1. H. Beyer, Z. Chem., 9, 361 (1969).
2. S. Radl, Janssen Chim. Acta, 5, 3 (1987).
3. E. Bulka, W. D. Pfeiffer, C. Tröltsch, E. Dilk, H. Gartner, and D. Daniel, Collect. Czech. Chem. Commun., 43, 1227 (1978).
4. H. Johne, K. Seifert, S. Johne, and E. Bulka, Pharmazie, 33, 259 (1978).
5. S. F. Kahlilova and I. A. Poplavskaya, Izv. Akad. Nauk KazSSR, Ser. Khim., No. 1, 56 (1984).