19-Nor and aromatic steroids. Part II. Cleavage of 3-oxygenated 4β,19-ethers in the pregnane series leading to 19-norprogesterone
Abstract
Treatment of pregn-4-ene-3β,20β-diol with m-chloroperbenzoic acid gave the 4β,5β-epoxide (IIa), which was separated from the 4α,5α-isomer by recrystallisation. Acetylation of the β-epoxide (IIa) followed by hydrogenation over platinum oxide in acetic acid gave 3β,20β-diacetoxy-5α-pregnan-4β-ol, readily converted into the 4β,19-epoxide (XIIa) by reaction with lead tetra-acetate. Oxidation then gave the epoxy-dione (XIII), cleavage of which with boron trifluoride in acetic anhydride gave mainly 4α,19-diacetoxypregnane-3,20-dione. Careful hydrolysis in methanol for 10 min gave the 4α,19-diol (XIVb); this was converted into 19-hydroxyprogesterone (Ic), which can be converted into 19-norprogesterone.