Chiral Organic Cages with a Triple-Stranded Helical Structure Derived from Helicene

We
report the use of helicene with an intrinsic helical molecular
structure to prepare covalent organic cages via imine condensation.
The organic cages revealed a [3+2]-type architecture containing a
triple-stranded helical structure with three helicene units arranged
in a propeller-like fashion with the framework integrally twisted.
Such structural chirality was retained upon dissolution in organic
solvents, as indicated by a strong diastereotopy effect in proton
NMR and unique Cotton effects in circular dichroism spectra. Further
study on chiral adsorption showed that the chiral organic cages possess
considerable enantio­selectivity toward a series of aromatic
racemates.