1. A preliminary report of this work was presented at the 9th International Congress of Heterocyclic Chemistry, Tokyo, Japan, August 1983.
2. F. Bossert and R. Goennert, German Patent 954599 (1956).
3. Chem. Abstr., 53, 6257e (1959).
4. M. von Strandtmann, M. P. Cohen, S. Klutchko, J. Shavel, U. S. Patent 3816466 (1974).