Fluorinated Phenanthrenes as Aryne Precursors: PAH Synthesis Based on Domino Ring Assembly Using 1,1‐Difluoroallenes

Abstract

On treatment with the catalyst InBr₃, 1,1‐difluoroallenes that bear a cyclopentene moiety and an aryl group underwent domino ring assembly in the presence or absence of N‐bromosuccinimide or N‐iodosuccinimide to afford aryne precursors such as three‐ringed ortho‐fluoro(halo)phenanthrenes, four‐ringed ortho‐fluoro(halo)tetraphenes, ortho‐fluoro(halo)chrysenes and fluoro[4]helicenes. Metalation of the aryne precursors followed by elimination of the fluoride resulted in the unprecedented systematic generation of arynes bearing π‐extended systems. Diels−Alder reactions of these arynes with isobenzofurans afforded the corresponding cycloadducts whose reductive aromatisation in an SnCl₂/HBr system furnished fully aromatised benzotriphenylenes. In addition, oxidative aryl−aryl coupling (the Scholl reaction) of these benzotriphenylenes facilitated the synthesis of ‘half HBCs’ (hexabenzocoronenes).