1. C. L. Habraken and P. Cohen-Fernandes, Second International Congress of Heterocyclic Chemistry, Montpellier, France, July 7-11, 1969.
2. M. D. Coburn, Second International Congress of Heterocyclic Chemistry, Montpellier, France, July 7-11, 1969.
3. J. Heterocyclic Chem., 7, 345 (1970).