotrimerizations are highly exothermic; therefore establishing that the intramolecular alkyne cyclotrimerization is a powerful route to strained cyclic molecular strips.