exo-10,11-Dibromo-tricyclo-[6.3.1.0]dodeca-2,4,6,9-tetra-ene

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 inexopositions. 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 C2H4bridge 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. Thiscis-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)°].