Synthesis and radical oxidation of steroidal 1-oxo-5α-alcohols

Abstract

A new synthetic approach is described for the preparation of steroidal 1-oxo-5α-alcohols. A key step in the synthesis was the [2,3]sigmatropic rearrangement of allylic 3α-selenide ensuring the introduction of the desired functional groups at C-1 and C-5. The radical oxidation of 1-oxo-5α-alcohol was shown to proceed with the formation of 5,10-seco steroid. Its structural assignment was based on NMR and CD spectroscopic studies.

Synthesis of Swinhoeisterol A, Dankasterone A and B, and Periconiastone A by Radical Framework Reconstruction

“…Following this plan, we chose our previously described 14-hydroxy steroid 6 , which we obtained from ergosterol (not shown) in four steps and 42% overall yield, to explore several options for the generation of the 14-alkoxy radical. When treating 6 with Pb­(OAc) 4 and I 2 under CaCO 3 -buffered conditions in refluxing benzene, we obtained a complex mixture containing four major products 7 – 10 (Table , entry 1). Careful separation and analysis confirmed the formation of two 13(14 → 8) abeo -ergostanes 7 and 8 as minor products of the reaction (for X-ray crystallographic data, see Supporting Information), wherein 8 is the 7-iodo derivative of 7 .…”