[3]Radialene or trimethylenecyclopropane was synthesised in 1965.Reported derivatives are triquinocyclopropanes, salts of trimethylenecyclopropane dianions, tris(thioxanthen-9-ylidene)cyclopropane, tris(fluoren-9-ylidene)cyclopropane and hexakis(trimethylsilylethynyl)[3]radialene.