Synthesis of 9,11-Secosteroids Pinnisterol E, Glaciasterol B, and 6-Keto-aplidiasterol B.

A 10-step gram-scale synthesis of 9,11-secosteroid pinnisterol E from the inexpensive ergosterol is reported. This synthesis features a series of highly selective redox transformations such as regioselective olefin hydrogenation (PtO 2 ), acid-sensitive endoperoxide reduction (Al-Ni alloy, Zn), and regio- and diastereoselective dienone oxidation. The robustness of this strategy is clearly demonstrated through the formal synthesis of 11(9 → 7) abeo -steroid pleurocin B and the divergent synthesis of 9,11-secosteroids glaciasterol B and 6-keto-aplidiasterol B from the inexpensive cholesterol.