Monoperoxyphthalic epoxidation

Three peroxyacids are produced commercially for the merchant market peroxyacetic acid as a 40 wt % solution in acetic acid, y -chloroperoxybenzoic acid, and magnesium monoperoxyphthalate hexahydrate. Other peroxyacids are produced for captive use, eg, peroxyformic acid generated in situ as an epoxidizing agent. 

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. 

Another one-step addition reaction to C=C double bonds that forms three-membered rings is the epoxidation of alkenes with percarboxylic acids (Figure 3.19). Most often, meta-chloroperbenzoic acid (MCPBA) is used for epoxidations. Magnesium monoperoxyphthalate (MMPP) has become an alternative. Imidopercarboxylic acids are used to epoxidize olefins as well. Their use (for this purpose) is mandatory when the substrate contains a ketonic C=0 double bond in addition to the C=C double bond. In compounds of this type, percarboxylic acids preferentially cause a Baeyer-Villiger oxidation of the ketone (see Section 14.4.2), whereas imidopercarboxylic acids selectively effect epoxidations (for an example see Figure 14.35). 

A third one-step addition reaction to C=C double bonds that forms three-membered rings is the epoxidation of olefins with percarboxylic acids (Figure 3.14). Suitable percarboxylic acids must, however, not be (too) explosive. Thus, aromatic percarboxylic adds are preferable. Until recently one epoxidized almost exclusively with mefa-chloroper-benzoic acid (MCPBA). An alternative has become magnesium monoperoxyphthalate (MMPP). In the transition state of this type of epoxidation, four electron pairs are shifted simultaneously (which is a record in this book except for the Corey-Winter elimination in Figure 4.42). 

Magnesium monoperoxyphthalate (MMPP) epoxidizes alkenes much like MCPBA. MMPP is more stable, however, and it may be safer to use for large-scale and industrial reactions. Propose a mechanism for the reaction of fraw,s-2-methylhept-3-ene with MMPP, and predict the structure of the product(s). 

An abbreviation for mefa-chloroperoxybenzoic acid, a common epoxidizing agent, (p. 646) An abbreviation for magnesium monoperoxyphthalate, a relatively stable peroxyacid often used in large-scale epoxidations. (p. 646)... 

Ye, D Fringuelli, F. Piermatti, O. Pizzo, F., Highly Diastereoselective Epoxidation of Cycloalkenols with Monoperoxyphthalic Acid in Water. / Org. Chem. 1997, 62, 3748. 

Diethyl 4,5- and 5,6-epoxyalkyIphosphonates are prepared by treatment of the corresponding 4,5-and 5,6-unsaturated phosphonates with MCPBA in CH2CI2 at 4O C - or aqueous solution of monoperoxyphthalate in z-PrOH at room temperature.The epoxidation of the double bond of a 6-oxo-7,8-unsaturated phosphonate involves the use of H2O2 in NaOH-MeOH solution to provide the corresponding 7,8-epoxyphosphonate in 90% yield. 

Magnesium monoperoxyphthalate has also been used in the epoxidation of vinylarenes, as shown in Eq. (14) [27],... 

We began our work with isoprene alcohol (see Scheme 11). While the Prilezhaev reaction with monoperoxyphthalic acid provided the appropriate dimethyl glycidol in good yield, we failed in our attempts to prepare the corresponding chiral epoxide by Sharpless epoxidation. Obviously, the reaction does not work in the case of this tertiary allylic alcohol. When the solution is allowed to warm up to room temperature a slow epoxidation takes place, however, the isolated dimethyl glycidol does not show any optical activity. Very recently the asymmetric epoxidation of a tertiary allylic alcohol in reasonable optical and chemical yield has been described [21]. 

The magnesium salt of monoperoxyphthalic acid is an alternative. Peroxyacetic acid, peroxybenzoic acid, and peroxytrifluoroacetic acid also are used frequently for epoxidation. All of the peroxycarboxylic acids are potentially explosive materials and require careful handling. Potassium hydrogen peroxysulfate, which is sold commercially as Oxone , is a convenient reagent for epoxidations that can be done in aqueous solution. 

Inert solvents are required when using peroxybenzoic or monoperoxyphthalic acid epoxidation by peroxyacetic acid can be carried out in acetic acid as solvent if strong mineral acids (which are often used as catalyst for formation of the peroxy acid) are absent and the reaction temperature is below 30°. 

Monoperoxyphthalic acid can be used for preparation of epoxides in the same way as peroxybenzoic acid. In general, good yields are obtained under almost the same conditions as with peroxybenzoic acid, but monoperoxyphthalic acid has the advantage that it is more stable. Because of this stability monoperoxyphthalic acid is particularly suited for epoxidation of less reactive olefins when reaction is effected in chloroform solution the phthalic acid produced is readily separated because it is insoluble in this solvent. 

Epoxidation by monoperoxyphthalic acid has achieved particular importance in the chemistry of natural products.28,39... 

In contrast epoxidation of geraniol with monoperoxyphthalic acid in the presence of cetyltrimethylammonium hydroxide (surfactant) effects almost exclusive epoxidation of the allylic double bond to give 2,3-epoxygeraniol in 90% yield. Epoxidation with MPPA in NaHCOs solution shows the opposite regioseleclivity and provides 6,7-epoxygeraniol in 72% yield. 

For the synthesis of (4jR,4 / )-isozeaxanthin (4R,4 R-129), optically active (-)-(5)-a-ionone (79) was stereoselectively epoxidized to the cw-epoxide 80 with monoperoxyphthalic acid. 

The peroxyacid epoxidation is quite general, with electron-rich double bonds reacting fastest. The following reactions are difficult transformations made possible by this selective, stereospecific epoxidation procedure. The second example uses magnesium monoperoxyphthalate (MMPP), a relatively stable water-soluble peroxyacid often used in large-scale epoxidations. 

The reaction occurs between the aqueous solution of MCPBA and the emulsified substrate (Ch. 9, p. 348). A comparison was made with the similar reaction using magnesium monoperoxyphthalate (MMPP), in aqueous ethanol suspensions. In general, MCPBA reacts faster and is more selective and higher yielding than MMPP. Most of the reactions go to completion within a few minutes, while the silent process requires several hours. Excellent selectivities are observed, and terminal olefins can be kept intact in the presence of central ones. Under the experimental conditions, methyl zso-ricinoleate imdergoes epoxidation followed by cyclization to the tetrahydrofuranic compoimd. 

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