Reductive dimerization of benzothiazolium salts

Three different types of reaction products were obtained from the reduction of 2-substituted 3-methylbenzothiazolium salts using Na : Hg (1 wt%). Depending on the 2-substituents, two types of dimeric compounds were obtained: the 2-cyclohexyl-, 2-phenyl-, and 2-( p -tolyl)-substituted species are reduced to the corresponding 2,2′-bibenzo[ d ]thiazoles, while their 2-(( p -OMe)C 6 H 4 )- and 2-(( p -NMe 2 )C 6 H 4 )-substituted derivatives afford cis -[1,4]benzothiazino[3,2- b ][1,4]benzothiazines. Furthermore, in the presence of molecular O 2 , new disulfide derivatives were obtained from the bibenzo[ d ]thiazoles. The products were obtained in a moderate to good yield, and the structures were confirmed using single-crystal X-ray diffraction. The electrochemistry and further reactivity towards different oxidants of the dimeric compounds were studied; the 2,2′-bibenzo[ d ]thiazoles show oxidation potentials similar to that of ferrocene and are converted back to the corresponding benzothiazolium cations by mild oxidants such as TCNQ. In contrast, the benzothiazino-benzothiazines show no oxidations in the solvent window of THF. A simple, straightforward preparation of two types of dimeric products, bi-benzothiazoles, and benzothiazino-benzothiazines, from the reduction reaction of 2-substituted 3-methylbenzothiazolium salts.