Post-Modification of Tripyrenylenes to Enantiopure π-Extended D3-Symmetric Propellers.

A palladium-catalyzed trimerization of a pyrene-based Kobayashi aryne precursor and post-functionalization of the obtained tripyrenylene was used to synthesize polycyclic aromatic hydrocarbons with multiple helicene subunits. The isomerization of the obtained C2-isomers to the corresponding propeller-shaped D3-isomers was investigated and the enantiomers of a D3-pyrenylene as well as a D3-trisphenanthrophenazine were isolated. Their chiroptical properties as well as the crystalline packings in comparison to the corresponding racemates were studied and the isomerization as well as racemization processes were investigated kinetically and by quantum chemical calculations.