[2.0.2.0]metacyclophane-1,15-diynes. A potential fragment of double-helical conjugated systems

The title cyclophanes as a potential fragment of double-helical pi-conjugated system were synthesized, and the spectroscopic and crystallographic characterization shows the strained nature of the pi-system; variable-temperature NMR spectra also reveal that the cyclophanes exist as an equilibrium mixture between the meso- and dl-forms in solution.