Enantioselective Synthesis of Inherently Chiral Molecular Nanographenes

Abstract

Abstract The introduction and precise control of stereogenic elements in chemical structures is always a challenging and highly demanding task. The vast majority of available asymmetric methods require the presence of a heteroatom in the starting substrates acting as an anchor point for the successful transfer of chiral information. This eventually emerges, typically, in the formation of a new stereogenic centre while the heteroatom remains in the product. For this reason, compounds constituted only by carbon atoms, such as optically active molecular nanographenes have, so far, been obtained as racemates followed by chiral chromatographic separations. Here, we report an enantioselective strategy which uses three pivotal stereocontrolled key synthetic steps to introduce and extend three different types of stereogenic elements, namely central, axial and helicoidal chirality, into a polycyclic aromatic Csp2-based structure. The resulting helicity of six ortho-fused rings embedded in the triindane-based nanographene ensures stereochemical stability and good chiroptic activity.