No abstract

that a radical mechanism is operative in these reactions.No isomerization at C-14 occurred when the solvent, cyclohexane, was replaced by /-butyl alcohol or methyl alcohol. Other hydrocarbon solvents, capable of dissolving mercuric bromide (e.g., hexane) could however replace cyclohexane.Since we assumed that the bromine radicals were responsible for the epimerization reaction, we have tried to use other sources of these radicals. A cyclohexane solution of 14a steroid lb was thus irradiated in the presence of bromine and of bromotrichloromethane. No more than 10% of the epimerized 14/3 derivative 2b was formed. However, irradiation with the same light source in the presence of 0.15 equiv of N-bromosuccinimide resulted in a 50% conversion of 17/3acetoxy derivative lb to its 14/3 epimer 2b, and in the presence of 1 equiv in a 90% conversion. The 17-ketone If was also epimerized to the 14/3-17-ketone 2f in 50% yield when irradiated in cyclohexane solution in the presence of 1.5 equiv of N-bromosuccinimide. Work on further applications and on the mechanism of this isomerization reaction is now in progress.Acknowledgment. This work was supported by a grant of the Ministry of Commerce and Industry of Israel.(9) The solution irradiated contained equivalent concentrations of the phenol and of the 14a-steroid lb (3 mM each). The phenol did not act as a uv filter as indicated by irradiation of the same compound, lb (3 mAf), in the presence of much higher concentrations of benzene (30 mAf) which resulted in 80% epimerization to 2b.

No abstract

Radicals by Copper(II) Complexes [7. Am. Chem. Soc., 90, 4616 (1968)].