The Crossed [2+2] Cycloaddition of 1-Phenylcyclopropene and 1-Bromo-2-phenylcyclopropene

1-Bromo-2-phenylcyclopropene (2) underwent [2+2] dimerization to generate 1,2-dibromo-4,5-diphenyltricyclo[3.1.0.02,4]hexane (5), which was heated to form 1,2-dibromo-4,5-diphenylcyclohexa-1,4-diene (6) followed by oxidation to yield 4′,5′-dibromo-o-terphenyl (7). o-Terphenyl 7 could be synthesized in one-pot reactions from 1,1,2-tribromocyclopropane (3). When cyclopropane 3 was treated with 1.5 equiv of methyllithium followed by slowly adding the proton source, crossed [2+2] adduct 8 was isolated in 40% yield. Compound 8 was heated and oxidated to produce 4′-bromo-o-terphenyl (11).