1. U. A. Baltaev and N. K. Abubakirov, Khim. Prir. Soedin., 681 (1987).
2. U. A. Baltaev, Khim. Prir. Soedin., No. 6, 806 (1991).
3. J. P. Girault, R. Lafont, E. Varga, Z. Hajdu, I. Herke, and K. Szendrai, Phytochemistry,27, No. 3, 737 (1988).
4. T. Takemoto, Y. Hikino, I. Arai, and H. Hikino, Tetrahedron Lett., No. 37, 4061 (1968).