.S)(NR.sup.3R.sup.4)] and, for example, the heterocyclic compounds##STR00006## ##STR00007##where the substituentsR.sup.1 to R.sup.6 and R.sup.1' to R.sup.4' are as defined above for the cations.The reaction is preferably carried out under inert-gas conditions in an organic solvent, for example dichloromethane, a dialkyl ether, for example diethyl ether, ethyl acetate, nitromethane or acetonitrile,