Twofold π-Extension of Polyarenes via Double and Triple Radical Alkyne <i>peri</i> -Annulations: Radical Cascades Converging on the Same Aromatic Core

Abstract

A versatile synthetic route to distannyl-substituted polyarenes was developed via double radical <i>peri</i>-annulations. The cyclization precursors were equipped with propargylic OMe traceless directing groups (TDGs) for regioselective Sn-radical attack at the triple bonds. The two <i>peri</i>-annulations converge at a variety of polycyclic cores to yield expanded difunctionalized polycyclic aromatic hydrocarbons (PAHs). This approach can be extended to <i>triple</i> <i>peri</i>-annulations, where annulations are coupled with a radical cascade that connects <i>two</i> preexisting aromatic cores via a formal C-H activation step. The installed Bu₃Sn groups serve as chemical handles for further functionalization via direct cross-coupling, iodination, or protodestannylation and increase solubility of the products in organic solvents. Photophysical studies reveal that the Bu₃Sn-substituted PAHs are moderately fluorescent, and their protodestannylation results in an up to 10-fold fluorescence quantum yield enhancement. DFT calculations identified the most likely possible mechanism of this complex chemical transformation involving two independent <i>peri</i>-cyclizations at the central core.