1. H. U. Kibbel, U. Ohnmacht and J. Teller; Ger. (East) Pat. 148341 (1981) (Chem. Abstr., 1982, 96, 20092).
2. K. Gewald, U. Hain and G. Roemhild; Ger. (East) Pat. 152937 (1981) (Chem. Abstr., 1982, 97, 6290).
3. P. Hansen and W. Liebich; Ger. (East) Pat. 154987 (1982) (Chem. Abstr., 1983, 98, 34577).
4. Reactions with heterocyclic diazonium salts: novel synthesis of pyrazolo[4,3-c]pyridazines and of pyrazolo[4,3-c]pyrazoles