1. V. M. Potapov, G. V. Kiryushkina, I. K. Taleborovskaya, N. N. Shepet'ko, and I. I. Radushnova, Zh. Organ. Khim., 9, 2134 (1973).
2. C. Djerassi and D. Herbst, J. Org. Chem., 26, 4657 (1961).
3. C. Emeis, L. Oosterhoff, and G. De Vries, Proc. Roy. Soc., A297, 54 (1967).
4. J. V. Burakevich and C. Djerassi, J. Am. Chem. Soc., 87, 51 (1965).
5. C. Djerassi and K. Undheim, J. Am. Chem. Soc., 82, 5755 (1960).