Unexpected high temperature behaviour of 2,2′-diethynylbiphenyl in the gas phase - A precursor for acephenanthrylene instead of pyrene

Article abstract of DOI:10.1002/jlac.199719971212

Flash Vacuum Thermolysis (FVT) of 2,2′-diethynylbiphenyl (6) gave, instead of pyrene (5), acephenanthrylene (10) and fluoranthene (11) as major products. The unequivocal identification of 9-ethynylphenanthrene (12) at T ≤ 800°C suggests that 12 is the initial stable product derived from 6. It is documented that under high-temperature conditions in the gas phase compound 12 is efficiently converted into 10, which subsequently rearranges to 11. The formation of 12 from 6 is rationalized by invoking the transient formation of cyclobuta[l]phenanthrene (13) by intramolecular cyclization of the ethynyl moieties of 6 followed by a reiro-carbene C-H insertion and a 1,2-H shift. This interpretation is supported by the results of independent FVT of 2,2′-bis(1-chloroethenyl)biphenyl (15). Wiley-VCH Verlag GmbH, 1997.