Rhodium-Catalyzed Intermolecular Arylative [2 + 2 + 1] Annulation-Oxidation to Produce Electron-Deficient Azulene-Embedded Polycyclic Aromatic Hydrocarbons.

Azulene derivatives have attracted much attention for their application in organic electronic materials and devices because of their large dipole moment and small HOMO-LUMO energy gap. As these physical properties of azulene depend on its substitution and condensation patterns, developing methods to synthesize functionalized and π-extended azulenes is desirable. However, synthesizing π-extended azulenes requires harsh reaction conditions, making it hard to achieve both functionalization and π-extension. Here, we report the synthesis of electron-deficient azulene-embedded polycyclic aromatic hydrocarbons (PAHs) with two alkoxycarbonyl groups by the rhodium-catalyzed intermolecular arylative [2 + 2 + 1] annulation of teraryl diynes with dialkyl acetylenedicarboxylates followed by oxidation at room temperature. Interestingly, for the electron-rich diyne, prolonged oxidation time after the arylative [2 + 2 + 1] annulation yields a helicene-like bis(azulene-embedded PAH) in good yield. Thus, obtained electron-deficient fused azulenes have small HOMO-LUMO energy gaps (up to E  = 1.52 and E  = 2.06), resulting in long-wavelength absorption extending into the near-infrared region. Due to bulky electron-withdrawing groups and π-extension, the molecule becomes saddle-shaped and highly polarized, and strong π-π stacking interactions are observed in both the solid and solution states.