Tetrabromobutatriene: Completing the Perhalocumulene Series

Tetrabromobutatriene, C4Br4, can be prepared directly from dibromobutadiyne by reaction with Br2 at −25 °C in concentrated hexanes solution.
The cumulene precipitates out of the reaction mixture as a yellow powder. Under palladium-catalyzed coupling conditions, C4Br4 can undergo
allylic rearrangement, giving a mixture of products, including some with butenyne backbones. However, in furan solution, C4Br4 reacts cleanly
at its central double bond to give the furan Diels−Alder adduct. Under Suzuki conditions, this adduct reacts at the furan double bond rather
than at bromide.