L-region-selective annulative π-extension through dearomative activation of polycyclic aromatic hydrocarbons

Annulative π-extension (APEX) reaction is a useful aromatic ring-fusion method for the synthesis of large polycyclic aromatic hydrocarbons (PAHs) from unfunctionalized small PAHs. While APEX reactions in the K-, M-, and bay-regions of PAHs have been developed, L-region selective APEX is yet to be achieved. Herein, we report a stepwise L-region selective APEX of unfunctionalized PAHs by dearomative activation with N-methyltriazoline dione, followed by Pd-catalyzed annulation with aryl Grignard reagents. Various difficult-to-synthesize core-expanded PAHs can be synthesized by L-APEX from unfunctionalized naphthalene, phenanthrene, chrysene, and [4]helicene.