4,4-diphenylcyclohexa-2,5-dienylidene: Rearrangement via an isobenzene pathway

Pyrolytic decompostition of the Li salt of the tosylhydrazone of 4,4-diphenyl-2,5-cyclohexadienone produces a mixture of products which includes biphenyl, p-terphenyl, the azine of 4,4-diphenyl-2,5-cyclohexadienone, and o-terphenyl. C-13 labeling studies and computational results (semiempirical AM1 and density functional B3LYP/6-31G* molecular orbital calculations) elucidate the mechanistic pathway for the formation of o-terphenyl. A single mechanism is involved which proceeds through formation of an isobenzene species followed by subsequent phenyl and hydrogen migrations.