The electroreduction of several fused [1,3,4]-thiadiazinium salts on mercury pool cathode in an aprotic medium has been studied. In preparative experiments using dimethylformamide 0.2 M in lithium perchlorate as the electrolyte, the [1,3,4]-thiadiazinium salts 1-3 formed a mixture of the corresponding fused pyrazoles and ketimines. On the basis of results of preparative electrolyses (products and reaction