A Straightforward Methodology for Construction of [5,6] and [6,6] Spiroketal Moieties Around the A-ring of 5α and 5β-Steroids. NMR and X-ray Characterization

The construction of 1,6-dioxaspiro[4.5]decane and 1,7dioxaspiro[5.5]undecane moieties around the A ring of 5 and 5steroids are described. The addition of lithium acetylides derived from 3-benzyloxy-1-propyne or 4-benzyloxy-1-butyne to steroid lactones produced benzylated en-yne adducts bearing an enol ether moiety. Chemoselective triple bond hydrogenation and benzyl ether hydrogenolysis leaving the enol ether unaffected allows the spontaneous cyclization to the corresponding spiroketals. NMR and X-Ray studies corroborated the target structures.