Studies in the cyclopropa-arene series: acid-catalysed and thermal decompositions of 1,1-dichloro-2,5-diphenylcyclopropabenzene

1,1-Dichloro-2,5-diphenylcyclopropabenzene (1) readily decomposes in solution in halogenomethanes giving the isomeric tropones (4) and (5), and (E)-2,2′3,3′-tetrachloro-4,4′,7,7′-tetraphenyl-1,1′-bicycloheptatrienylidene (8). On mild thermolysis in solution, compound (1) affords a mixture of two dimers, the 1,1′-bicycloheptatrienylidine (8) and an unidentified isomer.