Oxone epoxidation

Epoxidation Oxone alone (1.5-2 equiv.) can effect epoxidation of alkenes. Yields are generally higher if the pH is maintained at 6 by addition of KOH. Water-soluble substrates (sorbic acid) are epoxidized in water aqueous methanol is used for water-insoluble substrates. 

Epoxidation. Oxone decomposes in the presence of a ketone (such as acetone) to form a species, possibly a dioxirane (a), which can epoxidize alkenes in high yield in reactions generally conducted in CH2C12-H20 with a phase-transfer catalyst. An added ketone is not necessary for efficient epoxidation of an unsaturated ketone. The method is particularly useful for preparation of epoxides that are unstable to heat or acids and bases.3 The acetone-Oxone system is comparable to m-chloroperbenzoic acid in the stereoselectivity of epoxidation of allylic alcohols. It is also similar to the peracid in preferential attack of the double bond in geraniol (dienol) that is further removed from the hydroxyl group.4... 

Epoxidation. Oxone is used to generate dioxirane from a ketone added to the reaction medium. Such dioxiranes epoxidize alkenes stereoselectively. 2-Cyclo-hexenol gives two epoxy alcohols in a ratio of 77 23 (trans cis). 

Epoxidation. Oxone is used to t (9 examples, 83-96%). A-Meth> l-.V-d catalyst. 

Oxone, K2C03 Shi s asymmetric epoxidation with ketone 1. 

Many other reagents for converting alkenes to epoxides,including H2O2 and Oxone , VO(0-isopropyl)3 in liquid C02, ° polymer-supported cobalt (II) acetate and 02, ° and dimethyl dioxirane.This reagent is rather versatile, and converts methylene oxiranes to spiro-epoxides. ° ° One problem with dimethyloxirane is C—H insertion reactions rather than epoxidation. Magnesium monoperoxyphthalate is commercially available, and has been shown to be a good substitute for m-chloroperoxybenzoic acid in a number of reactions. 

The pollutant (xenobiotic) forms a stable covalent bond with its target. Examples include the phosphorylation of cholinesterases by the oxon forms of OPs, the formation of DNA adducts by the reactive epoxides of benzo[a] pyrene and other PAHs, and the binding of organomercury compounds to... 

To mimic the square-pyramidal coordination of iron bleomycin, a series of iron (Il)complexes with pyridine-containing macrocycles 4 was synthesized and used for the epoxidation of alkenes with H2O2 (Scheme 4) [35]. These macrocycles bear an aminopropyl pendant arm and in presence of poorly coordinating acids like triflic acid a reversible dissociation of the arm is possible and the catalytic active species is formed. These complexes perform well in alkene epoxidations (66-89% yield with 90-98% selectivity in 5 min at room temperature). Furthermore, recyclable terpyridines 5 lead to highly active Fe -complexes, which show good to excellent results (up to 96% yield) for the epoxidation with oxone at room temperature (Scheme 4) [36]. 

Epoxidation of cyclooctene and other alkenes with Oxone (KHSO5) was promoted effectively in an aqueous micellar solution of an amphiphilic ketone (3.3).52 The amphiphilic ketone can be easily derived from hepta(ethylene glycol) monodecyl ether. 

The simplest model compound is cyclohexene oxide III. Monomers IV, V and VII represent different aspects of the ester portion of I, while monomers VII and VIII reflect aspects of both the monomer I and the polymer which is formed by cationic ring-opening polymerization. Monomers IV-VII were prepared using a phase transfer catalyzed epoxidation based on the method of Venturello and D Aloisio (6) and employed previously in this laboratory (7). This method was not effective for the preparation of monomer VIII. In this specific case (equation 4), epoxidation using Oxone (potassium monoperoxysulfate) was employed. 

As oxiranes can be generated in situ from Oxone (potassium peroxomono-sulfate) and a ketone, dioxiranes are attractive oxidants for epoxidation reactions that may be rapid and may require only a simple workup. 

