1. N. F. Kucherova, L. N. Borisova, N. M. Sharkova, and V. A. Zagorevskii, Khim. Geterotsikl. Soedin., No. 9, 1219 (1970).
2. J. B. Hall, J. B. Bremner, and E. J. Browne, Heterocycles, 26, 1573 (1987).
3. N. S. Prostakov, A. V. Varlamov, A. A. Fomichev, N. D. Sergeeva, T. N. Borisova, and Annan Husein, Summaries of Papers Presented at the 4th All-Union Conference on the Chemistry of Nitrogen-Containing Heterocyclic Compounds [in Russian], Novosibirsk (1987), p. 190.
4. L. S. Stanishevskii, I. G. Tishchenko, and A. Ya. Guzikov, Zh. Org. Khim., 7, 2612 (1971).