Reactive compounds with three-membered rings, such as borirenes,[1] phosphirenes,[2] or the silicon and germanium analogues of the cyclopropenylium ion,[3] are particularly challenging to synthesize. Apart from thiirenium salts,[4] seleniranium ions which play a key role in the asymmetric synthesis with chiral diselenides have also been investigated.[5] Selenirenium ions have been postulated as principal intermediates in addition reactions ...
