19-Hydroxy steroids. V1. 3β,7α,19-trihydroxy-5-androsten-17 one 3,19-diacetate: A potential precursor in the biosynthesis of B-ring unsaturated estrogens

Selective Allylic Hydroxylation of Octahydronaphthalene Derivatives with a Bridgehead Double Bond Using Electrochemical Method with Iron Picolinate Complexes

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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 Discussion

The substrates 5b-7b were prepared by benzoylation of the corresponding octahydronaphthalenols 5a-7a.

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“…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.…”