Synthesis of (25R)-5α-Cholestane-3β,6β,15α,16β,26-pentol, a Cytostatic Starfish Steroid^†

The synthesis of (25R)-5α-cholestane-3β,6β,15α,16β,26-pentol (1a), a marine cytostatic steroid, has been achieved in 13 steps (7.8% overall yield) starting from commercially available diosgenin (2). A key step in the synthesis was the dimethyldioxirane oxidation of the enolsilane 16 to introduce the 15α-hydroxy group in the D ring.