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

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).