Synthesis of steroidal D-ring fused pyrazolines: study of regiochemistry of addition.

The addition of diphenylnitrilimine and C-o-chlorodiphenylnitrilimine to 3 beta-hydroxyandrost-5,16-diene (3b) produced a 1/1 ratio of regioisomeric, 1,3-diaryl-2-pyrazolines (6a, 7a and 6b, 7b), whereas the addition of N-o-chlorodiphenylnitrilimine gave a 5/1 ratio in favor of the [17 alpha, 16 alpha-d] regioisomer (7c). To further delineate the factors governing the regiochemistry of addition of diphenylnitrilimines to steroid 16-enes, additions were carried out on 16-acetyl-5 alpha-androst-16-ene (5b) and 1-acetylcyclopentene (10).