The reaction of thiocarbamoyl isoselenocyanate with a carbanion gave 1-thia-6-oxa-6aλ4-seleno-3-azapentalene, which has a hypervalent selenium, as the major product. The by-products 3-diacylmethylidene-5-dimethylamino-3H-1,2,4-dithiazole and thiocarbamate thioanhydride were also formed.