Highly Diastereoselective Epoxidation Of △～5-Steroids Derivatives Catalyzed By Polymer-Supported Metalloporphyrins

There is a growing interest in developing metalloporphyrin catalysts for epoxidation of unfunctionalized alkenes. Most of the studies have been focused on the relationship between porphyrin structure and the corresponding catalytic efficiency, or the promising application of those catalytic systems. In recent years the emphasis has been put on the catalyst stability and reuse. At the same time, β-epoxidation of Δ5-steroids has attracted a growing attention, it is partially because the 5β,6β-epoxidation are less accessible than corresponding 5a, 6a-isomers owing to the C(10)-angular methyl group of Δ5-steroids. Some success in p-epoxidation of Δ5-steroids has been achieved by using metal-based oxidants, e.g. chromium, manganese, or iron tetraphenylporphyrin/iodosobenzene, ruthenium(IV) tetramestylporphyrin or ruthenium(II) bioxazoline complex / molecular oxygen, iron(III) or titanium(III) acetylacetonates / hydrogen peroxide, potassium permanganate/metal sulfates, metal nitrates, or sodium perborate. The major drawbacks of these methods are that some catalysts of metal complexes are not easy to be prepared and are not stable and cannot be reused.Recently heterogenized manganese porphyrin catalysts have beenused to catalyze the epoxidation of general alkenes. There were reports on attachment of insoluble polymer support including surface-modified mesoporous molecular sieve (MCM-41), the Merrifield's peptide resin (MPR) and the polyethylene glycol (PEG) to give heterogeneous catalysts. Following line of this research, the results obtained in the highly diastereoselective epoxidation of A 5-steroids derivatives catalyzed by polymer-supported metalloporphyrins are reported.Manganese (III) 5,10,15-tris(tolyl)-20-(4-hydroxyphenyl) porphy--rin covalently attached to Merrifield's peptide resin was prepared. The catalysts exhibit high reactivity and p-selectivity selectivity toward the epoxidation of Δ5-steroids derivatives with PhIO. Under mild reaction conditions, the catalyst was consecutively reused four times without detectable catalyst leaching and gave, over 90% epoxide yield, over 99% P-selectivity respectively.we are interested in using ruthenium porphyrin to a solid support through a covalent linkage forming stable catalysts. The polymer-supported ruthenium (VI) porphyrins were found more efficient for Δ5-steroids derivatives epoxidation (95% yield) than those obtained with corresponding soluble Ru-porphyrins. In the reused experiments, the supported catalysts are clearly superior to corresponding soluble Ru -porphyrins in better yields.