Iodonium derivatives of heterocyclic compounds

A method for the preparation of phenyliodonium derivatives of pyrazoles was developed. The reaction of pyrazole and 3,5-dimethyl- and 3,5-diphenylpyrazoles with phenyl iodosoacetate in the presence of p-toluenesulfonic acid gives pyrazole-4-phenyliodonium tosylates, which are converted to pyrazole-4-phenyliodonium betaines on treatment with alkali. The tosylates are converted to pyrazole-4-phenyliodonium chlorides, bromides, and iodides by exchange reactions, and pyrazole-4-phenyliodonium fluorides and borofluorides are obtained by reaction of the betaines with hydrofluoric and fluoboric acids. The ionization constants for a number of phenyliodonium derivatives of pyrazoles were calculated on the basis of the electronic absorption spectra. The 4-phenyliodonium grouping increases the acidity of pyrazoles by 4.5–5 orders of magnitude.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 245–248, February, 1973.