The Efficient and Enantiospecific Total Synthesis of Cyclopenta[b]phenanthrenes Structurally-related to Neurosteroids.
We report an efficient synthesis of cyclopenta[b]phenanthrenes functionalized at C-3 and C-8 from an optically pure Hajos-Parrish ketone. The key step is a neutral alumina catalyzed Michael addition of a Hajos-Parrish ketone derivative (4) to 1,7-octadien-3-one (2) in 98% yield. This Michael addition product went through Krapcho decarbomethoxylation, aldol condensation, lithium liquid ammonia reduction, Wacker oxidation and acid catalyzed cyclization to form cyclopenta[b]phenanthrene (1a) in 37% overall yield for the 7 steps.
Department of Developmental Biology, Washington University in St. Louis, School of Medicine, Campus Box 8103, 660 S. Euclid Ave., St. Louis, Missourri 63110.
Mingxing
M
Qian
Douglas F
DF
Covey