Tetrabromo-o-xylene

α,α,α',α'-Tetrabromo-o-xylene is an organobromine compound with the formula C6H4(CHBr2)2. Three isomers of α,α,α',α'-Tetrabromoxylene exist, but the ortho derivative is most widely studied. It is an off-white solid. The compound is prepared by the photochemical reaction of o-xylene with elemental bromine:
 * C6H4(CH3)2 + 4 Br2 → C6H4(CHBr2)2 + 4 HBr

Reaction of α,α,α',α'-tetrabromo-o-xylene with sodium iodide affords α,α'-dibromo-o-xylylene, which can be trapped with dienophiles to give naphthylene. In the absence of trapping agents, the xylylene relaxes to α,α'-dibromobenzocyclobutane:
 * C6H4(CHBr2)2 + 2 NaI → C6H4(\dCHBr)2 + 2 NaBr + I2
 * C6H4(\dCHBr)2 → C6H4(CHBr)2

Cycloadditions of these xylylenes provides a pathway to acenes.