2,4-Dioxathiazolidine derivatives (7) have been obtained in synthetically useful yields by the condensations of easily available 1-substituted-4,4,6-trimethyl-1,4-dihydropyrimidine-2(3H) thione derivatives (4) and α-halogenated carboxylic acids in aqueous medium. The condensations of 4 with α-haloketones in ethanol containing cone HCl furnish 2-oxa-4-thiazolines (8). The condensations of N,N-dialkyl-N'-aryl
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