摘要:
The 5 alpha- and 5 beta-oriented Delta(3)-double bond isomers 8, 9 of the widely used progestin desogestrel (7) were synthesized. Wittig olefination reaction of the 5 alpha-intermediate 12 showed a dramatically reduced reaction rate compared with the olefination of the 5 beta-intermediate 13. Computational studies suggest that different energies of the intermediary 1,2-oxaphosphetanes may, at least partially, have been the reason for-this phenomenon. (C) 1998 by Elsevier Science Inc.