Allylic hydroperoxides formed by singlet oxygenation of cholest-5-en-3-one

Abstract

Cholest-5-en-3-one (I) reacts with singlet oxygen to give the hemiperketal (II)(ca. 55%), the epimeric 6β- and 6α-hydroperoxides (III) and (IV)(ca. 30 and 8% respectively), and the dione (V)(ca. 7%). The hemiperketal (II) does not undergo an allylic rearrangement in solution, but the hydroperoxides (III) and (IV) epimerise by a radical chain mechanism. [graphic omitted]

Stereochemical problems connected with this system have been probed by carrying out parallel experiments and molecular mechanics calculations on the corresponding derivatives of methylocta-hydronaphthalenone as model compounds.