1. D. S. Tarbell and M. A. McCall, J. Am. Chem. Soc.,74, 48 (1952).
2. M. Kocevar, B. Stanovnik, and M. Tisler, Croat. Chem. Acta,45, 457 (1973).
3. V. P. Litvinov, V. E. Solodovnikov, A. V. Anisimov, and E. A. Viktorova, Khim. Geterotsikl. Soedin., No. 6, 851 (1989).
4. K. Undheim and K. R. Reistad, Acta Chem. Scand.,24, 2949 (1970).
5. G. A. Ulsaker and K. Undheim, Acta Chem. Scand.,B29, 853 (19/5).