Epoxidation using Oxone

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. 

Several efficient procedures for alkene epoxidation using Oxone were reported, such as Oxone/aqueous NaOH, Oxone/acetone, Oxone/water , Oxone/PTC/benzene/ aqueous buffer solution or Oxone/2-butanone system. Thus, sorbic acid can be regioselectively oxidized using Oxone/aqueous NaOH to 4,5-epoxy-2-hexenoic acid in 84% yield. Similarly, cyclooctene is oxidized to cyclooctene oxide in 81% yield, just by stirring it with Oxone in water . 1-Dodecene is epoxidized in good yield by Oxone/PTC in benzene aqueous buffer solution. It is otherwise difficult to epoxidize 1-dodecene by other oxidizing reagents. ... 

Recently, Hashimoto and Kanda reported a simple and efficient epoxidation using Oxone in a biphasic system of ethyl acetate and water. This reaction is suitable for large-scale preparation of epoxides and does not require any PTC or pH control (equation 45). 

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 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. 

Previously, some fluorocyclohexanones were used in a catalytic amount with Oxone for asymmetric epoxidation reaction, but they gave a poor ee . It was found later that chiral ketones derived from fructose work well as asymmetric epoxidation catalysts and show high enantioselectivity in reactions of /rani-disubstituted and trisubsti-tuted olefins ". Cis and terminal olefins show low ee under these reaction conditions. Interestingly, the catalytic efficiency was enhanced dramatically upon raising the pH. Another asymmetric epoxidation was also reported using Oxone with keto bile acids. ... 

We recently reported our results on the asymmetric epoxidation of trans-disubstituted and trisubstituted alkenes, using Oxone as oxidant, catalyzed by readily available arabinose-derived 4-uloses containing tunable steric blockers that control the enantioselectivity of the epoxidation.Ulose (3), containing a 2, 3 -diisobutyl acetal unit, was the most efficient catalyst and displayed good enantioselectivity. 

The enantioselective epoxidation using [diphenylazepinium] [TRISPHAT] salts as catalysts is an easily reproducible procedure that requires no particular precautions except in the handling of Oxone . Although moderate levels of enantiomeric excess are observed, this reaction can be applied to a wide range of olefins, and both enantiomers of the catalyst are readily available through the use of the S) or (R) enantiomers of 3,3-dimethylbutan-2-amine. The results of a small screen using [6-A-((5)-3,3-dimethylbutan-2-yl)-5/7-dibenz[c,e]azepinium][rac-TRISPHAT] salt as catalyst are reported in Table 6.1... 

Denmark has developed a practical dioxirane-mediated protocol for the catalytic epoxidation of alkenes, which uses Oxone as a terminal oxidant. The olefins studied were epoxidized in 83-96% yield. Of the many reaction parameters examined in this biphasic system, the most influential were found to be the reaction pH, the lipophilicity of the phase-transfer catalyst, and the counterion present. In general, optimal conditions feature 10 mol% of the catalyst l-dodecyl-l-methyl-4-oxopiperidinium triflate (30) and a pH 7.5-8.0 aqueous-methylene chloride biphasic solvent system [95JOC1391]. 

In the Shi epoxidation, an oxone (potassium persulfate, KOSO2OOH) in the presence of a fructose-derived catalyst, 7.57, generates epoxides with high enantiomeric excess oxone is best used to oxidize aldehydes to carboxylic acids in the presence of DMF. 

Denmark and Wu used 0-labeled ketone 81 in their studies of epoxidation of 1-phenylcyclohexene, yielding the conclusion that dioxiranes are the reactive oxidants in monophasic epoxidations with Oxone <1997JOC8964>. 

The procedure described here provides a simple and convenient method for the preparation of a variety of epoxides. It uses Oxone , an inexpensive, safe, and easily handled reagent as the terminal oxidant. The epoxidation reactions are environmentally acceptable processes as Oxone only produces non-toxic potassium hydrogen sulfate and oxygen as the by-products. 

A range of structurally different chiral primary amines was converted into the corresponding iminium tetraphenylborate salts (Fig. 5.3) and tested in the asymmetric epoxidation of a standard test substrate, 1-phenylcyclohexene, using Oxone (4 equiv) as the stoichiometric oxidant, sodium carbonate (8 equiv) as base, in acetonitrile/water (2 1) at 0 °C (Table 5.1) [19,21]. 

For epoxidation to proceed, the presence of base is essential under the aqueous conditions when using Oxone as oxidant. We were pleased to discover that, in contrast, the addition of 1 equiv of any of a range of bases (KF, TBAF, CsF, pyridine, 2,6-lutidine, DBN, DBU, DABCO, LiH, NaH) to the test reaction in dichloromethane at 0 °C, with TPPP as oxidant, did not improve the reaction indeed, the amine bases suppressed epoxidation altogether. 

Recently, exceptional progress has been made in the development of chiral ketones (via dioxirane intermediates) based on asymmetric epoxidations (Eq. 3.10). Although the first such type of asymmetric epoxidation was carried out by Curci in 1984, it is only in the last decade that excellent enantioselectivity of such epoxidations has been achieved. Two of the most prevalent workers in the area are Shi " (by using chiral sugar-based ketone, 3.4) and Yang (chiral binapthalene derivative, 3.5). Often, these reactions are performed by using Oxone in an aqueous environment. Many other chiral ketones have also been developed and these methods have been used in various syntheses. This subject has been reviewed by many authors. ... 

Carbohydrates as Chiral Catalysts. - A review on asymmetric epoxidation using chiral ketones as catalysts includes a section discussing the work of, in particular, Shi on the generation in situ of dioxiranes from sugar ketones and oxone, and their use in the asymmetric epoxidation of traws-alkenes. ... 

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