Studies in the steroid group. Part LXXX. Preparation of 2- and 16-oxo-, and 3,16- and 2,16-dioxo-5α-androstane, and 2-oxo-5α-cholestane

Abstract

16-Oxo-5α-androstanes are readily obtained from the 17-ketones in three stages, viz., condensation with benzaldehyde to 16-benzylidene-17-ketones, reduction with lithium aluminium hydride–aluminium chloride to 16-benzylidene-androstanes, and ozonolysis. This sequence is not suitable for the 3 → 2 transposition of oxo-groups in ring-A. Here the 2-arylidene-6-ketones are reduced with sodium borohydride and acetylated before ozonolysis: the acetoxy-groups of the 3β-acetoxy-2-ketones are removed by reduction with zinc and acetic acid. With 5α-androstane-3,17-dione the longer route afforded 5α-androstane-2,16-dione in 24% yield overall.