Peroxyacids epoxidation with

Peroxyacid (Section 7.8) A compound with the -C03H functional group. Peroxyacids react with alkenes to give epoxides. 

Alkenes can be epoxidized with any of a number of peroxyacids, " of which m-chloroperoxybenzoic has been the most often used. The reaction, called the... 

Hydroxy-terminated polybutadiene (8) (HTPB) has been treated with dinitrogen pentoxide in methylene chloride. The product (9) is an energetic oligomer but is unlikely to find application because of the inherent instability of /3-nitronitrates." Initial peroxyacid epoxidation of some of the double bonds of HTPB followed by reaction with dinitrogen pentoxide yields a product containing vtc-dinitrate ester groups and this product (NHTPB) is of much more interest as an energetic binder (see Section 3.10)." ... 

A peroxyacid epoxidizes an alkene by a concerted electrophilic reaction where several bonds are broken and several are formed at the same time. Starting with the alkene and the peroxyacid, a one-step reaction gives the epoxide and the acid directly, without any intermediates. 

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 monoper-oxyphthalate (MMPP), a relatively stable water-soluble peroxyacid often used in large-scale epoxidations. These aqueous MMPP epoxidations, carried out at neutral pH to avoid opening the epoxide, avoid the large-scale use of hazardous chlorinated solvents. 

During the first total synthesis of briarellin diterpenes, briarellins E and F, L.E. Overman and co-workers utilized the large reactivity difference between a triple and a double bond in peroxyacid oxidations to selectively epoxidize a trisubstituted double bond in the presence of a terminal alkyne." The epoxidation with mCPBA was carried out in DCM in the presence of a base to afford the a-epoxide in a 9 1 diastereomeric ratio. 

An interesting difference in stereoselectivity between epoxidations using peroxyacid and peroxide is revealed in the reaction of (9) with 3-ClCgH CO H (MCPBA) and Me COOH (TBHP)2. Only the B-epoxide was formed using the former whereas a mixture of both stereoisomers resulted frcm epoxidation with TBHP. 

Oxidation of an alkene with a peroxyacid leads to an epoxide, with a carboxylic acid as the by-product. 

Oxidation of an alkene with a peroxyacid leads to an epoxide, with a carboxylic acid as the by-produet 18,37,38,40,42,44, 51. Oxidative cleavage of an alkene with ozone leads to an ozonide. Reductive workup with dimethyl sulfoxide or zinc and acetic acid gives ketones and/or aldehydes. Oxidative workup with hydrogen peroxide gives ketones and/or earboxylic acids 19,20, 21, 22,36,39,41,44. 

Unsaturated polymers, prepared from butadiene or isoprene, can be epoxidized with peroxyacids. The peroxyacids used can either be preformed or prepared in situ by reacting hydrogen peroxide with lower aliphatic carboxylic acids. The epoxidized polymers can be reacted with diamines or dianhydrides to give a cross-linked resin useful for adhesive and coating applications. 

Alkenes are oxidized to give epoxides on treatment with a peroxyacid (RCO H), such as mefn-chloroperoxybenzoic acid. An epoxide, also called an oxirane, is a cyclic ether with an oxygen atom in a three-membered ring. For example ... 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

In the laboratory, as we saw in Section 7.8, epoxides are prepared by treatment of an alkene with a peroxyacid (RC03H), typically m-chloroperoxybenzoic acid. 

Treatment of the following alkene with a peroxyacid yields an epoxide different from that obtained by reaction with aqueous Br2 followed by base treatment. Propose structures for the two epoxides, and explain the result. 

The rate of epoxidation of alkenes is increased by alkyl groups and other ERG substituents and the reactivity of the peroxy acids is increased by EWG substituents.72 These structure-reactivity relationships demonstrate that the peroxyacid acts as an electrophile in the reaction. Decreased reactivity is exhibited by double bonds that are conjugated with strongly electron-attracting substituents, and more reactive peroxyacids, such as trifluoroperoxyacetic acid, are required for oxidation of such compounds.73 Electron-poor alkenes can also be epoxidized by alkaline solutions of... 

Alkenes are also oxidized to epoxides hy peracid or peroxyacid (RCO3H), e.g. peroxyhenzoic acid (C6H5CO3H). A peroxyacid contains an extra oxygen atom compared with carboxylic acid, and this extra oxygen is added to the double bond of an alkene to give an epoxide. For example, cyclohexene reacts with peroxyhenzoic acid to produce cyclohexane oxide. 

---