All the reactions were carried out at 0°C, with the substrate (1 equivalent), ketone (3 equivalents), Oxone (5 equivalents), and NaHCC>3 in CH3CN aqueous EDTA for 2 hours. High enantioselectivity can generally be obtained for trans- and trisubstituted olefins. The favored spiro and planar transition states have been proposed for ketone 130-mediated rrans-stilbene epoxidation (Scheme 4-48). 

Cao et al.102 extended their discovery to the asymmetric epoxidation of enynes using ketone 130 as the catalyst and Oxone as the oxidant (Scheme 4-50). 

Subsequently, high chemoselectivity and enantioselectivity have been observed in the asymmetric epoxidation of a variety of conjugated enynes using fructose-derived chiral ketone as the catalyst and Oxone as the oxidant. Reported enantioselectivities range from 89% to 97%, and epoxidation occurs chemoselectively at the olefins. In contrast to certain isolated trisubstituted olefins, high enantioselectivity for trisubstituted enynes is noticeable. This may indicate that the alkyne group is beneficial for these substrates due to both electronic and steric effects. 

The epoxidation of nonfunctionalized alkenes may also be effected by chiral dioxiranes. These species, formed in situ using the appropriate ketone and potassium caroate (Oxone), can be formed from C-2 symmetric chiral ketones (29)[93], functionalized carbohydrates (30)[94] or alkaloid derivatives (31)[95]. One example from the laboratories of Shi and co-workers is given in Scheme 19. 

Among many other methods for epoxidation of disubstituted E-alkenes, chiral dioxiranes generated in situ from potassium peroxomonosulfate and chiral ketones have appeared to be one of the most efficient. Recently, Wang et /. 2J reported a highly enantioselective epoxidation for disubstituted E-alkenes and trisubstituted alkenes using a d- or L-fructose derived ketone as catalyst and oxone as oxidant (Figure 6.3). 

Epoxidation using a chiral fructose-derived ketone is easy to carry out, as it occurs in aqueous conditions. The reactions were performed without any modification of the published procedure. The glassware has to be free of trace metal, which can decompose the oxone the use of a plastic spatula is recommended and the volumes must be measured using glass-graduated cylinders. Table 6.2 gives different examples of epoxides which can be obtained using the method prescribed. 

Epoxyketone 60 has also been prepared by hydroxyselenation of 4-acetyl-1-methylcyclohexene with phenylselenium chloride and water, oxidation of the selenide to selenoxide with buffered aqueous oxone, and elimination of the se-lenoxide in the same pot to provide the epoxide [80]. Control of the conditions was essential to prevent epimerization of the ketone. This route has little to recommend it given the expense and toxicity of the reagents, the moderate yield, and the problems with epimerization. 

Wang and Shi have published a detailed study of their fructose-based dioxirane epoxidation catalyst system with hydroxyalkene substrates. The ees obtained were highly pH dependent. The lower enantioselectivity obtained at low pH is attributed to the substantial contribution of direct epoxidation by Oxone. The results obtained with... 

Asymmetric epoxidation of olefins is an effective approach for the synthesis of enan-tiomerically enriched epoxides. A variety of efficient methods have been developed [1, 2], including Sharpless epoxidation of allylic alcohols [3, 4], metal-catalyzed epoxidation of unfunctionalized olefins [5-10], and nucleophilic epoxidation of electron-deficient olefins [11-14], Dioxiranes and oxazirdinium salts have been proven to be effective oxidation reagents [15-21], Chiral dioxiranes [22-28] and oxaziridinium salts [19] generated in situ with Oxone from ketones and iminium salts, respectively, have been extensively investigated in numerous laboratories and have been shown to be useful toward the asymmetric epoxidation of alkenes. In these epoxidation reactions, only a catalytic amount of ketone or iminium salt is required since they are regenerated upon epoxidation of alkenes (Scheme 1). 

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