The synthetic application of the new reagent, 1,2-bis[(Z)-2-(vinylsulfanyl)ethenyl] diselane, was described for the first time. This reagent was obtained in high yield by a chemo-, regio- and stereoselective reaction of 2-bromomethyl-1,3-thiaselenole with organylthiolate anions. The diselane is a synthon of two equivalents of the (Z)-H₂CCHSCHCHSe⁻ anion. This anion was involved in nucleophilic substitution reactions with organyl halides and dihalides affording a wide range of first representatives of polyunsaturated sulfur/selenium-containing compounds, (Z)-2-(organylselanyl)ethenyl vinyl sulfides 2a–j in 88–97% yield and disubstituted symmetrical Z,Z-isomers of tetraenes 3a,b in 90–92% yields. Regio- and stereoselective nucleophilic addition to various acetylenes were carried out. The reaction with unsubstituted acetylene afforded vinyl (Z)-2-(vinylselanyl)ethenylsulfide in 88% yield. Methyl and ethyl (Z)-3-{[(Z)-2-(vinylsulfanyl)ethenyl]selanyl}-2-propenoates were obtained in 87% yield from alkyl propiolates. The reaction with dialkyl 2-butynedioates led to polyunsaturated products 5a,b in 76–78% yield.