ALLYLIC HYDROPEROXIDES FORMED BY SINGLET OXYGENATION OF CHOLEST-5-EN-3-ONE

Cholest-5-en-3-one (I) reacts with singlet oxygen to give the hemiperketal (II) (ca. 55%), the epimeric 6β- and 6a-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. Stereochemical problems connected with this system have been probed by carrying out parallel experiments and molecular mechanics calculations on the corresponding derivatives of methyloctahydronaphthalenone as model compounds.