A tetra­bromo-1,4-ethano­naphthalene and related dibromo-1,4-etheno­naphthalene

(1RS,3RS,4RS,10SR)-2,2,3,10-Tetra­bromo-1,2,3,4-tetra­hydro-1,4-ethano­naphthalene, C₁₂H₁₀Br₄, (I), is the first structure to be reported with four Br atoms bound to a 1,4-ethano­naphthalene framework and also the first which possesses three Br atoms in exo positions. Inter­actions between the Br atoms [three short intra­molecular Br...Br distances of 3.1094 (4), 3.2669 (4) and 3.4415 (5) Å] have little effect on the C—C bond lengths but lead to significant twisting of the cage structure compared with the parent hydro­carbon, which is expected to be fully eclipsed at the two saturated C₂H₄ bridge positions. Chemically related (1SR,4RS)-2,3-dibromo-1,4-etheno­naphthalene, C₁₂H₈Br₂, (II), obtained by double dehydro­bromination of (I), represents the first structure of any halogen-substituted benzobarrelene. This cis-dibromide shows little evidence of steric congestion at the double bond [Br...Br = 3.5276 (8) Å] as a consequence of the large C—C—Br angles [average C=C—Br angle = 126.15 (10)°].