1. A. M. Galushko and N. S. Dokunikhin, Zh. Org. Khim., 15, 575 (1979).
2. L. M. Gornostaev, G. F. Zeibert, and G. I. Zolotareva, Khim. Geterotsikl. Soedin., No. 7, 912 (1980).
3. German Patent No. 593671; Frdl., 20, 1310 (1934).
4. F. Kröhnke, Angew. Chem., No. 7, 317 (1963).
5. K. Nakanishi, Infrared Spectroscopy, Holden-Day, San Francisco (1962).