1. R. J. Sundberg, in: O. Meth-Cohn (editor), Best Synthetic Methods, Academic Press, London (1996), p. 7.
2. W. Leimgruber and A. D. Batcho, in: Third International Congress of Heterocyclic Chemistry, Japan, August 23–27, 1971, p. 462.
3. L. I. Kruse, Heterocycles, 16, 1119 (1981).
4. W. Leimgruber and A. D. Batcho, in: R. L. Danheiser (editor), Organic Synthesis, John Wiley & Sons, New York, Coll. vol. 7, p. 34 (1990); [vol. 65 (1985), p. 214].
5. R. D. Clark and D. B. Repke, Heterocycles, 22, 1119 (1984).