1. T. L. Popper and A. S. Watnick, “Annual Reports in Medicinal Chemistry” p. 192, 1969 and p. 162, 1970.
2. Steroids with heteroatoms in the cyclopentenophenanthrene skeleton and those with additional heterocyclic ring built on the steroid nucleus have both been frequently referred to as heterocyclic steroids. To avoid confusion, we propose that the former class of steroids be named as heterocyclic steroids and the latter as steroidal heterocycles.
3. Synthesis of new heterocyclic derivatives of estradiol
4. M. Stefanović, Lj. Kristić and S. Mladenović, Tetrahedron Letters, 3311 (1971).