Dimerization of 9-Phenylethynylfluorene to Di-indeno-naphthacene and Dispiro-[fluorene-dihydronaphthacene- fluorene]: An X-ray Crystallographic and NMR Study

The attempted Diels−Alder reaction between 9-phenylethynylfluorene and tetracyclone yields instead three products resulting from the dimerization
of the isomeric allene. The major product is 8,16-diphenyl-diindeno[1,2,3-de:1‘,2‘,3‘-mn]naphthacene, in which each terminal ring is derived
from a fluorenyl unit; aerial oxidation then yields a peroxide. A dihydronaphthacene bearing fluorenyl moieties spiro-bonded at the C(5) and
C(11) positions was also identified. The structures of the naphthacenes were elucidated by X-ray crystallography, and a mechanistic rationale
is offered.