Triptycene-Cored Double [5]Helicene: Chirality Transfer via the R/S Triptycene Core to P/M Helical Motifs.

A series of double [5]helicenes with a triptycene core were synthesized via photocyclization. Single-crystal X-ray analysis unambiguously confirms these helicenes with an R/S triptycene core and two M/P [5]helicene subunits. Transfer of the central axially helical chirality was observed from R/S-tripytycene as reflected in the diastereoselective, photochemical formation of M/P-[5]helicene. The isolated enantiomers showed persistent chiroptical properties, as inferred from the circular dichroism measurements. Density functional theory calculations suggest that chiral triptycene plays an important role in determining the overall helicity of the system.