3-Methylbenzothiazolium salts were allowed to react with superoxide to afford dimeric bis[o-(N-formyl-N-methylamino)phenyl]disulfides and 3-methyl-2-benzothiazolones. The reaction was applied to monocyclic thiazolium salts, and novel ten-membered ring compounds were formed whose structures were elucidated by X-ray crystallographic analysis. These results prompted us to alternative synthesis of the ring compound, and bithiazolium salts were revealed to afford them by the reaction with superoxide.