1. L. S. Teslov, Khim. Prir. Soedin., 582 (1979).
2. É. T. Oganesyan, A. A. Shinkarenko, and V. A. Bandyukova, Khim. Prir. Soedin., 212 (1968).
3. J. Karliner and C. Djerassi, J. Org. Chem.,31, 1945 (1966).
4. L. Fieser and M. Fieser, Steroids, Reinhold, New York (1959).
5. A. G. Panosyan and V. A. Mnatsakanyan, Khim. Prir. Soedin., 59 (1977).