REACTIONS OF PHOSPHINES WITH ACETYLENES .17. FORMATION AND STEREOCHEMISTRY OF 1,2-DICYANO-2-PHOSPHONIAETHANESULPHONATE BETAINES

The initial intermediate in the reaction of triarylphosphines with cyanoacetylenes may be trapped as an adduct with water and sulphur dioxide. The structures of the adducts are shown to be phosphoniaethanesulpnonate betaines. Vicinal n.m.r. coupling constants show that in trifluoroacetic acid solution the betaines from dicyanoacetylene are held in a rigid conformation of the threo configuration. However, in dimethyl sulphoxide solution the coupling is removed by a slow proton exchange process.