Stereoselective synthesis of (22R,23R,24S)-3β-Hydroxy-5-ene-22,23-dihydroxy-24-methyl-cholestane: A Brassinolide Intermediate from 16-Dehydropregnenolone Acetate

Article abstract of DOI:10.1016/S0040-4020(01)86968-4

A new synthesis of the important aldehyde 1 from easily available 16-Dehydropregnenolone acetate (16-DPA) in high yield is described.The aldehyde 1 is converted to triol 24, involving a stereoselective generation of all the four chiral centers in the brassinolide side chain.The important features of this synthesis is stereospecific generation of the acetate 14 through ene reaction using three different catalysts as well as regioselective wittig reaction on the acetoxy aldehyde 20.Conversion of triol 24 to brassinolide is known, hence this constitutes a formal total synthesis of brassinolide.