Cyclooligomerization of the dibromodihydrobenzocyclobutene (I) results in the formation of the dimers and trimers (II) ‐ (IV).

Reaction of 1 ,l-dibrom0-2-methylpropene with butyl-lithium at -100 "C, followed by treatment with a copper(i) complex produces the ate-type complex of the corresponding copper carbenoid, which cyclizes upon warming to afford decamethyl[5]radialene together with octamethyl[4]radialene; the structure of decamethyl[5]radialene has been established by X-ray analysis.