A New Electrochemical System for Stereoselective Allylic Hydroxylation of Cholesteryl Acetate with Dioxygen Induced by Iron Picolinate Complexes

Abstract

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.

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

“…This trend suggests that the stereoselectivity depends upon steric factors of the substrate, as we reported before, 21) e.g., steric hindrance of the 10-methyl group, or the conformation of the B-ring. This view is supported by the fact that the stereoselectivity in hydroxylation is slightly less than, but in a similar direction to, that in the hydroxylation of cholesteryl acetate 1.…”

“…The results are shown in Chart 2 and Table 1. As we reported before, 21) this condition is not effective for reduction of dioxygen and it permits the one-electron reduction of Fe III (PA) 3 in acetonitrile. Furthermore, because significant amount of the substrates were recovered, it can be considered that overoxidation caused by disappearance of the substrates was avoided.…”

“…[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][23][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.…”

Direct electrochemical acetoxylation of cholesterol at the allylic position

“…In the third system 3,5,6-trihydroxycholesterol, 7-hydroxycholesterol, 5,6-epoxycholesterol, 7-oxocholesterol, and three unidentified substances were reported as products. A new electrochemical system for oxidation of cholesterol acetate with O 2 induced by iron picolinate complexes, giving mainly the 7-hydroxylated products with high stereoselectivity (the ratio 7a-OH:7b-OH greater than 100:9), was recently described [20]. Here, we report that cholesterol can undergo direct electrochemical oxidation in glacial acetic acid.…”

A selective electrochemical method of glycosylation of 3β-hydroxy-Δ5-steroids

“…Also electrochemical oxidation of cholesteryl acetate induced by dioxygen and iron picolinate complexes afforded mostly 7-hydroxylated products. 8 Recently described direct electrooxidation of cholesterol on carbon electrode in acetonitrile produced cholesta-4,6-dien-3-one. 9, 10 We have previously reported direct electrochemical oxidation of cholesterol on platinum electrode in glacial acetic acid.…”