Bottom‐Up Approach for the Synthesis of Contorted Nanographenes by Cp*Co(III)‐Catalyzed Annulative‐π‐Extension‐Cyclization Cascade

In the domain of bottom-up approach, regioselective fusion of aromatic moiety onto an arene templet remains scarcely explored, yet represents a crucial tool for the rapid generation of polycyclic aromatic hydrocarbons (PAHs). An unprecedented bottom-up strategy for the rapid construction of PAHs is developed by employing arene-derived ketones and carbon-rich 1,3-diynes. Many of these synthesized PAHs have tilted π-electronic structure, unique edges and topologies. A range of arene-derived ketones participated in this annulative-π-extension-cyclization cascade under first-row Co(III)-catalysis. Electronic nature of the 1,3-diynes guided the final mode of cyclization leading to the formal fusing of one fluorene moiety via 5-exo-dig cyclization or phenanthrene nucleus through 6-endo-dig cyclization. Intermediate ethynyl-PAHs were also isolated in case of relatively electron-deficient diynes. The contorted π-planes of the synthesized PAHs were elucidated by single-crystal X-ray analysis. Detailed DFT studies reinforce the proposed mechanistic pathway, validating the formation of the major regioisomer of PAHs. Furthermore, less aromatic character of fluorene moiety over phenanthrene nucleus is supported by the NICS(1)_zz and ACID calculations.