Novel Ene Trimerization of 1-Phenylcyclopropene

1-Phenylcyclopropene (1) was synthesized by
treatment of 1,1,2-tribromo-2-phenylcyclopropane (2) with
2.5 equiv of methyllithium followed by protonation. Compound 1 underwent ene dimerization to form ene dimer 5
followed by ene reaction with monomer 1 (enophile) to give
an ene trimer 6. Both of these two ene reactions derived endo
transition states. In the meantime, the [2+2] adduct, trans-1,2-diphenylbicyclo[3.1.0.02,4]hexane (7), was also formed.
When the adduct 7 was heated at THF refluxing temperature, 1,2-diphenylcyclohexa-1,4-diene (8) was obtained. Compound 8 was treated with DDQ to yield o-diphenylbenzene.