Stereoselective Nanocarbon Imides Featuring 12-fold [5]helicenes

Despite the great progress in research on chiral molecular nanocarbons containing multiple helicenes, controlling the stereoselectivity is still a major challenge, especially when attempting to increase the number of helicene moieties. Herein, a novel molecular nanocarbon imides composed of C204 skeleton and eighteen imide groups was successfully synthesized via an inside–out ring closing strategy involving repeated Suzuki–Miyaura coupling for C–C bond formation and photocyclic aromatization. Because of the presence of quad–core twelvefold [5]helicenes, there are, in theory, more than one hundred stereoisomers. However, only one pair of stereoisomers with D3 symmetry was observed. Despite the large and rigid skeleton, the (3M,3M,3M,3M)+(3P,3P,3P,3P) enantiomers were successfully separated by chiral HPLC, and the chiroptical properties were investigated by CD spectroscopy.