Synthesis of Unsymmetrically Substituted [5]Helicenes by Tandem Arylation of Binaphthyl by Suzuki Coupling and C−H Activation

Abstract

We report a step‐efficient approach for the synthesis of unsymmetrically substituted naphtho[1,2‐g]chrysenes by tandem arylation of 2,2’‐diiodo‐1,1’‐binaphthyl with arylboronic acids, which proceeds through Suzuki coupling followed by intramolecular arylation by C−H activation. Substrate screening examining over 30 meta‐ and/or para‐substituted arylboronic acids showed that this approach provides the desired helicene products most effectively if arylboronic acids have a small acidifying group at the meta‐position. In the case of unsymmetrically substituted arylboronic acids, the regioselectivity of C−H activation is directed by the attached group(s), its effect on the C−H acidity of the adjacent position, its coordination ability, as well as steric hindrance. Interestingly, selected [5]helicenes exhibited attractive deep blue emission with fluorescence lifetimes slightly exceeding 10 ns.