A novel tandem Ru-catalyzed [2+2+2] cycloaddition of arylenynes
to dihydrobiphenylenes followed by halogen-radical ring opening has
been developed for the construction of tub-shaped halogenated benzocyclooctatetraenes
(bCOT’s). Cross-couplings and Diels–Alder reactions
of the brominated bCOT’s allow the formation of the corresponding
eight-membered ring-fused PAH’s. The halogen-radical ring opening
probably occurs via a selective formation of a bis-allyl radical at
the 1,3-cyclohexadiene moiety, halogenation at the bridgehead carbon,
and finally electrocyclic ring opening.
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