Reactions of Dichlorothionitronium Hexafluoroarsenate(V) with Alkynes & Alkenes

The dithionitronium cation (SNS + ) has been shown to undergo completely general, concerted cycloadditions with a wide variety of unsaturated main-group species to give heterocyclic products in quantitative yields. The isolobality of the frontier molecular orbitals of the dichlorothionitronium cation (ClSNSCl + ) with those of SNS + led us to predict that this cation would undergo concerted cycloadditions under similar conditions. This has been confirmed in its reactions with acetylene and ethylene. Dichlorothionitronium hexafluoroarsenate(V) (ClSNSCl + AsF 6 - ) reacts with acetylene in liquid sulphur dioxide to produce 1,3,2-dithiazolium hexafluoroarsenate(V) quantitatively via initial cycloaddition followed by SO 2 -mediated chlorine abstraction and aromatisation. Analogously, cycloaddition also occurs with ethylene, though without subsequent chlorine abstraction. This has enabled a novel 1,3-dichloro-1,3,2-dithiazolidinium salt to be isolated in quantitative yield. The characterisation of this product by a variety of spectroscopic techniques will be discussed, together with recent developments in the chemistry of this and related systems.