Reactions of stereoselective addition of selenium dibromide and monobromide to acetylene

Abstract

The reaction of selenium tetrabromide with acetylene afforded bis(2-bromovinyl)selenium dibromide as a mixture of isomers [1]. No information existed on the reaction of selenium dibromide and monobromude with acetylene. We perform systematic research on the reactions of selenium halides with unsaturated compounds [2–12]. It was shown for the first time in [2, 3] that selenium dichloride and dibromide were suitable for the preparation of organoselenium compounds. By the addition of selenium dichloride and dibromide to divinyl sulfide, diorganyldiethynylsilanes and –germanes new heterocyclic compounds were synthesized [2–12]. We performed for the first time the reactions of selenium dibromide and monobromide with acetylene. They proceed as a stereoselective anti-addition with the formation of a previously unknown E,E-bis(2bromovinyl)-selenide (I) in 90–98% yield. of selenium monobromide with acetylene in chloroform at 30–40°C resulted in selenide I in 98% yield (calculated on the taken selenium monobromide) and was accompanied by the elemination of elemental selenium. The reactions were characterized by high stereoselectivity: exclusively compound of the E,E-configuration was obtained. This stereoslectivity might originate from the involvement into the reaction cyclic intermediates A, B. The formation of analogous intermediates in the reactions of electrophilic addition of compounds with a selenium–halogen bond to alkynes was previously established [13].