Heating 1,2-bis(phenylethynyl) benzene in the presence of 1,4-cyclohexadiene at temperatures ranging from 260 to 360°C yielded the expected 2,3-diphenylnaphthalene, as only a minor product (<3%) under all reaction conditions studied. The major products, resulting from one or more phenyl shifts, were 1,3- and 1,4-diphenylnaphthalene which formed in up to 16% and 11% yield, respectively. Although somewhat less efficiently, 1-ethynyl-2-(phenylethynyl)benzene and (Z)-1,6-diphenylhex-3-ene-1,5-diyne also yielded products resulting from phenyl shifts. These results are explained through computations that point to the role of steric repulsion and benzene diradical stability in driving these isomerizations. The computed barriers for phenyl shifting are dramatically higher than those observed in the case of sp³ radicals. However, these transformations are relevant in solution chemistry as well as in more extreme environments such as pyrolysis, and electric discharge heating.

1,2-bis(phenylethynyl)benzene を1,4-cyclohexadieneの存在下、260〜360°Cで加熱すると、実験を行った全ての条件において予想した2,3-diphenylnaphthaleneが副生成物（<3%）としてのみ生成した。主生成物は1つ、もしくはそれ以上のphenyl shiftが起こった1,3-と1,4-diphenylnaphthaleneが生成した（16%, 11%）。いくらか効率は低いが、1-ethynyl-2-(phenylethynyl)benzeneと(Z)-1,6-diphenylhex-3-ene-1,5-diyneもまたphenyl shiftが原因である化合物を生成した。これらの結果は、異性化を駆動力にし、立体反発とベンゼンジラジカルの安定性を示す計算で説明される。計算で求められたphenyl shiftの障壁は、sp³ラジカルの場合に観測された障壁よりも相当高い。しかしこれらの変換は、溶液中での化学だけではなく、さらに厳しい条件である熱放電やFVPにも関連がある。

Kevin D. Lewis and Adam J. Matzger* J. Am. Chem. Soc., 127 (28), 9968