The oxygenation reaction of cholesteryl acetate 1 was examined with the Fe(III)(PA)(3)/O(2)/MeCN system using an electrochemical method. The constant potential technique gave mainly the 7-hydroxylated product stereoselectively, along with the 7-oxo product. This oxygenation system is mechanistically unique, requiring iron catalyst, dioxygen, and both cathode and anode.

Oxygenation reactions are very important in steroid metabolism and biosynthesis.1-3) Many investigations on biomimetic oxygenation systems using iron(III) picolinate (Fe III (PA) 3 ) or iron(II) picolinate (Fe II (PA) 2 ) complexes as catalysts have been reported under various conditions and in various solvents, [4][5][6][7][8] but direct 7a-hydroxylation is not easy and most reported allylic hydroxylations involve multistep reactions via other functionalized compounds [9][10][11][12][13][14] or afford low yield or stereoselectivity. [15][16][17] We have been developing a 7a-hydroxylation system for steroids, [18][19][20] and we reported in a preceding paper that the combination of electrolysis and the Fe III (PA) 3 /O 2 /CH 3 CN system gave good results in the hydroxylation of cholesteryl acetate. 21)On the other hand, functionalization, especially oxygenation, of octahydronaphthalenes or decalin derivatives is also very important because many bioactive or natural compounds contain a skeleton resembling the AB fused ring of cholesterol.22-24) Therefore, we wished to identify the required structural factors for regio-and stereoselective direct 7a-hydroxylation of steroids by our electrochemical method, as well as to extend the range of applicability of this method for allylic a-hydroxylation of small cyclic compounds.In this report, we describe the iron picolinate-induced hydroxylation reactions of octahydronaphthalene derivatives 5b, 6b and 7b as simple models for allylic oxygenation of steroids or other decalin derivatives. Results and DiscussionThe substrates 5b-7b were prepared by benzoylation of the corresponding octahydronaphthalenols 5a-7a. [25][26][27] Both 5b and 6b have an alkene moiety at a similar position to C5-C6 of cholesterol. However, the double bond of 7b is not located at the bridgehead of the fused ring. We applied Showa Pharmaceutical University; 3-3165 Higashi-tamagawagakuen, Machida, Tokyo 194-8543, Japan. Received October 23, 2004; accepted November 11, 2004; published online November 22, 2004 The combination of electrolysis and the Fe III (PA) 3 /O 2 /CH 3 CN system was investigated for allylic hydroxylation of octahydronaphthalene derivatives. Substrates with a bridgehead double bond gave the allylic alcohol with a a-preference, while non-bridgehead olefin did not react smoothly. This system is a useful tool for a a-selective allylic hydroxylation of octahydronaphthalene derivatives with a bridgehead double bond as model compounds for the AB fused ring of cholesterols.

Complexes. -Iron complexes of picolinic acid catalyze the stereoselective 7α-hydroxylation of cholesteryl acetate (I). Constant potential technique, cf. conditions A), yield better results than the constant current method. Fe(II) picolinate can also be used as catalyst. Stereoselective hydroxylation is also observed in the case of oleanolate (IV). -(OKAMOTO, I.; FUNAKI, W.; NAKAYA, K.; KOTANI, E.; TAKEYA*, T.; Chem. Pharm. Bull. 52 (2004) 6, 756-759; Showa Pharm. Univ., Machida, Tokyo 194, Japan; Eng.) -C. Oppel 46-181

Complexes. -Substrates with a bridgehead double bond like (I) give the allylic alcohol with α-preference, while the non-bridgehead olefin (V) does not react smoothly. The presented electrochemical method is a useful tool for α-selective allylic hydroxylation of octahydronaphthalene derivatives with a bridgehead double bond as model compounds for the AB fused ring of cholesterols. -(OKAMOTO, I.; FUNAKI, W.; NOBUCHIKA, S.; SAWAMURA, M.; KOTANI, E.; TAKEYA*, T.; Chem. Pharm. Bull. 53 (2005) 2, 248-252; Showa Pharm. Univ., Machida, Tokyo 194, Japan; Eng.) -H. Haber 31-108