Benzothiazolium salts reduction

Benzothiazolium salts in aqueous solution with tetraethylammonium perchlorate as supporting electrolyte are reduced in two one-electron steps.270 The first produces a radical that dimerizes with a radical-substrate reaction as the rate-determining step. The product is dimerized in the 2-position. Reduction at the potential of the second step produces the 2,3-dihydrobenzo-thiazole. 

Benzothiazoles are rather more prone to reductive decyclization than are thiazoles, although it is possible to form benzothiazolines (224) through the sodium borohydride reduction of benzothiazolium salts (223). On hydrolysis these products yield 2-aminothiophenols (225). Prolonged exposure of benzothiazolines to excess sodium borohydride also causes ring opening to aminothiophenols, as does reaction with LAH. In this last case the substrates for reduction may be benzothiazoles (226), which presumably initially form benzothiazolines with the reagent (Scheme 18). ... 

The quaternary salts of A -heterocycles are readily reduced and often give reversible one-electron reduction waves, as, for example, with pyridium salts [122]. Dimers have been obtained by this pathway e.g. from acridizinium and benzothiazolium salts [116]. Such processes are particularly important both with biological substrates (e.g. NAD is reported to give essentially 4,4 -dimers on reduction) [123] and in the monoelectronic reduction of di-cations such as dipyridinium and a variety of diaza polycyclic aromatic di-cations [124]. 

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