Benzene also undergoes addition, but with a different radical mechanism, eg
C6H6 + 3Cl2 = C6H6Cl6
se also
Benzene as Dienophile in the Diels-Alder Reaction
Angewandte Chemie International Edition in English
Volume 14, Issue 3, Date: March 1975, Pages: 181-182
Wolfgang Jarre, Dieter Bieniek, Friedhelm Korte