Stereoselective Syntheses, Structures, and Properties of Extremely Distorted Chiral Nanographenes Embedding Hextuple Helicenes

We report a molecular design and concept using π‐system elongation and steric effects from helicenes surrounding a triphenylene core toward stable chiral polycyclic aromatic hydrocarbons (PAHs) with a maximal π‐distortion to tackle their aromaticity, supramolecular and molecular properties. The selective syntheses, and the structural, conformational and chiroptical properties of two diastereomeric large multi‐helicenes of formula C90H48 having a triphenylene core and embedding three [5]helicene units on their inner edges and three [7]helicene units at their periphery are reported based on diastereoselective and, when applicable, enantiospecific Yamamoto‐type cyclotrimerizations of racemic or enantiopure 9,10‐dibromo[7]helicene. Both molecules have an extremely distorted triphenylene core, and one of them exhibits the largest torsion angle recorded so far for a benzene ring (twist=36.9°). A twist to dearomatize benzene: The stereoselective and/or stereospecific syntheses and thorough analyses of two diastereomeric hextuple helicenes of formula C90H48 are described. One of these fascinating molecules embeds an extremely distorted benzene ring (red colored in the picture) with a torsion angle of 36.9° and a non‐aromatic character.