Treatment of 1-chloro-2,2-bis(diethylamino)ethene (1) with elemental selenium in refluxing benzene gave 4,8-bis[bis(diethylamino)methylene]-1,2,3,5,6,7-hexaselenacyclooctane (4) in 60% yield. The structure of 4 was determined by X-ray diffraction analysis. Compound 4 behaves as 2,2-bis(diethylamino)-2-ethylium-1-diselenocarboxylate (3) toward a range of reagents. Thus, 4 reacted with Met dimethyl acetylenedicarboxylate, and elemental sulfur, under mild conditions, to give the carbenium iodide 5a, the 1,3-diselenole 6a, and the dithiocarboxylate 2, respectively, in high yields, while the thermolysis in refluxing a-dichlorobenzene afforded the alpha-diselenoamide 7. Evidence for the dissociation of 4 into 3 in solution is provided by IR, UV/vis, and H-1-, C-13-, and Se-77- NMR spectra.