Planar Chirality Controls Diastereotopicity in [2.2]Paracyclophanyl Cyclopropenes

The synthesis of [2.2]paracyclophanyl (pCp) cyclopropenes through rhodium-catalyzed [2+1] cycloaddition of alkynes with a pCp-derived carbene is reported. The [2.2]paracyclophane topology induces diastereotopic differentiation of the alkyl substituents in the resulting cyclopropenes, which is consistently observed in their 1H NMR spectra. Oxidation to the corresponding cyclopropenium ions removes this stereochemical bias and restores substituent equivalence, reflecting an increase in symmetry upon aromatization.