Di(tert-butyl)-1,2-benzoquinone reacted with 1,2,3-trimethylbenzimidazolium iodide led to the formation of 2,2' -spirobi(4,6-di(tert-butyl)-1,3-benzodioxole). The reaction mechanism was suggested. The structure of 2,2' -spirobi(4,6-di(tert-butyl)-1,3-benzodioxole) was established by means of X-ray diffraction analysis. Scheme 1. The chemistry of sterically-hindered O-quinones is versatile and rich in unexpected paths in reactions with methylene-active compounds. We recently revealed that the reaction of the sterically-hindered O-quinones with quinaldine derivatives resulted in the formation of (quino- lin-2-yl)-1,3-tropolones (1-3). Reactions of 3,5-di(tert- butyl)-1,2-benzoquinone with 2-methylbenzimidazole derivatives gave rise to polycyclic isoquinoline derivatives (4). We extended this reaction to benzimidazolium salts, and the study of reaction products obtained from 3,5-di- (tert-butyl)-1,2-benzoquinone (I) and a salt of 1,2,3-tri- methylbenzimidazolium II by X-ray diffraction analysis demonstrated the formation of 2,2'-spirobi(4,6-di(tert- butyl)-1,3-benzodioxole) (III) in considerably high yield (65-70%) (Scheme 1). The structure of 2,2'-spirobi(4,6-di(tert-butyl)-1,3- benzodioxole) (III) has been established by X-ray crystallography and is shown on the figure. The main interatomic distances and bond angles are compiled in the table. The presumed mechanism of compound III formation is given in Scheme 2. In the first stage of the reaction quinone I adds to the N-methyl group of the benzimidazolium resulting in the formation of adduct A, whose oxidation with initial quinone I may give 3-(4,6-di(tert-butyl)-1,3-benzodioxol- 2-yl)-1,2-dimethyl-3H-benzimidazolium iodide B. Further transformation occurs probably through the addition of the second quinone I molecule to salt B leading to intermediate compound C followed by elimination of a molecule of 1,2-dimethylbenzimidazolium iodide (IV) and thus giving rise to reaction product III.