Synthesis and Stereochemical Properties of Chiral Hetero[7]helicenes Structured by a Benzodiheterole Ring Core

A new hetero[7]helicene 1NN structured by a diaza-benzodiheterole (pyrroloindole) ring core was successfully synthesized by catalytic domino cyclodehydrogenation with Pd(OAc)2 and O2 as the key step. Significantly, 1NN was stereochemically stable at room temperature and could be subjected to optical resolution by chiral HPLC. Furthermore, kinetic analysis of 1NN and DFT calculations on its variants revealed that the stereochemical stability of the benzodiheterole-based helicenes was highly dependent on not only the heteroaromatic ring component but also the N-substituent of the pyrrole ring unit.