Helical Molecular Cages with sp-Conjugated Linkages

A conjugated helical cage, comprising two 1,3,5-tris(phenylethynyl)benzene units connected by diyne linkers, was successfully synthesized. X-ray crystallography revealed helical molecular structures with large twisted angles and a 1:1 mixture of P- and M-enantiomers. Variable-temperature-NMR measurement indicated the racemization process between the enantiomers occurs rapidly on the NMR timescale. The rapid interconversion is attributed to the flexible diyne linkages, even though they were believed to be rigid.