Synthesis and Ring Opening of Fused Steroidal Aziridines

A search for synthetic approaches to fused steroidal aziridines lead to a synthesis of 2β,3β-iminocholestane (IV) in 75% from 2-cholestene. Addition of iodine isocyanate to 2-cholestene gave the trans diaxial 3α-iodo-2β-cholestanyl isocyanate (I) which can be converted into methyl 3α-iodo-2β-cholestanylcarbamate (II) or the iodoamine hydriodide III upon heating with methanol or aqueous hydroiodic acid, respectively. Both II and III give the aziridine IV upon treatment with base. The structure of IV was proved by n.m.r. spectra and by opening of the aziridine with acetic acid and subsequent acetylation to 3α-acetoxy-2β-acetamidocholestane (VIII) prepared independently. The stereochemistry of ring opening of a 2,3-fused three-membered ring in steroids is discussed. Several derivatives of IV were prepared.