Cope Rearrangement versus a Novel Tandem Retro-Diels−Alder−Diels−Alder Reaction with Role Reversal^†

A reinvestigation of the thermolysis of 4,4-dibromotetracyclo[6.2.1.0^2,7.0^3,5]undec-9-ene (2) affords diene 8 with a completely rearranged hydrocarbon skeleton via the isolable intermediate 4, along with cyclopentadiene and bromobenzene. DFT calculations show that the novel tandem retro-Diels−Alder−Diels−Alder reaction with role reversal is slightly less favored than the overall single-step Cope rearrangement.