Radical species generated from 5-aryl-substituted 1-ethyl-2,3-dicyano-1,4-diazinium salts by action of sodium iodide undergo dimerization into [2,2?]bipyrazinyl derivatives, as evidenced by NMR and X-ray crystallography data. The pyrazinyl radicals can also be involved into the addition reaction on the C-C triple bond, thus demonstrating a new synthetic route to modify the structure of pyrazines. The structures of E- and Z-isomers of 1-(1?,2?-dihydropyrazinyl-2?)-2-iodoethenes have been proved by 1H and 13C NMR spectroscopy and X-ray analysis