Enantioselective synthesis of a two-fold inherently chiral molecular nanographene

Abstract

The introduction and precise control of stereogenic elements in chemical structures is typically a challenging task. Most asymmetric methods require the presence of a heteroatom in the starting substrates acting as an anchor point for the successful transfer of chiral information. For this reason, compounds comprising only carbon atoms, such as optically active molecular nanographenes, are usually obtained as racemates, and isolated by chiral chromatographic separation. Here, we report an enantioselective strategy that uses three stereocontrolled synthetic steps to introduce and extend three different types of stereogenic elements, namely central, axial and helicoidal chirality, into a polycyclic aromatic structure. Thus, two chiral nanographene layers are covalently connected through a chiral triindane core. The final stereocontrolled graphitization Scholl reaction affords the formation of chiral nanographene units with remarkable enantiomeric excesses, high stereochemical stability and good chiroptical properties.