[n]Radialenes consisting of an n-membered ring and n exocyclic double bonds are a class of cyclic π-conjugated molecules. They have much attention from the viewpoint of their unique molecular and electronic structures due to the cyclic cross-conjugation systems. Various derivatives substituted at the terminal position of the exomethylene carbons were synthesized so far. The derivatives and analogs of [n]radialene substituted with redox-active 1,3-dithiol-2-ylidenes (DTs) (n=4-6) are of interest as multistep redox systems that n DT sites work. Among them, DT[5]radialene derivatives (9) indicate a unusual redox behavior. However, the detailed studies on the synthesis, structural and electronic properties of 9 are in the process of development for the functional materials. In this paper, we revealed the molecular and electronic structures, significant redox behavior, the reactivity of 9 and its oxidized species. Herein, we introduce the synthesis and redox properties of DT[n]radialenes: hydration reaction of (9)⁴⁺ and the molecular structure of its products (13, 14, 15), the possible mechanism ; the synthesis and properties of analogs bearing aromatic rings (20) and π-extended derivatives (22) of 9; the synthesis and redox properties of TTF-fused donor exhibiting a simultaneous four-or eight-electron transfer (24, 25, 27, 33, 34, 35, 36).