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.