Synthesis of a Bent, Twisted, and Chiral Phenanthrene via an Iodine Monochloride-Mediated, Strain-Inducing π-Extension Reaction

Controlling helicene's pitch by molecular tethering

We applied post-cyclization annulation to introduce a series of tethered S-shaped double [4]helicenes in which the intramolecular tether imposes a specific helical handedness. Introducing a tether and then shortening the tether length incrementally increase the pitch angle of [4]helicene, thus enabling a quantitative study of the effects of helicene's pitch on its electronic and (chiro)optical properties.

Gold-Catalyzed 1,2-Aryl Shift and Double Alkyne Benzannulation

The tandem intramolecular hydroarylation of alkynes accompanied by a 1,2-aryl shift is described. Harnessing the unique electron-rich character of 1,4-dihydropyrrolo[3,2-b]pyrrole scaffold, we demonstrate that the hydroarylation of alkynes proceeds at the already occupied positions 2 and 5 leading to a 1,2-aryl shift. Remarkably, the reaction proceeds only in the presence of cationic gold catalyst, and it leads to heretofore unknown π-expanded, centrosymmetric pyrrolo[3,2-b]pyrroles. The utility is verified in the preparation of 13 products that bear six conjugated rings. The observed compatibility with various functional groups allows for increased tunability with regard to the photophysical properties as well as providing sites for further functionalization. Computational studies of the reaction mechanism revealed that the formation of the six-membered rings accompanied with a 1,2-aryl shift is both kinetically and thermodynamically favourable over plausible formation of products containing 7-membered rings. Steady-state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S-shaped N-doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. Their optical properties are rationalized through time-dependent density functional theory calculations. We anticipate that this chemistry will empower the creation of new materials with various functionalities.